block: first step of splitting ll_rw_blk, rename it

Then we retain history in blk-core.c

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 4457 insertions, 0 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
new file mode 100644
index 000000000000..1932a56f5e4b
--- /dev/null
+++ b/block/blk-core.c
@@ -0,0 +1,4457 @@
+/*
+ * Copyright (C) 1991, 1992 Linus Torvalds
+ * Copyright (C) 1994,      Karl Keyte: Added support for disk statistics
+ * Elevator latency, (C) 2000  Andrea Arcangeli <andrea@suse.de> SuSE
+ * Queue request tables / lock, selectable elevator, Jens Axboe <axboe@suse.de>
+ * kernel-doc documentation started by NeilBrown <neilb@cse.unsw.edu.au> -  July2000
+ * bio rewrite, highmem i/o, etc, Jens Axboe <axboe@suse.de> - may 2001
+ */
+
+/*
+ * This handles all read/write requests to block devices
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/backing-dev.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/highmem.h>
+#include <linux/mm.h>
+#include <linux/kernel_stat.h>
+#include <linux/string.h>
+#include <linux/init.h>
+#include <linux/bootmem.h>      /* for max_pfn/max_low_pfn */
+#include <linux/completion.h>
+#include <linux/slab.h>
+#include <linux/swap.h>
+#include <linux/writeback.h>
+#include <linux/task_io_accounting_ops.h>
+#include <linux/interrupt.h>
+#include <linux/cpu.h>
+#include <linux/blktrace_api.h>
+#include <linux/fault-inject.h>
+#include <linux/scatterlist.h>
+
+/*
+ * for max sense size
+ */
+#include <scsi/scsi_cmnd.h>
+
+static void blk_unplug_work(struct work_struct *work);
+static void blk_unplug_timeout(unsigned long data);
+static void drive_stat_acct(struct request *rq, int new_io);
+static void init_request_from_bio(struct request *req, struct bio *bio);
+static int __make_request(struct request_queue *q, struct bio *bio);
+static struct io_context *current_io_context(gfp_t gfp_flags, int node);
+static void blk_recalc_rq_segments(struct request *rq);
+static void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
+                            struct bio *bio);
+
+/*
+ * For the allocated request tables
+ */
+static struct kmem_cache *request_cachep;
+
+/*
+ * For queue allocation
+ */
+static struct kmem_cache *requestq_cachep;
+
+/*
+ * For io context allocations
+ */
+static struct kmem_cache *iocontext_cachep;
+
+/*
+ * Controlling structure to kblockd
+ */
+static struct workqueue_struct *kblockd_workqueue;
+
+unsigned long blk_max_low_pfn, blk_max_pfn;
+
+EXPORT_SYMBOL(blk_max_low_pfn);
+EXPORT_SYMBOL(blk_max_pfn);
+
+static DEFINE_PER_CPU(struct list_head, blk_cpu_done);
+
+/* Amount of time in which a process may batch requests */
+#define BLK_BATCH_TIME  (HZ/50UL)
+
+/* Number of requests a "batching" process may submit */
+#define BLK_BATCH_REQ   32
+
+/*
+ * Return the threshold (number of used requests) at which the queue is
+ * considered to be congested.  It include a little hysteresis to keep the
+ * context switch rate down.
+ */
+static inline int queue_congestion_on_threshold(struct request_queue *q)
+{
+        return q->nr_congestion_on;
+}
+
+/*
+ * The threshold at which a queue is considered to be uncongested
+ */
+static inline int queue_congestion_off_threshold(struct request_queue *q)
+{
+        return q->nr_congestion_off;
+}
+
+static void blk_queue_congestion_threshold(struct request_queue *q)
+{
+        int nr;
+
+        nr = q->nr_requests - (q->nr_requests / 8) + 1;
+        if (nr > q->nr_requests)
+                nr = q->nr_requests;
+        q->nr_congestion_on = nr;
+
+        nr = q->nr_requests - (q->nr_requests / 8) - (q->nr_requests / 16) - 1;
+        if (nr < 1)
+                nr = 1;
+        q->nr_congestion_off = nr;
+}
+
+/**
+ * blk_get_backing_dev_info - get the address of a queue's backing_dev_info
+ * @bdev:       device
+ *
+ * Locates the passed device's request queue and returns the address of its
+ * backing_dev_info
+ *
+ * Will return NULL if the request queue cannot be located.
+ */
+struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev)
+{
+        struct backing_dev_info *ret = NULL;
+        struct request_queue *q = bdev_get_queue(bdev);
+
+        if (q)
+                ret = &q->backing_dev_info;
+        return ret;
+}
+EXPORT_SYMBOL(blk_get_backing_dev_info);
+
+/**
+ * blk_queue_prep_rq - set a prepare_request function for queue
+ * @q:          queue
+ * @pfn:        prepare_request function
+ *
+ * It's possible for a queue to register a prepare_request callback which
+ * is invoked before the request is handed to the request_fn. The goal of
+ * the function is to prepare a request for I/O, it can be used to build a
+ * cdb from the request data for instance.
+ *
+ */
+void blk_queue_prep_rq(struct request_queue *q, prep_rq_fn *pfn)
+{
+        q->prep_rq_fn = pfn;
+}
+
+EXPORT_SYMBOL(blk_queue_prep_rq);
+
+/**
+ * blk_queue_merge_bvec - set a merge_bvec function for queue
+ * @q:          queue
+ * @mbfn:       merge_bvec_fn
+ *
+ * Usually queues have static limitations on the max sectors or segments that
+ * we can put in a request. Stacking drivers may have some settings that
+ * are dynamic, and thus we have to query the queue whether it is ok to
+ * add a new bio_vec to a bio at a given offset or not. If the block device
+ * has such limitations, it needs to register a merge_bvec_fn to control
+ * the size of bio's sent to it. Note that a block device *must* allow a
+ * single page to be added to an empty bio. The block device driver may want
+ * to use the bio_split() function to deal with these bio's. By default
+ * no merge_bvec_fn is defined for a queue, and only the fixed limits are
+ * honored.
+ */
+void blk_queue_merge_bvec(struct request_queue *q, merge_bvec_fn *mbfn)
+{
+        q->merge_bvec_fn = mbfn;
+}
+
+EXPORT_SYMBOL(blk_queue_merge_bvec);
+
+void blk_queue_softirq_done(struct request_queue *q, softirq_done_fn *fn)
+{
+        q->softirq_done_fn = fn;
+}
+
+EXPORT_SYMBOL(blk_queue_softirq_done);
+
+/**
+ * blk_queue_make_request - define an alternate make_request function for a device
+ * @q:  the request queue for the device to be affected
+ * @mfn: the alternate make_request function
+ *
+ * Description:
+ *    The normal way for &struct bios to be passed to a device
+ *    driver is for them to be collected into requests on a request
+ *    queue, and then to allow the device driver to select requests
+ *    off that queue when it is ready.  This works well for many block
+ *    devices. However some block devices (typically virtual devices
+ *    such as md or lvm) do not benefit from the processing on the
+ *    request queue, and are served best by having the requests passed
+ *    directly to them.  This can be achieved by providing a function
+ *    to blk_queue_make_request().
+ *
+ * Caveat:
+ *    The driver that does this *must* be able to deal appropriately
+ *    with buffers in "highmemory". This can be accomplished by either calling
+ *    __bio_kmap_atomic() to get a temporary kernel mapping, or by calling
+ *    blk_queue_bounce() to create a buffer in normal memory.
+ **/
+void blk_queue_make_request(struct request_queue * q, make_request_fn * mfn)
+{
+        /*
+         * set defaults
+         */
+        q->nr_requests = BLKDEV_MAX_RQ;
+        blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
+        blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
+        q->make_request_fn = mfn;
+        q->backing_dev_info.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+        q->backing_dev_info.state = 0;
+        q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
+        blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
+        blk_queue_hardsect_size(q, 512);
+        blk_queue_dma_alignment(q, 511);
+        blk_queue_congestion_threshold(q);
+        q->nr_batching = BLK_BATCH_REQ;
+
+        q->unplug_thresh = 4;           /* hmm */
+        q->unplug_delay = (3 * HZ) / 1000;      /* 3 milliseconds */
+        if (q->unplug_delay == 0)
+                q->unplug_delay = 1;
+
+        INIT_WORK(&q->unplug_work, blk_unplug_work);
+
+        q->unplug_timer.function = blk_unplug_timeout;
+        q->unplug_timer.data = (unsigned long)q;
+
+        /*
+         * by default assume old behaviour and bounce for any highmem page
+         */
+        blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
+}
+
+EXPORT_SYMBOL(blk_queue_make_request);
+
+static void rq_init(struct request_queue *q, struct request *rq)
+{
+        INIT_LIST_HEAD(&rq->queuelist);
+        INIT_LIST_HEAD(&rq->donelist);
+
+        rq->errors = 0;
+        rq->bio = rq->biotail = NULL;
+        INIT_HLIST_NODE(&rq->hash);
+        RB_CLEAR_NODE(&rq->rb_node);
+        rq->ioprio = 0;
+        rq->buffer = NULL;
+        rq->ref_count = 1;
+        rq->q = q;
+        rq->special = NULL;
+        rq->data_len = 0;
+        rq->data = NULL;
+        rq->nr_phys_segments = 0;
+        rq->sense = NULL;
+        rq->end_io = NULL;
+        rq->end_io_data = NULL;
+        rq->completion_data = NULL;
+        rq->next_rq = NULL;
+}
+
+/**
+ * blk_queue_ordered - does this queue support ordered writes
+ * @q:        the request queue
+ * @ordered:  one of QUEUE_ORDERED_*
+ * @prepare_flush_fn: rq setup helper for cache flush ordered writes
+ *
+ * Description:
+ *   For journalled file systems, doing ordered writes on a commit
+ *   block instead of explicitly doing wait_on_buffer (which is bad
+ *   for performance) can be a big win. Block drivers supporting this
+ *   feature should call this function and indicate so.
+ *
+ **/
+int blk_queue_ordered(struct request_queue *q, unsigned ordered,
+                      prepare_flush_fn *prepare_flush_fn)
+{
+        if (ordered & (QUEUE_ORDERED_PREFLUSH | QUEUE_ORDERED_POSTFLUSH) &&
+            prepare_flush_fn == NULL) {
+                printk(KERN_ERR "blk_queue_ordered: prepare_flush_fn required\n");
+                return -EINVAL;
+        }
+
+        if (ordered != QUEUE_ORDERED_NONE &&
+            ordered != QUEUE_ORDERED_DRAIN &&
+            ordered != QUEUE_ORDERED_DRAIN_FLUSH &&
+            ordered != QUEUE_ORDERED_DRAIN_FUA &&
+            ordered != QUEUE_ORDERED_TAG &&
+            ordered != QUEUE_ORDERED_TAG_FLUSH &&
+            ordered != QUEUE_ORDERED_TAG_FUA) {
+                printk(KERN_ERR "blk_queue_ordered: bad value %d\n", ordered);
+                return -EINVAL;
+        }
+
+        q->ordered = ordered;
+        q->next_ordered = ordered;
+        q->prepare_flush_fn = prepare_flush_fn;
+
+        return 0;
+}
+
+EXPORT_SYMBOL(blk_queue_ordered);
+
+/*
+ * Cache flushing for ordered writes handling
+ */
+inline unsigned blk_ordered_cur_seq(struct request_queue *q)
+{
+        if (!q->ordseq)
+                return 0;
+        return 1 << ffz(q->ordseq);
+}
+
+unsigned blk_ordered_req_seq(struct request *rq)
+{
+        struct request_queue *q = rq->q;
+
+        BUG_ON(q->ordseq == 0);
+
+        if (rq == &q->pre_flush_rq)
+                return QUEUE_ORDSEQ_PREFLUSH;
+        if (rq == &q->bar_rq)
+                return QUEUE_ORDSEQ_BAR;
+        if (rq == &q->post_flush_rq)
+                return QUEUE_ORDSEQ_POSTFLUSH;
+
+        /*
+         * !fs requests don't need to follow barrier ordering.  Always
+         * put them at the front.  This fixes the following deadlock.
+         *
+         * http://thread.gmane.org/gmane.linux.kernel/537473
+         */
+        if (!blk_fs_request(rq))
+                return QUEUE_ORDSEQ_DRAIN;
+
+        if ((rq->cmd_flags & REQ_ORDERED_COLOR) ==
+            (q->orig_bar_rq->cmd_flags & REQ_ORDERED_COLOR))
+                return QUEUE_ORDSEQ_DRAIN;
+        else
+                return QUEUE_ORDSEQ_DONE;
+}
+
+void blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
+{
+        struct request *rq;
+
+        if (error && !q->orderr)
+                q->orderr = error;
+
+        BUG_ON(q->ordseq & seq);
+        q->ordseq |= seq;
+
+        if (blk_ordered_cur_seq(q) != QUEUE_ORDSEQ_DONE)
+                return;
+
+        /*
+         * Okay, sequence complete.
+         */
+        q->ordseq = 0;
+        rq = q->orig_bar_rq;
+
+        if (__blk_end_request(rq, q->orderr, blk_rq_bytes(rq)))
+                BUG();
+}
+
+static void pre_flush_end_io(struct request *rq, int error)
+{
+        elv_completed_request(rq->q, rq);
+        blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
+}
+
+static void bar_end_io(struct request *rq, int error)
+{
+        elv_completed_request(rq->q, rq);
+        blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_BAR, error);
+}
+
+static void post_flush_end_io(struct request *rq, int error)
+{
+        elv_completed_request(rq->q, rq);
+        blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_POSTFLUSH, error);
+}
+
+static void queue_flush(struct request_queue *q, unsigned which)
+{
+        struct request *rq;
+        rq_end_io_fn *end_io;
+
+        if (which == QUEUE_ORDERED_PREFLUSH) {
+                rq = &q->pre_flush_rq;
+                end_io = pre_flush_end_io;
+        } else {
+                rq = &q->post_flush_rq;
+                end_io = post_flush_end_io;
+        }
+
+        rq->cmd_flags = REQ_HARDBARRIER;
+        rq_init(q, rq);
+        rq->elevator_private = NULL;
+        rq->elevator_private2 = NULL;
+        rq->rq_disk = q->bar_rq.rq_disk;
+        rq->end_io = end_io;
+        q->prepare_flush_fn(q, rq);
+
+        elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
+}
+
+static inline struct request *start_ordered(struct request_queue *q,
+                                            struct request *rq)
+{
+        q->orderr = 0;
+        q->ordered = q->next_ordered;
+        q->ordseq |= QUEUE_ORDSEQ_STARTED;
+
+        /*
+         * Prep proxy barrier request.
+         */
+        blkdev_dequeue_request(rq);
+        q->orig_bar_rq = rq;
+        rq = &q->bar_rq;
+        rq->cmd_flags = 0;
+        rq_init(q, rq);
+        if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
+                rq->cmd_flags |= REQ_RW;
+        if (q->ordered & QUEUE_ORDERED_FUA)
+                rq->cmd_flags |= REQ_FUA;
+        rq->elevator_private = NULL;
+        rq->elevator_private2 = NULL;
+        init_request_from_bio(rq, q->orig_bar_rq->bio);
+        rq->end_io = bar_end_io;
+
+        /*
+         * Queue ordered sequence.  As we stack them at the head, we
+         * need to queue in reverse order.  Note that we rely on that
+         * no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
+         * request gets inbetween ordered sequence. If this request is
+         * an empty barrier, we don't need to do a postflush ever since
+         * there will be no data written between the pre and post flush.
+         * Hence a single flush will suffice.
+         */
+        if ((q->ordered & QUEUE_ORDERED_POSTFLUSH) && !blk_empty_barrier(rq))
+                queue_flush(q, QUEUE_ORDERED_POSTFLUSH);
+        else
+                q->ordseq |= QUEUE_ORDSEQ_POSTFLUSH;
+
+        elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
+
+        if (q->ordered & QUEUE_ORDERED_PREFLUSH) {
+                queue_flush(q, QUEUE_ORDERED_PREFLUSH);
+                rq = &q->pre_flush_rq;
+        } else
+                q->ordseq |= QUEUE_ORDSEQ_PREFLUSH;
+
+        if ((q->ordered & QUEUE_ORDERED_TAG) || q->in_flight == 0)
+                q->ordseq |= QUEUE_ORDSEQ_DRAIN;
+        else
+                rq = NULL;
+
+        return rq;
+}
+
+int blk_do_ordered(struct request_queue *q, struct request **rqp)
+{
+        struct request *rq = *rqp;
+        const int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);
+
+        if (!q->ordseq) {
+                if (!is_barrier)
+                        return 1;
+
+                if (q->next_ordered != QUEUE_ORDERED_NONE) {
+                        *rqp = start_ordered(q, rq);
+                        return 1;
+                } else {
+                        /*
+                         * This can happen when the queue switches to
+                         * ORDERED_NONE while this request is on it.
+                         */
+                        blkdev_dequeue_request(rq);
+                        if (__blk_end_request(rq, -EOPNOTSUPP,
+                                              blk_rq_bytes(rq)))
+                                BUG();
+                        *rqp = NULL;
+                        return 0;
+                }
+        }
+
+        /*
+         * Ordered sequence in progress
+         */
+
+        /* Special requests are not subject to ordering rules. */
+        if (!blk_fs_request(rq) &&
+            rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
+                return 1;
+
+        if (q->ordered & QUEUE_ORDERED_TAG) {
+                /* Ordered by tag.  Blocking the next barrier is enough. */
+                if (is_barrier && rq != &q->bar_rq)
+                        *rqp = NULL;
+        } else {
+                /* Ordered by draining.  Wait for turn. */
+                WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
+                if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
+                        *rqp = NULL;
+        }
+
+        return 1;
+}
+
+static void req_bio_endio(struct request *rq, struct bio *bio,
+                          unsigned int nbytes, int error)
+{
+        struct request_queue *q = rq->q;
+
+        if (&q->bar_rq != rq) {
+                if (error)
+                        clear_bit(BIO_UPTODATE, &bio->bi_flags);
+                else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
+                        error = -EIO;
+
+                if (unlikely(nbytes > bio->bi_size)) {
+                        printk("%s: want %u bytes done, only %u left\n",
+                               __FUNCTION__, nbytes, bio->bi_size);
+                        nbytes = bio->bi_size;
+                }
+
+                bio->bi_size -= nbytes;
+                bio->bi_sector += (nbytes >> 9);
+                if (bio->bi_size == 0)
+                        bio_endio(bio, error);
+        } else {
+
+                /*
+                 * Okay, this is the barrier request in progress, just
+                 * record the error;
+                 */
+                if (error && !q->orderr)
+                        q->orderr = error;
+        }
+}
+
+/**
+ * blk_queue_bounce_limit - set bounce buffer limit for queue
+ * @q:  the request queue for the device
+ * @dma_addr:   bus address limit
+ *
+ * Description:
+ *    Different hardware can have different requirements as to what pages
+ *    it can do I/O directly to. A low level driver can call
+ *    blk_queue_bounce_limit to have lower memory pages allocated as bounce
+ *    buffers for doing I/O to pages residing above @page.
+ **/
+void blk_queue_bounce_limit(struct request_queue *q, u64 dma_addr)
+{
+        unsigned long bounce_pfn = dma_addr >> PAGE_SHIFT;
+        int dma = 0;
+
+        q->bounce_gfp = GFP_NOIO;
+#if BITS_PER_LONG == 64
+        /* Assume anything <= 4GB can be handled by IOMMU.
+           Actually some IOMMUs can handle everything, but I don't
+           know of a way to test this here. */
+        if (bounce_pfn < (min_t(u64,0xffffffff,BLK_BOUNCE_HIGH) >> PAGE_SHIFT))
+                dma = 1;
+        q->bounce_pfn = max_low_pfn;
+#else
+        if (bounce_pfn < blk_max_low_pfn)
+                dma = 1;
+        q->bounce_pfn = bounce_pfn;
+#endif
+        if (dma) {
+                init_emergency_isa_pool();
+                q->bounce_gfp = GFP_NOIO | GFP_DMA;
+                q->bounce_pfn = bounce_pfn;
+        }
+}
+
+EXPORT_SYMBOL(blk_queue_bounce_limit);
+
+/**
+ * blk_queue_max_sectors - set max sectors for a request for this queue
+ * @q:  the request queue for the device
+ * @max_sectors:  max sectors in the usual 512b unit
+ *
+ * Description:
+ *    Enables a low level driver to set an upper limit on the size of
+ *    received requests.
+ **/
+void blk_queue_max_sectors(struct request_queue *q, unsigned int max_sectors)
+{
+        if ((max_sectors << 9) < PAGE_CACHE_SIZE) {
+                max_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
+                printk("%s: set to minimum %d\n", __FUNCTION__, max_sectors);
+        }
+
+        if (BLK_DEF_MAX_SECTORS > max_sectors)
+                q->max_hw_sectors = q->max_sectors = max_sectors;
+        else {
+                q->max_sectors = BLK_DEF_MAX_SECTORS;
+                q->max_hw_sectors = max_sectors;
+        }
+}
+
+EXPORT_SYMBOL(blk_queue_max_sectors);
+
+/**
+ * blk_queue_max_phys_segments - set max phys segments for a request for this queue
+ * @q:  the request queue for the device
+ * @max_segments:  max number of segments
+ *
+ * Description:
+ *    Enables a low level driver to set an upper limit on the number of
+ *    physical data segments in a request.  This would be the largest sized
+ *    scatter list the driver could handle.
+ **/
+void blk_queue_max_phys_segments(struct request_queue *q,
+                                 unsigned short max_segments)
+{
+        if (!max_segments) {
+                max_segments = 1;
+                printk("%s: set to minimum %d\n", __FUNCTION__, max_segments);
+        }
+
+        q->max_phys_segments = max_segments;
+}
+
+EXPORT_SYMBOL(blk_queue_max_phys_segments);
+
+/**
+ * blk_queue_max_hw_segments - set max hw segments for a request for this queue
+ * @q:  the request queue for the device
+ * @max_segments:  max number of segments
+ *
+ * Description:
+ *    Enables a low level driver to set an upper limit on the number of
+ *    hw data segments in a request.  This would be the largest number of
+ *    address/length pairs the host adapter can actually give as once
+ *    to the device.
+ **/
+void blk_queue_max_hw_segments(struct request_queue *q,
+                               unsigned short max_segments)
+{
+        if (!max_segments) {
+                max_segments = 1;
+                printk("%s: set to minimum %d\n", __FUNCTION__, max_segments);
+        }
+
+        q->max_hw_segments = max_segments;
+}
+
+EXPORT_SYMBOL(blk_queue_max_hw_segments);
+
+/**
+ * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
+ * @q:  the request queue for the device
+ * @max_size:  max size of segment in bytes
+ *
+ * Description:
+ *    Enables a low level driver to set an upper limit on the size of a
+ *    coalesced segment
+ **/
+void blk_queue_max_segment_size(struct request_queue *q, unsigned int max_size)
+{
+        if (max_size < PAGE_CACHE_SIZE) {
+                max_size = PAGE_CACHE_SIZE;
+                printk("%s: set to minimum %d\n", __FUNCTION__, max_size);
+        }
+
+        q->max_segment_size = max_size;
+}
+
+EXPORT_SYMBOL(blk_queue_max_segment_size);
+
+/**
+ * blk_queue_hardsect_size - set hardware sector size for the queue
+ * @q:  the request queue for the device
+ * @size:  the hardware sector size, in bytes
+ *
+ * Description:
+ *   This should typically be set to the lowest possible sector size
+ *   that the hardware can operate on (possible without reverting to
+ *   even internal read-modify-write operations). Usually the default
+ *   of 512 covers most hardware.
+ **/
+void blk_queue_hardsect_size(struct request_queue *q, unsigned short size)
+{
+        q->hardsect_size = size;
+}
+
+EXPORT_SYMBOL(blk_queue_hardsect_size);
+
+/*
+ * Returns the minimum that is _not_ zero, unless both are zero.
+ */
+#define min_not_zero(l, r) (l == 0) ? r : ((r == 0) ? l : min(l, r))
+
+/**
+ * blk_queue_stack_limits - inherit underlying queue limits for stacked drivers
+ * @t:  the stacking driver (top)
+ * @b:  the underlying device (bottom)
+ **/
+void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
+{
+        /* zero is "infinity" */
+        t->max_sectors = min_not_zero(t->max_sectors,b->max_sectors);
+        t->max_hw_sectors = min_not_zero(t->max_hw_sectors,b->max_hw_sectors);
+
+        t->max_phys_segments = min(t->max_phys_segments,b->max_phys_segments);
+        t->max_hw_segments = min(t->max_hw_segments,b->max_hw_segments);
+        t->max_segment_size = min(t->max_segment_size,b->max_segment_size);
+        t->hardsect_size = max(t->hardsect_size,b->hardsect_size);
+        if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags))
+                clear_bit(QUEUE_FLAG_CLUSTER, &t->queue_flags);
+}
+
+EXPORT_SYMBOL(blk_queue_stack_limits);
+
+/**
+ * blk_queue_dma_drain - Set up a drain buffer for excess dma.
+ *
+ * @q:  the request queue for the device
+ * @buf:        physically contiguous buffer
+ * @size:       size of the buffer in bytes
+ *
+ * Some devices have excess DMA problems and can't simply discard (or
+ * zero fill) the unwanted piece of the transfer.  They have to have a
+ * real area of memory to transfer it into.  The use case for this is
+ * ATAPI devices in DMA mode.  If the packet command causes a transfer
+ * bigger than the transfer size some HBAs will lock up if there
+ * aren't DMA elements to contain the excess transfer.  What this API
+ * does is adjust the queue so that the buf is always appended
+ * silently to the scatterlist.
+ *
+ * Note: This routine adjusts max_hw_segments to make room for
+ * appending the drain buffer.  If you call
+ * blk_queue_max_hw_segments() or blk_queue_max_phys_segments() after
+ * calling this routine, you must set the limit to one fewer than your
+ * device can support otherwise there won't be room for the drain
+ * buffer.
+ */
+int blk_queue_dma_drain(struct request_queue *q, void *buf,
+                                unsigned int size)
+{
+        if (q->max_hw_segments < 2 || q->max_phys_segments < 2)
+                return -EINVAL;
+        /* make room for appending the drain */
+        --q->max_hw_segments;
+        --q->max_phys_segments;
+        q->dma_drain_buffer = buf;
+        q->dma_drain_size = size;
+
+        return 0;
+}
+
+EXPORT_SYMBOL_GPL(blk_queue_dma_drain);
+
+/**
+ * blk_queue_segment_boundary - set boundary rules for segment merging
+ * @q:  the request queue for the device
+ * @mask:  the memory boundary mask
+ **/
+void blk_queue_segment_boundary(struct request_queue *q, unsigned long mask)
+{
+        if (mask < PAGE_CACHE_SIZE - 1) {
+                mask = PAGE_CACHE_SIZE - 1;
+                printk("%s: set to minimum %lx\n", __FUNCTION__, mask);
+        }
+
+        q->seg_boundary_mask = mask;
+}
+
+EXPORT_SYMBOL(blk_queue_segment_boundary);
+
+/**
+ * blk_queue_dma_alignment - set dma length and memory alignment
+ * @q:     the request queue for the device
+ * @mask:  alignment mask
+ *
+ * description:
+ *    set required memory and length aligment for direct dma transactions.
+ *    this is used when buiding direct io requests for the queue.
+ *
+ **/
+void blk_queue_dma_alignment(struct request_queue *q, int mask)
+{
+        q->dma_alignment = mask;
+}
+
+EXPORT_SYMBOL(blk_queue_dma_alignment);
+
+/**
+ * blk_queue_update_dma_alignment - update dma length and memory alignment
+ * @q:     the request queue for the device
+ * @mask:  alignment mask
+ *
+ * description:
+ *    update required memory and length aligment for direct dma transactions.
+ *    If the requested alignment is larger than the current alignment, then
+ *    the current queue alignment is updated to the new value, otherwise it
+ *    is left alone.  The design of this is to allow multiple objects
+ *    (driver, device, transport etc) to set their respective
+ *    alignments without having them interfere.
+ *
+ **/
+void blk_queue_update_dma_alignment(struct request_queue *q, int mask)
+{
+        BUG_ON(mask > PAGE_SIZE);
+
+        if (mask > q->dma_alignment)
+                q->dma_alignment = mask;
+}
+
+EXPORT_SYMBOL(blk_queue_update_dma_alignment);
+
+/**
+ * blk_queue_find_tag - find a request by its tag and queue
+ * @q:   The request queue for the device
+ * @tag: The tag of the request
+ *
+ * Notes:
+ *    Should be used when a device returns a tag and you want to match
+ *    it with a request.
+ *
+ *    no locks need be held.
+ **/
+struct request *blk_queue_find_tag(struct request_queue *q, int tag)
+{
+        return blk_map_queue_find_tag(q->queue_tags, tag);
+}
+
+EXPORT_SYMBOL(blk_queue_find_tag);
+
+/**
+ * __blk_free_tags - release a given set of tag maintenance info
+ * @bqt:        the tag map to free
+ *
+ * Tries to free the specified @bqt@.  Returns true if it was
+ * actually freed and false if there are still references using it
+ */
+static int __blk_free_tags(struct blk_queue_tag *bqt)
+{
+        int retval;
+
+        retval = atomic_dec_and_test(&bqt->refcnt);
+        if (retval) {
+                BUG_ON(bqt->busy);
+
+                kfree(bqt->tag_index);
+                bqt->tag_index = NULL;
+
+                kfree(bqt->tag_map);
+                bqt->tag_map = NULL;
+
+                kfree(bqt);
+
+        }
+
+        return retval;
+}
+
+/**
+ * __blk_queue_free_tags - release tag maintenance info
+ * @q:  the request queue for the device
+ *
+ *  Notes:
+ *    blk_cleanup_queue() will take care of calling this function, if tagging
+ *    has been used. So there's no need to call this directly.
+ **/
+static void __blk_queue_free_tags(struct request_queue *q)
+{
+        struct blk_queue_tag *bqt = q->queue_tags;
+
+        if (!bqt)
+                return;
+
+        __blk_free_tags(bqt);
+
+        q->queue_tags = NULL;
+        q->queue_flags &= ~(1 << QUEUE_FLAG_QUEUED);
+}
+
+
+/**
+ * blk_free_tags - release a given set of tag maintenance info
+ * @bqt:        the tag map to free
+ *
+ * For externally managed @bqt@ frees the map.  Callers of this
+ * function must guarantee to have released all the queues that
+ * might have been using this tag map.
+ */
+void blk_free_tags(struct blk_queue_tag *bqt)
+{
+        if (unlikely(!__blk_free_tags(bqt)))
+                BUG();
+}
+EXPORT_SYMBOL(blk_free_tags);
+
+/**
+ * blk_queue_free_tags - release tag maintenance info
+ * @q:  the request queue for the device
+ *
+ *  Notes:
+ *      This is used to disabled tagged queuing to a device, yet leave
+ *      queue in function.
+ **/
+void blk_queue_free_tags(struct request_queue *q)
+{
+        clear_bit(QUEUE_FLAG_QUEUED, &q->queue_flags);
+}
+
+EXPORT_SYMBOL(blk_queue_free_tags);
+
+static int
+init_tag_map(struct request_queue *q, struct blk_queue_tag *tags, int depth)
+{
+        struct request **tag_index;
+        unsigned long *tag_map;
+        int nr_ulongs;
+
+        if (q && depth > q->nr_requests * 2) {
+                depth = q->nr_requests * 2;
+                printk(KERN_ERR "%s: adjusted depth to %d\n",
+                                __FUNCTION__, depth);
+        }
+
+        tag_index = kzalloc(depth * sizeof(struct request *), GFP_ATOMIC);
+        if (!tag_index)
+                goto fail;
+
+        nr_ulongs = ALIGN(depth, BITS_PER_LONG) / BITS_PER_LONG;
+        tag_map = kzalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
+        if (!tag_map)
+                goto fail;
+
+        tags->real_max_depth = depth;
+        tags->max_depth = depth;
+        tags->tag_index = tag_index;
+        tags->tag_map = tag_map;
+
+        return 0;
+fail:
+        kfree(tag_index);
+        return -ENOMEM;
+}
+
+static struct blk_queue_tag *__blk_queue_init_tags(struct request_queue *q,
+                                                   int depth)
+{
+        struct blk_queue_tag *tags;
+
+        tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
+        if (!tags)
+                goto fail;
+
+        if (init_tag_map(q, tags, depth))
+                goto fail;
+
+        tags->busy = 0;
+        atomic_set(&tags->refcnt, 1);
+        return tags;
+fail:
+        kfree(tags);
+        return NULL;
+}
+
+/**
+ * blk_init_tags - initialize the tag info for an external tag map
+ * @depth:      the maximum queue depth supported
+ * @tags: the tag to use
+ **/
+struct blk_queue_tag *blk_init_tags(int depth)
+{
+        return __blk_queue_init_tags(NULL, depth);
+}
+EXPORT_SYMBOL(blk_init_tags);
+
+/**
+ * blk_queue_init_tags - initialize the queue tag info
+ * @q:  the request queue for the device
+ * @depth:  the maximum queue depth supported
+ * @tags: the tag to use
+ **/
+int blk_queue_init_tags(struct request_queue *q, int depth,
+                        struct blk_queue_tag *tags)
+{
+        int rc;
+
+        BUG_ON(tags && q->queue_tags && tags != q->queue_tags);
+
+        if (!tags && !q->queue_tags) {
+                tags = __blk_queue_init_tags(q, depth);
+
+                if (!tags)
+                        goto fail;
+        } else if (q->queue_tags) {
+                if ((rc = blk_queue_resize_tags(q, depth)))
+                        return rc;
+                set_bit(QUEUE_FLAG_QUEUED, &q->queue_flags);
+                return 0;
+        } else
+                atomic_inc(&tags->refcnt);
+
+        /*
+         * assign it, all done
+         */
+        q->queue_tags = tags;
+        q->queue_flags |= (1 << QUEUE_FLAG_QUEUED);
+        INIT_LIST_HEAD(&q->tag_busy_list);
+        return 0;
+fail:
+        kfree(tags);
+        return -ENOMEM;
+}
+
+EXPORT_SYMBOL(blk_queue_init_tags);
+
+/**
+ * blk_queue_resize_tags - change the queueing depth
+ * @q:  the request queue for the device
+ * @new_depth: the new max command queueing depth
+ *
+ *  Notes:
+ *    Must be called with the queue lock held.
+ **/
+int blk_queue_resize_tags(struct request_queue *q, int new_depth)
+{
+        struct blk_queue_tag *bqt = q->queue_tags;
+        struct request **tag_index;
+        unsigned long *tag_map;
+        int max_depth, nr_ulongs;
+
+        if (!bqt)
+                return -ENXIO;
+
+        /*
+         * if we already have large enough real_max_depth.  just
+         * adjust max_depth.  *NOTE* as requests with tag value
+         * between new_depth and real_max_depth can be in-flight, tag
+         * map can not be shrunk blindly here.
+         */
+        if (new_depth <= bqt->real_max_depth) {
+                bqt->max_depth = new_depth;
+                return 0;
+        }
+
+        /*
+         * Currently cannot replace a shared tag map with a new
+         * one, so error out if this is the case
+         */
+        if (atomic_read(&bqt->refcnt) != 1)
+                return -EBUSY;
+
+        /*
+         * save the old state info, so we can copy it back
+         */
+        tag_index = bqt->tag_index;
+        tag_map = bqt->tag_map;
+        max_depth = bqt->real_max_depth;
+
+        if (init_tag_map(q, bqt, new_depth))
+                return -ENOMEM;
+
+        memcpy(bqt->tag_index, tag_index, max_depth * sizeof(struct request *));
+        nr_ulongs = ALIGN(max_depth, BITS_PER_LONG) / BITS_PER_LONG;
+        memcpy(bqt->tag_map, tag_map, nr_ulongs * sizeof(unsigned long));
+
+        kfree(tag_index);
+        kfree(tag_map);
+        return 0;
+}
+
+EXPORT_SYMBOL(blk_queue_resize_tags);
+
+/**
+ * blk_queue_end_tag - end tag operations for a request
+ * @q:  the request queue for the device
+ * @rq: the request that has completed
+ *
+ *  Description:
+ *    Typically called when end_that_request_first() returns 0, meaning
+ *    all transfers have been done for a request. It's important to call
+ *    this function before end_that_request_last(), as that will put the
+ *    request back on the free list thus corrupting the internal tag list.
+ *
+ *  Notes:
+ *   queue lock must be held.
+ **/
+void blk_queue_end_tag(struct request_queue *q, struct request *rq)
+{
+        struct blk_queue_tag *bqt = q->queue_tags;
+        int tag = rq->tag;
+
+        BUG_ON(tag == -1);
+
+        if (unlikely(tag >= bqt->real_max_depth))
+                /*
+                 * This can happen after tag depth has been reduced.
+                 * FIXME: how about a warning or info message here?
+                 */
+                return;
+
+        list_del_init(&rq->queuelist);
+        rq->cmd_flags &= ~REQ_QUEUED;
+        rq->tag = -1;
+
+        if (unlikely(bqt->tag_index[tag] == NULL))
+                printk(KERN_ERR "%s: tag %d is missing\n",
+                       __FUNCTION__, tag);
+
+        bqt->tag_index[tag] = NULL;
+
+        if (unlikely(!test_bit(tag, bqt->tag_map))) {
+                printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
+                       __FUNCTION__, tag);
+                return;
+        }
+        /*
+         * The tag_map bit acts as a lock for tag_index[bit], so we need
+         * unlock memory barrier semantics.
+         */
+        clear_bit_unlock(tag, bqt->tag_map);
+        bqt->busy--;
+}
+
+EXPORT_SYMBOL(blk_queue_end_tag);
+
+/**
+ * blk_queue_start_tag - find a free tag and assign it
+ * @q:  the request queue for the device
+ * @rq:  the block request that needs tagging
+ *
+ *  Description:
+ *    This can either be used as a stand-alone helper, or possibly be
+ *    assigned as the queue &prep_rq_fn (in which case &struct request
+ *    automagically gets a tag assigned). Note that this function
+ *    assumes that any type of request can be queued! if this is not
+ *    true for your device, you must check the request type before
+ *    calling this function.  The request will also be removed from
+ *    the request queue, so it's the drivers responsibility to readd
+ *    it if it should need to be restarted for some reason.
+ *
+ *  Notes:
+ *   queue lock must be held.
+ **/
+int blk_queue_start_tag(struct request_queue *q, struct request *rq)
+{
+        struct blk_queue_tag *bqt = q->queue_tags;
+        int tag;
+
+        if (unlikely((rq->cmd_flags & REQ_QUEUED))) {
+                printk(KERN_ERR 
+                       "%s: request %p for device [%s] already tagged %d",
+                       __FUNCTION__, rq,
+                       rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->tag);
+                BUG();
+        }
+
+        /*
+         * Protect against shared tag maps, as we may not have exclusive
+         * access to the tag map.
+         */
+        do {
+                tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth);
+                if (tag >= bqt->max_depth)
+                        return 1;
+
+        } while (test_and_set_bit_lock(tag, bqt->tag_map));
+        /*
+         * We need lock ordering semantics given by test_and_set_bit_lock.
+         * See blk_queue_end_tag for details.
+         */
+
+        rq->cmd_flags |= REQ_QUEUED;
+        rq->tag = tag;
+        bqt->tag_index[tag] = rq;
+        blkdev_dequeue_request(rq);
+        list_add(&rq->queuelist, &q->tag_busy_list);
+        bqt->busy++;
+        return 0;
+}
+
+EXPORT_SYMBOL(blk_queue_start_tag);
+
+/**
+ * blk_queue_invalidate_tags - invalidate all pending tags
+ * @q:  the request queue for the device
+ *
+ *  Description:
+ *   Hardware conditions may dictate a need to stop all pending requests.
+ *   In this case, we will safely clear the block side of the tag queue and
+ *   readd all requests to the request queue in the right order.
+ *
+ *  Notes:
+ *   queue lock must be held.
+ **/
+void blk_queue_invalidate_tags(struct request_queue *q)
+{
+        struct list_head *tmp, *n;
+
+        list_for_each_safe(tmp, n, &q->tag_busy_list)
+                blk_requeue_request(q, list_entry_rq(tmp));
+}
+
+EXPORT_SYMBOL(blk_queue_invalidate_tags);
+
+void blk_dump_rq_flags(struct request *rq, char *msg)
+{
+        int bit;
+
+        printk("%s: dev %s: type=%x, flags=%x\n", msg,
+                rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->cmd_type,
+                rq->cmd_flags);
+
+        printk("\nsector %llu, nr/cnr %lu/%u\n", (unsigned long long)rq->sector,
+                                                       rq->nr_sectors,
+                                                       rq->current_nr_sectors);
+        printk("bio %p, biotail %p, buffer %p, data %p, len %u\n", rq->bio, rq->biotail, rq->buffer, rq->data, rq->data_len);
+
+        if (blk_pc_request(rq)) {
+                printk("cdb: ");
+                for (bit = 0; bit < sizeof(rq->cmd); bit++)
+                        printk("%02x ", rq->cmd[bit]);
+                printk("\n");
+        }
+}
+
+EXPORT_SYMBOL(blk_dump_rq_flags);
+
+void blk_recount_segments(struct request_queue *q, struct bio *bio)
+{
+        struct request rq;
+        struct bio *nxt = bio->bi_next;
+        rq.q = q;
+        rq.bio = rq.biotail = bio;
+        bio->bi_next = NULL;
+        blk_recalc_rq_segments(&rq);
+        bio->bi_next = nxt;
+        bio->bi_phys_segments = rq.nr_phys_segments;
+        bio->bi_hw_segments = rq.nr_hw_segments;
+        bio->bi_flags |= (1 << BIO_SEG_VALID);
+}
+EXPORT_SYMBOL(blk_recount_segments);
+
+static void blk_recalc_rq_segments(struct request *rq)
+{
+        int nr_phys_segs;
+        int nr_hw_segs;
+        unsigned int phys_size;
+        unsigned int hw_size;
+        struct bio_vec *bv, *bvprv = NULL;
+        int seg_size;
+        int hw_seg_size;
+        int cluster;
+        struct req_iterator iter;
+        int high, highprv = 1;
+        struct request_queue *q = rq->q;
+
+        if (!rq->bio)
+                return;
+
+        cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+        hw_seg_size = seg_size = 0;
+        phys_size = hw_size = nr_phys_segs = nr_hw_segs = 0;
+        rq_for_each_segment(bv, rq, iter) {
+                /*
+                 * the trick here is making sure that a high page is never
+                 * considered part of another segment, since that might
+                 * change with the bounce page.
+                 */
+                high = page_to_pfn(bv->bv_page) > q->bounce_pfn;
+                if (high || highprv)
+                        goto new_hw_segment;
+                if (cluster) {
+                        if (seg_size + bv->bv_len > q->max_segment_size)
+                                goto new_segment;
+                        if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
+                                goto new_segment;
+                        if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
+                                goto new_segment;
+                        if (BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
+                                goto new_hw_segment;
+
+                        seg_size += bv->bv_len;
+                        hw_seg_size += bv->bv_len;
+                        bvprv = bv;
+                        continue;
+                }
+new_segment:
+                if (BIOVEC_VIRT_MERGEABLE(bvprv, bv) &&
+                    !BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
+                        hw_seg_size += bv->bv_len;
+                else {
+new_hw_segment:
+                        if (nr_hw_segs == 1 &&
+                            hw_seg_size > rq->bio->bi_hw_front_size)
+                                rq->bio->bi_hw_front_size = hw_seg_size;
+                        hw_seg_size = BIOVEC_VIRT_START_SIZE(bv) + bv->bv_len;
+                        nr_hw_segs++;
+                }
+
+                nr_phys_segs++;
+                bvprv = bv;
+                seg_size = bv->bv_len;
+                highprv = high;
+        }
+
+        if (nr_hw_segs == 1 &&
+            hw_seg_size > rq->bio->bi_hw_front_size)
+                rq->bio->bi_hw_front_size = hw_seg_size;
+        if (hw_seg_size > rq->biotail->bi_hw_back_size)
+                rq->biotail->bi_hw_back_size = hw_seg_size;
+        rq->nr_phys_segments = nr_phys_segs;
+        rq->nr_hw_segments = nr_hw_segs;
+}
+
+static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
+                                   struct bio *nxt)
+{
+        if (!(q->queue_flags & (1 << QUEUE_FLAG_CLUSTER)))
+                return 0;
+
+        if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
+                return 0;
+        if (bio->bi_size + nxt->bi_size > q->max_segment_size)
+                return 0;
+
+        /*
+         * bio and nxt are contigous in memory, check if the queue allows
+         * these two to be merged into one
+         */
+        if (BIO_SEG_BOUNDARY(q, bio, nxt))
+                return 1;
+
+        return 0;
+}
+
+static int blk_hw_contig_segment(struct request_queue *q, struct bio *bio,
+                                 struct bio *nxt)
+{
+        if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+                blk_recount_segments(q, bio);
+        if (unlikely(!bio_flagged(nxt, BIO_SEG_VALID)))
+                blk_recount_segments(q, nxt);
+        if (!BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)) ||
+            BIOVEC_VIRT_OVERSIZE(bio->bi_hw_back_size + nxt->bi_hw_front_size))
+                return 0;
+        if (bio->bi_hw_back_size + nxt->bi_hw_front_size > q->max_segment_size)
+                return 0;
+
+        return 1;
+}
+
+/*
+ * map a request to scatterlist, return number of sg entries setup. Caller
+ * must make sure sg can hold rq->nr_phys_segments entries
+ */
+int blk_rq_map_sg(struct request_queue *q, struct request *rq,
+                  struct scatterlist *sglist)
+{
+        struct bio_vec *bvec, *bvprv;
+        struct req_iterator iter;
+        struct scatterlist *sg;
+        int nsegs, cluster;
+
+        nsegs = 0;
+        cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+
+        /*
+         * for each bio in rq
+         */
+        bvprv = NULL;
+        sg = NULL;
+        rq_for_each_segment(bvec, rq, iter) {
+                int nbytes = bvec->bv_len;
+
+                if (bvprv && cluster) {
+                        if (sg->length + nbytes > q->max_segment_size)
+                                goto new_segment;
+
+                        if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
+                                goto new_segment;
+                        if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
+                                goto new_segment;
+
+                        sg->length += nbytes;
+                } else {
+new_segment:
+                        if (!sg)
+                                sg = sglist;
+                        else {
+                                /*
+                                 * If the driver previously mapped a shorter
+                                 * list, we could see a termination bit
+                                 * prematurely unless it fully inits the sg
+                                 * table on each mapping. We KNOW that there
+                                 * must be more entries here or the driver
+                                 * would be buggy, so force clear the
+                                 * termination bit to avoid doing a full
+                                 * sg_init_table() in drivers for each command.
+                                 */
+                                sg->page_link &= ~0x02;
+                                sg = sg_next(sg);
+                        }
+
+                        sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
+                        nsegs++;
+                }
+                bvprv = bvec;
+        } /* segments in rq */
+
+        if (q->dma_drain_size) {
+                sg->page_link &= ~0x02;
+                sg = sg_next(sg);
+                sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
+                            q->dma_drain_size,
+                            ((unsigned long)q->dma_drain_buffer) &
+                            (PAGE_SIZE - 1));
+                nsegs++;
+        }
+
+        if (sg)
+                sg_mark_end(sg);
+
+        return nsegs;
+}
+
+EXPORT_SYMBOL(blk_rq_map_sg);
+
+/*
+ * the standard queue merge functions, can be overridden with device
+ * specific ones if so desired
+ */
+
+static inline int ll_new_mergeable(struct request_queue *q,
+                                   struct request *req,
+                                   struct bio *bio)
+{
+        int nr_phys_segs = bio_phys_segments(q, bio);
+
+        if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
+                req->cmd_flags |= REQ_NOMERGE;
+                if (req == q->last_merge)
+                        q->last_merge = NULL;
+                return 0;
+        }
+
+        /*
+         * A hw segment is just getting larger, bump just the phys
+         * counter.
+         */
+        req->nr_phys_segments += nr_phys_segs;
+        return 1;
+}
+
+static inline int ll_new_hw_segment(struct request_queue *q,
+                                    struct request *req,
+                                    struct bio *bio)
+{
+        int nr_hw_segs = bio_hw_segments(q, bio);
+        int nr_phys_segs = bio_phys_segments(q, bio);
+
+        if (req->nr_hw_segments + nr_hw_segs > q->max_hw_segments
+            || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
+                req->cmd_flags |= REQ_NOMERGE;
+                if (req == q->last_merge)
+                        q->last_merge = NULL;
+                return 0;
+        }
+
+        /*
+         * This will form the start of a new hw segment.  Bump both
+         * counters.
+         */
+        req->nr_hw_segments += nr_hw_segs;
+        req->nr_phys_segments += nr_phys_segs;
+        return 1;
+}
+
+static int ll_back_merge_fn(struct request_queue *q, struct request *req,
+                            struct bio *bio)
+{
+        unsigned short max_sectors;
+        int len;
+
+        if (unlikely(blk_pc_request(req)))
+                max_sectors = q->max_hw_sectors;
+        else
+                max_sectors = q->max_sectors;
+
+        if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
+                req->cmd_flags |= REQ_NOMERGE;
+                if (req == q->last_merge)
+                        q->last_merge = NULL;
+                return 0;
+        }
+        if (unlikely(!bio_flagged(req->biotail, BIO_SEG_VALID)))
+                blk_recount_segments(q, req->biotail);
+        if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+                blk_recount_segments(q, bio);
+        len = req->biotail->bi_hw_back_size + bio->bi_hw_front_size;
+        if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio)) &&
+            !BIOVEC_VIRT_OVERSIZE(len)) {
+                int mergeable =  ll_new_mergeable(q, req, bio);
+
+                if (mergeable) {
+                        if (req->nr_hw_segments == 1)
+                                req->bio->bi_hw_front_size = len;
+                        if (bio->bi_hw_segments == 1)
+                                bio->bi_hw_back_size = len;
+                }
+                return mergeable;
+        }
+
+        return ll_new_hw_segment(q, req, bio);
+}
+
+static int ll_front_merge_fn(struct request_queue *q, struct request *req, 
+                             struct bio *bio)
+{
+        unsigned short max_sectors;
+        int len;
+
+        if (unlikely(blk_pc_request(req)))
+                max_sectors = q->max_hw_sectors;
+        else
+                max_sectors = q->max_sectors;
+
+
+        if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
+                req->cmd_flags |= REQ_NOMERGE;
+                if (req == q->last_merge)
+                        q->last_merge = NULL;
+                return 0;
+        }
+        len = bio->bi_hw_back_size + req->bio->bi_hw_front_size;
+        if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+                blk_recount_segments(q, bio);
+        if (unlikely(!bio_flagged(req->bio, BIO_SEG_VALID)))
+                blk_recount_segments(q, req->bio);
+        if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) &&
+            !BIOVEC_VIRT_OVERSIZE(len)) {
+                int mergeable =  ll_new_mergeable(q, req, bio);
+
+                if (mergeable) {
+                        if (bio->bi_hw_segments == 1)
+                                bio->bi_hw_front_size = len;
+                        if (req->nr_hw_segments == 1)
+                                req->biotail->bi_hw_back_size = len;
+                }
+                return mergeable;
+        }
+
+        return ll_new_hw_segment(q, req, bio);
+}
+
+static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
+                                struct request *next)
+{
+        int total_phys_segments;
+        int total_hw_segments;
+
+        /*
+         * First check if the either of the requests are re-queued
+         * requests.  Can't merge them if they are.
+         */
+        if (req->special || next->special)
+                return 0;
+
+        /*
+         * Will it become too large?
+         */
+        if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
+                return 0;
+
+        total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
+        if (blk_phys_contig_segment(q, req->biotail, next->bio))
+                total_phys_segments--;
+
+        if (total_phys_segments > q->max_phys_segments)
+                return 0;
+
+        total_hw_segments = req->nr_hw_segments + next->nr_hw_segments;
+        if (blk_hw_contig_segment(q, req->biotail, next->bio)) {
+                int len = req->biotail->bi_hw_back_size + next->bio->bi_hw_front_size;
+                /*
+                 * propagate the combined length to the end of the requests
+                 */
+                if (req->nr_hw_segments == 1)
+                        req->bio->bi_hw_front_size = len;
+                if (next->nr_hw_segments == 1)
+                        next->biotail->bi_hw_back_size = len;
+                total_hw_segments--;
+        }
+
+        if (total_hw_segments > q->max_hw_segments)
+                return 0;
+
+        /* Merge is OK... */
+        req->nr_phys_segments = total_phys_segments;
+        req->nr_hw_segments = total_hw_segments;
+        return 1;
+}
+
+/*
+ * "plug" the device if there are no outstanding requests: this will
+ * force the transfer to start only after we have put all the requests
+ * on the list.
+ *
+ * This is called with interrupts off and no requests on the queue and
+ * with the queue lock held.
+ */
+void blk_plug_device(struct request_queue *q)
+{
+        WARN_ON(!irqs_disabled());
+
+        /*
+         * don't plug a stopped queue, it must be paired with blk_start_queue()
+         * which will restart the queueing
+         */
+        if (blk_queue_stopped(q))
+                return;
+
+        if (!test_and_set_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags)) {
+                mod_timer(&q->unplug_timer, jiffies + q->unplug_delay);
+                blk_add_trace_generic(q, NULL, 0, BLK_TA_PLUG);
+        }
+}
+
+EXPORT_SYMBOL(blk_plug_device);
+
+/*
+ * remove the queue from the plugged list, if present. called with
+ * queue lock held and interrupts disabled.
+ */
+int blk_remove_plug(struct request_queue *q)
+{
+        WARN_ON(!irqs_disabled());
+
+        if (!test_and_clear_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags))
+                return 0;
+
+        del_timer(&q->unplug_timer);
+        return 1;
+}
+
+EXPORT_SYMBOL(blk_remove_plug);
+
+/*
+ * remove the plug and let it rip..
+ */
+void __generic_unplug_device(struct request_queue *q)
+{
+        if (unlikely(blk_queue_stopped(q)))
+                return;
+
+        if (!blk_remove_plug(q))
+                return;
+
+        q->request_fn(q);
+}
+EXPORT_SYMBOL(__generic_unplug_device);
+
+/**
+ * generic_unplug_device - fire a request queue
+ * @q:    The &struct request_queue in question
+ *
+ * Description:
+ *   Linux uses plugging to build bigger requests queues before letting
+ *   the device have at them. If a queue is plugged, the I/O scheduler
+ *   is still adding and merging requests on the queue. Once the queue
+ *   gets unplugged, the request_fn defined for the queue is invoked and
+ *   transfers started.
+ **/
+void generic_unplug_device(struct request_queue *q)
+{
+        spin_lock_irq(q->queue_lock);
+        __generic_unplug_device(q);
+        spin_unlock_irq(q->queue_lock);
+}
+EXPORT_SYMBOL(generic_unplug_device);
+
+static void blk_backing_dev_unplug(struct backing_dev_info *bdi,
+                                   struct page *page)
+{
+        struct request_queue *q = bdi->unplug_io_data;
+
+        blk_unplug(q);
+}
+
+static void blk_unplug_work(struct work_struct *work)
+{
+        struct request_queue *q =
+                container_of(work, struct request_queue, unplug_work);
+
+        blk_add_trace_pdu_int(q, BLK_TA_UNPLUG_IO, NULL,
+                                q->rq.count[READ] + q->rq.count[WRITE]);
+
+        q->unplug_fn(q);
+}
+
+static void blk_unplug_timeout(unsigned long data)
+{
+        struct request_queue *q = (struct request_queue *)data;
+
+        blk_add_trace_pdu_int(q, BLK_TA_UNPLUG_TIMER, NULL,
+                                q->rq.count[READ] + q->rq.count[WRITE]);
+
+        kblockd_schedule_work(&q->unplug_work);
+}
+
+void blk_unplug(struct request_queue *q)
+{
+        /*
+         * devices don't necessarily have an ->unplug_fn defined
+         */
+        if (q->unplug_fn) {
+                blk_add_trace_pdu_int(q, BLK_TA_UNPLUG_IO, NULL,
+                                        q->rq.count[READ] + q->rq.count[WRITE]);
+
+                q->unplug_fn(q);
+        }
+}
+EXPORT_SYMBOL(blk_unplug);
+
+/**
+ * blk_start_queue - restart a previously stopped queue
+ * @q:    The &struct request_queue in question
+ *
+ * Description:
+ *   blk_start_queue() will clear the stop flag on the queue, and call
+ *   the request_fn for the queue if it was in a stopped state when
+ *   entered. Also see blk_stop_queue(). Queue lock must be held.
+ **/
+void blk_start_queue(struct request_queue *q)
+{
+        WARN_ON(!irqs_disabled());
+
+        clear_bit(QUEUE_FLAG_STOPPED, &q->queue_flags);
+
+        /*
+         * one level of recursion is ok and is much faster than kicking
+         * the unplug handling
+         */
+        if (!test_and_set_bit(QUEUE_FLAG_REENTER, &q->queue_flags)) {
+                q->request_fn(q);
+                clear_bit(QUEUE_FLAG_REENTER, &q->queue_flags);
+        } else {
+                blk_plug_device(q);
+                kblockd_schedule_work(&q->unplug_work);
+        }
+}
+
+EXPORT_SYMBOL(blk_start_queue);
+
+/**
+ * blk_stop_queue - stop a queue
+ * @q:    The &struct request_queue in question
+ *
+ * Description:
+ *   The Linux block layer assumes that a block driver will consume all
+ *   entries on the request queue when the request_fn strategy is called.
+ *   Often this will not happen, because of hardware limitations (queue
+ *   depth settings). If a device driver gets a 'queue full' response,
+ *   or if it simply chooses not to queue more I/O at one point, it can
+ *   call this function to prevent the request_fn from being called until
+ *   the driver has signalled it's ready to go again. This happens by calling
+ *   blk_start_queue() to restart queue operations. Queue lock must be held.
+ **/
+void blk_stop_queue(struct request_queue *q)
+{
+        blk_remove_plug(q);
+        set_bit(QUEUE_FLAG_STOPPED, &q->queue_flags);
+}
+EXPORT_SYMBOL(blk_stop_queue);
+
+/**
+ * blk_sync_queue - cancel any pending callbacks on a queue
+ * @q: the queue
+ *
+ * Description:
+ *     The block layer may perform asynchronous callback activity
+ *     on a queue, such as calling the unplug function after a timeout.
+ *     A block device may call blk_sync_queue to ensure that any
+ *     such activity is cancelled, thus allowing it to release resources
+ *     that the callbacks might use. The caller must already have made sure
+ *     that its ->make_request_fn will not re-add plugging prior to calling
+ *     this function.
+ *
+ */
+void blk_sync_queue(struct request_queue *q)
+{
+        del_timer_sync(&q->unplug_timer);
+        kblockd_flush_work(&q->unplug_work);
+}
+EXPORT_SYMBOL(blk_sync_queue);
+
+/**
+ * blk_run_queue - run a single device queue
+ * @q:  The queue to run
+ */
+void blk_run_queue(struct request_queue *q)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(q->queue_lock, flags);
+        blk_remove_plug(q);
+
+        /*
+         * Only recurse once to avoid overrunning the stack, let the unplug
+         * handling reinvoke the handler shortly if we already got there.
+         */
+        if (!elv_queue_empty(q)) {
+                if (!test_and_set_bit(QUEUE_FLAG_REENTER, &q->queue_flags)) {
+                        q->request_fn(q);
+                        clear_bit(QUEUE_FLAG_REENTER, &q->queue_flags);
+                } else {
+                        blk_plug_device(q);
+                        kblockd_schedule_work(&q->unplug_work);
+                }
+        }
+
+        spin_unlock_irqrestore(q->queue_lock, flags);
+}
+EXPORT_SYMBOL(blk_run_queue);
+
+/**
+ * blk_cleanup_queue: - release a &struct request_queue when it is no longer needed
+ * @kobj:    the kobj belonging of the request queue to be released
+ *
+ * Description:
+ *     blk_cleanup_queue is the pair to blk_init_queue() or
+ *     blk_queue_make_request().  It should be called when a request queue is
+ *     being released; typically when a block device is being de-registered.
+ *     Currently, its primary task it to free all the &struct request
+ *     structures that were allocated to the queue and the queue itself.
+ *
+ * Caveat:
+ *     Hopefully the low level driver will have finished any
+ *     outstanding requests first...
+ **/
+static void blk_release_queue(struct kobject *kobj)
+{
+        struct request_queue *q =
+                container_of(kobj, struct request_queue, kobj);
+        struct request_list *rl = &q->rq;
+
+        blk_sync_queue(q);
+
+        if (rl->rq_pool)
+                mempool_destroy(rl->rq_pool);
+
+        if (q->queue_tags)
+                __blk_queue_free_tags(q);
+
+        blk_trace_shutdown(q);
+
+        bdi_destroy(&q->backing_dev_info);
+        kmem_cache_free(requestq_cachep, q);
+}
+
+void blk_put_queue(struct request_queue *q)
+{
+        kobject_put(&q->kobj);
+}
+EXPORT_SYMBOL(blk_put_queue);
+
+void blk_cleanup_queue(struct request_queue * q)
+{
+        mutex_lock(&q->sysfs_lock);
+        set_bit(QUEUE_FLAG_DEAD, &q->queue_flags);
+        mutex_unlock(&q->sysfs_lock);
+
+        if (q->elevator)
+                elevator_exit(q->elevator);
+
+        blk_put_queue(q);
+}
+
+EXPORT_SYMBOL(blk_cleanup_queue);
+
+static int blk_init_free_list(struct request_queue *q)
+{
+        struct request_list *rl = &q->rq;
+
+        rl->count[READ] = rl->count[WRITE] = 0;
+        rl->starved[READ] = rl->starved[WRITE] = 0;
+        rl->elvpriv = 0;
+        init_waitqueue_head(&rl->wait[READ]);
+        init_waitqueue_head(&rl->wait[WRITE]);
+
+        rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
+                                mempool_free_slab, request_cachep, q->node);
+
+        if (!rl->rq_pool)
+                return -ENOMEM;
+
+        return 0;
+}
+
+struct request_queue *blk_alloc_queue(gfp_t gfp_mask)
+{
+        return blk_alloc_queue_node(gfp_mask, -1);
+}
+EXPORT_SYMBOL(blk_alloc_queue);
+
+static struct kobj_type queue_ktype;
+
+struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
+{
+        struct request_queue *q;
+        int err;
+
+        q = kmem_cache_alloc_node(requestq_cachep,
+                                gfp_mask | __GFP_ZERO, node_id);
+        if (!q)
+                return NULL;
+
+        q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
+        q->backing_dev_info.unplug_io_data = q;
+        err = bdi_init(&q->backing_dev_info);
+        if (err) {
+                kmem_cache_free(requestq_cachep, q);
+                return NULL;
+        }
+
+        init_timer(&q->unplug_timer);
+
+        kobject_init(&q->kobj, &queue_ktype);
+
+        mutex_init(&q->sysfs_lock);
+
+        return q;
+}
+EXPORT_SYMBOL(blk_alloc_queue_node);
+
+/**
+ * blk_init_queue  - prepare a request queue for use with a block device
+ * @rfn:  The function to be called to process requests that have been
+ *        placed on the queue.
+ * @lock: Request queue spin lock
+ *
+ * Description:
+ *    If a block device wishes to use the standard request handling procedures,
+ *    which sorts requests and coalesces adjacent requests, then it must
+ *    call blk_init_queue().  The function @rfn will be called when there
+ *    are requests on the queue that need to be processed.  If the device
+ *    supports plugging, then @rfn may not be called immediately when requests
+ *    are available on the queue, but may be called at some time later instead.
+ *    Plugged queues are generally unplugged when a buffer belonging to one
+ *    of the requests on the queue is needed, or due to memory pressure.
+ *
+ *    @rfn is not required, or even expected, to remove all requests off the
+ *    queue, but only as many as it can handle at a time.  If it does leave
+ *    requests on the queue, it is responsible for arranging that the requests
+ *    get dealt with eventually.
+ *
+ *    The queue spin lock must be held while manipulating the requests on the
+ *    request queue; this lock will be taken also from interrupt context, so irq
+ *    disabling is needed for it.
+ *
+ *    Function returns a pointer to the initialized request queue, or NULL if
+ *    it didn't succeed.
+ *
+ * Note:
+ *    blk_init_queue() must be paired with a blk_cleanup_queue() call
+ *    when the block device is deactivated (such as at module unload).
+ **/
+
+struct request_queue *blk_init_queue(request_fn_proc *rfn, spinlock_t *lock)
+{
+        return blk_init_queue_node(rfn, lock, -1);
+}
+EXPORT_SYMBOL(blk_init_queue);
+
+struct request_queue *
+blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
+{
+        struct request_queue *q = blk_alloc_queue_node(GFP_KERNEL, node_id);
+
+        if (!q)
+                return NULL;
+
+        q->node = node_id;
+        if (blk_init_free_list(q)) {
+                kmem_cache_free(requestq_cachep, q);
+                return NULL;
+        }
+
+        /*
+         * if caller didn't supply a lock, they get per-queue locking with
+         * our embedded lock
+         */
+        if (!lock) {
+                spin_lock_init(&q->__queue_lock);
+                lock = &q->__queue_lock;
+        }
+
+        q->request_fn           = rfn;
+        q->prep_rq_fn           = NULL;
+        q->unplug_fn            = generic_unplug_device;
+        q->queue_flags          = (1 << QUEUE_FLAG_CLUSTER);
+        q->queue_lock           = lock;
+
+        blk_queue_segment_boundary(q, 0xffffffff);
+
+        blk_queue_make_request(q, __make_request);
+        blk_queue_max_segment_size(q, MAX_SEGMENT_SIZE);
+
+        blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
+        blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
+
+        q->sg_reserved_size = INT_MAX;
+
+        /*
+         * all done
+         */
+        if (!elevator_init(q, NULL)) {
+                blk_queue_congestion_threshold(q);
+                return q;
+        }
+
+        blk_put_queue(q);
+        return NULL;
+}
+EXPORT_SYMBOL(blk_init_queue_node);
+
+int blk_get_queue(struct request_queue *q)
+{
+        if (likely(!test_bit(QUEUE_FLAG_DEAD, &q->queue_flags))) {
+                kobject_get(&q->kobj);
+                return 0;
+        }
+
+        return 1;
+}
+
+EXPORT_SYMBOL(blk_get_queue);
+
+static inline void blk_free_request(struct request_queue *q, struct request *rq)
+{
+        if (rq->cmd_flags & REQ_ELVPRIV)
+                elv_put_request(q, rq);
+        mempool_free(rq, q->rq.rq_pool);
+}
+
+static struct request *
+blk_alloc_request(struct request_queue *q, int rw, int priv, gfp_t gfp_mask)
+{
+        struct request *rq = mempool_alloc(q->rq.rq_pool, gfp_mask);
+
+        if (!rq)
+                return NULL;
+
+        /*
+         * first three bits are identical in rq->cmd_flags and bio->bi_rw,
+         * see bio.h and blkdev.h
+         */
+        rq->cmd_flags = rw | REQ_ALLOCED;
+
+        if (priv) {
+                if (unlikely(elv_set_request(q, rq, gfp_mask))) {
+                        mempool_free(rq, q->rq.rq_pool);
+                        return NULL;
+                }
+                rq->cmd_flags |= REQ_ELVPRIV;
+        }
+
+        return rq;
+}
+
+/*
+ * ioc_batching returns true if the ioc is a valid batching request and
+ * should be given priority access to a request.
+ */
+static inline int ioc_batching(struct request_queue *q, struct io_context *ioc)
+{
+        if (!ioc)
+                return 0;
+
+        /*
+         * Make sure the process is able to allocate at least 1 request
+         * even if the batch times out, otherwise we could theoretically
+         * lose wakeups.
+         */
+        return ioc->nr_batch_requests == q->nr_batching ||
+                (ioc->nr_batch_requests > 0
+                && time_before(jiffies, ioc->last_waited + BLK_BATCH_TIME));
+}
+
+/*
+ * ioc_set_batching sets ioc to be a new "batcher" if it is not one. This
+ * will cause the process to be a "batcher" on all queues in the system. This
+ * is the behaviour we want though - once it gets a wakeup it should be given
+ * a nice run.
+ */
+static void ioc_set_batching(struct request_queue *q, struct io_context *ioc)
+{
+        if (!ioc || ioc_batching(q, ioc))
+                return;
+
+        ioc->nr_batch_requests = q->nr_batching;
+        ioc->last_waited = jiffies;
+}
+
+static void __freed_request(struct request_queue *q, int rw)
+{
+        struct request_list *rl = &q->rq;
+
+        if (rl->count[rw] < queue_congestion_off_threshold(q))
+                blk_clear_queue_congested(q, rw);
+
+        if (rl->count[rw] + 1 <= q->nr_requests) {
+                if (waitqueue_active(&rl->wait[rw]))
+                        wake_up(&rl->wait[rw]);
+
+                blk_clear_queue_full(q, rw);
+        }
+}
+
+/*
+ * A request has just been released.  Account for it, update the full and
+ * congestion status, wake up any waiters.   Called under q->queue_lock.
+ */
+static void freed_request(struct request_queue *q, int rw, int priv)
+{
+        struct request_list *rl = &q->rq;
+
+        rl->count[rw]--;
+        if (priv)
+                rl->elvpriv--;
+
+        __freed_request(q, rw);
+
+        if (unlikely(rl->starved[rw ^ 1]))
+                __freed_request(q, rw ^ 1);
+}
+
+#define blkdev_free_rq(list) list_entry((list)->next, struct request, queuelist)
+/*
+ * Get a free request, queue_lock must be held.
+ * Returns NULL on failure, with queue_lock held.
+ * Returns !NULL on success, with queue_lock *not held*.
+ */
+static struct request *get_request(struct request_queue *q, int rw_flags,
+                                   struct bio *bio, gfp_t gfp_mask)
+{
+        struct request *rq = NULL;
+        struct request_list *rl = &q->rq;
+        struct io_context *ioc = NULL;
+        const int rw = rw_flags & 0x01;
+        int may_queue, priv;
+
+        may_queue = elv_may_queue(q, rw_flags);
+        if (may_queue == ELV_MQUEUE_NO)
+                goto rq_starved;
+
+        if (rl->count[rw]+1 >= queue_congestion_on_threshold(q)) {
+                if (rl->count[rw]+1 >= q->nr_requests) {
+                        ioc = current_io_context(GFP_ATOMIC, q->node);
+                        /*
+                         * The queue will fill after this allocation, so set
+                         * it as full, and mark this process as "batching".
+                         * This process will be allowed to complete a batch of
+                         * requests, others will be blocked.
+                         */
+                        if (!blk_queue_full(q, rw)) {
+                                ioc_set_batching(q, ioc);
+                                blk_set_queue_full(q, rw);
+                        } else {
+                                if (may_queue != ELV_MQUEUE_MUST
+                                                && !ioc_batching(q, ioc)) {
+                                        /*
+                                         * The queue is full and the allocating
+                                         * process is not a "batcher", and not
+                                         * exempted by the IO scheduler
+                                         */
+                                        goto out;
+                                }
+                        }
+                }
+                blk_set_queue_congested(q, rw);
+        }
+
+        /*
+         * Only allow batching queuers to allocate up to 50% over the defined
+         * limit of requests, otherwise we could have thousands of requests
+         * allocated with any setting of ->nr_requests
+         */
+        if (rl->count[rw] >= (3 * q->nr_requests / 2))
+                goto out;
+
+        rl->count[rw]++;
+        rl->starved[rw] = 0;
+
+        priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+        if (priv)
+                rl->elvpriv++;
+
+        spin_unlock_irq(q->queue_lock);
+
+        rq = blk_alloc_request(q, rw_flags, priv, gfp_mask);
+        if (unlikely(!rq)) {
+                /*
+                 * Allocation failed presumably due to memory. Undo anything
+                 * we might have messed up.
+                 *
+                 * Allocating task should really be put onto the front of the
+                 * wait queue, but this is pretty rare.
+                 */
+                spin_lock_irq(q->queue_lock);
+                freed_request(q, rw, priv);
+
+                /*
+                 * in the very unlikely event that allocation failed and no
+                 * requests for this direction was pending, mark us starved
+                 * so that freeing of a request in the other direction will
+                 * notice us. another possible fix would be to split the
+                 * rq mempool into READ and WRITE
+                 */
+rq_starved:
+                if (unlikely(rl->count[rw] == 0))
+                        rl->starved[rw] = 1;
+
+                goto out;
+        }
+
+        /*
+         * ioc may be NULL here, and ioc_batching will be false. That's
+         * OK, if the queue is under the request limit then requests need
+         * not count toward the nr_batch_requests limit. There will always
+         * be some limit enforced by BLK_BATCH_TIME.
+         */
+        if (ioc_batching(q, ioc))
+                ioc->nr_batch_requests--;
+        
+        rq_init(q, rq);
+
+        blk_add_trace_generic(q, bio, rw, BLK_TA_GETRQ);
+out:
+        return rq;
+}
+
+/*
+ * No available requests for this queue, unplug the device and wait for some
+ * requests to become available.
+ *
+ * Called with q->queue_lock held, and returns with it unlocked.
+ */
+static struct request *get_request_wait(struct request_queue *q, int rw_flags,
+                                        struct bio *bio)
+{
+        const int rw = rw_flags & 0x01;
+        struct request *rq;
+
+        rq = get_request(q, rw_flags, bio, GFP_NOIO);
+        while (!rq) {
+                DEFINE_WAIT(wait);
+                struct request_list *rl = &q->rq;
+
+                prepare_to_wait_exclusive(&rl->wait[rw], &wait,
+                                TASK_UNINTERRUPTIBLE);
+
+                rq = get_request(q, rw_flags, bio, GFP_NOIO);
+
+                if (!rq) {
+                        struct io_context *ioc;
+
+                        blk_add_trace_generic(q, bio, rw, BLK_TA_SLEEPRQ);
+
+                        __generic_unplug_device(q);
+                        spin_unlock_irq(q->queue_lock);
+                        io_schedule();
+
+                        /*
+                         * After sleeping, we become a "batching" process and
+                         * will be able to allocate at least one request, and
+                         * up to a big batch of them for a small period time.
+                         * See ioc_batching, ioc_set_batching
+                         */
+                        ioc = current_io_context(GFP_NOIO, q->node);
+                        ioc_set_batching(q, ioc);
+
+                        spin_lock_irq(q->queue_lock);
+                }
+                finish_wait(&rl->wait[rw], &wait);
+        }
+
+        return rq;
+}
+
+struct request *blk_get_request(struct request_queue *q, int rw, gfp_t gfp_mask)
+{
+        struct request *rq;
+
+        BUG_ON(rw != READ && rw != WRITE);
+
+        spin_lock_irq(q->queue_lock);
+        if (gfp_mask & __GFP_WAIT) {
+                rq = get_request_wait(q, rw, NULL);
+        } else {
+                rq = get_request(q, rw, NULL, gfp_mask);
+                if (!rq)
+                        spin_unlock_irq(q->queue_lock);
+        }
+        /* q->queue_lock is unlocked at this point */
+
+        return rq;
+}
+EXPORT_SYMBOL(blk_get_request);
+
+/**
+ * blk_start_queueing - initiate dispatch of requests to device
+ * @q:          request queue to kick into gear
+ *
+ * This is basically a helper to remove the need to know whether a queue
+ * is plugged or not if someone just wants to initiate dispatch of requests
+ * for this queue.
+ *
+ * The queue lock must be held with interrupts disabled.
+ */
+void blk_start_queueing(struct request_queue *q)
+{
+        if (!blk_queue_plugged(q))
+                q->request_fn(q);
+        else
+                __generic_unplug_device(q);
+}
+EXPORT_SYMBOL(blk_start_queueing);
+
+/**
+ * blk_requeue_request - put a request back on queue
+ * @q:          request queue where request should be inserted
+ * @rq:         request to be inserted
+ *
+ * Description:
+ *    Drivers often keep queueing requests until the hardware cannot accept
+ *    more, when that condition happens we need to put the request back
+ *    on the queue. Must be called with queue lock held.
+ */
+void blk_requeue_request(struct request_queue *q, struct request *rq)
+{
+        blk_add_trace_rq(q, rq, BLK_TA_REQUEUE);
+
+        if (blk_rq_tagged(rq))
+                blk_queue_end_tag(q, rq);
+
+        elv_requeue_request(q, rq);
+}
+
+EXPORT_SYMBOL(blk_requeue_request);
+
+/**
+ * blk_insert_request - insert a special request in to a request queue
+ * @q:          request queue where request should be inserted
+ * @rq:         request to be inserted
+ * @at_head:    insert request at head or tail of queue
+ * @data:       private data
+ *
+ * Description:
+ *    Many block devices need to execute commands asynchronously, so they don't
+ *    block the whole kernel from preemption during request execution.  This is
+ *    accomplished normally by inserting aritficial requests tagged as
+ *    REQ_SPECIAL in to the corresponding request queue, and letting them be
+ *    scheduled for actual execution by the request queue.
+ *
+ *    We have the option of inserting the head or the tail of the queue.
+ *    Typically we use the tail for new ioctls and so forth.  We use the head
+ *    of the queue for things like a QUEUE_FULL message from a device, or a
+ *    host that is unable to accept a particular command.
+ */
+void blk_insert_request(struct request_queue *q, struct request *rq,
+                        int at_head, void *data)
+{
+        int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
+        unsigned long flags;
+
+        /*
+         * tell I/O scheduler that this isn't a regular read/write (ie it
+         * must not attempt merges on this) and that it acts as a soft
+         * barrier
+         */
+        rq->cmd_type = REQ_TYPE_SPECIAL;
+        rq->cmd_flags |= REQ_SOFTBARRIER;
+
+        rq->special = data;
+
+        spin_lock_irqsave(q->queue_lock, flags);
+
+        /*
+         * If command is tagged, release the tag
+         */
+        if (blk_rq_tagged(rq))
+                blk_queue_end_tag(q, rq);
+
+        drive_stat_acct(rq, 1);
+        __elv_add_request(q, rq, where, 0);
+        blk_start_queueing(q);
+        spin_unlock_irqrestore(q->queue_lock, flags);
+}
+
+EXPORT_SYMBOL(blk_insert_request);
+
+static int __blk_rq_unmap_user(struct bio *bio)
+{
+        int ret = 0;
+
+        if (bio) {
+                if (bio_flagged(bio, BIO_USER_MAPPED))
+                        bio_unmap_user(bio);
+                else
+                        ret = bio_uncopy_user(bio);
+        }
+
+        return ret;
+}
+
+int blk_rq_append_bio(struct request_queue *q, struct request *rq,
+                      struct bio *bio)
+{
+        if (!rq->bio)
+                blk_rq_bio_prep(q, rq, bio);
+        else if (!ll_back_merge_fn(q, rq, bio))
+                return -EINVAL;
+        else {
+                rq->biotail->bi_next = bio;
+                rq->biotail = bio;
+
+                rq->data_len += bio->bi_size;
+        }
+        return 0;
+}
+EXPORT_SYMBOL(blk_rq_append_bio);
+
+static int __blk_rq_map_user(struct request_queue *q, struct request *rq,
+                             void __user *ubuf, unsigned int len)
+{
+        unsigned long uaddr;
+        struct bio *bio, *orig_bio;
+        int reading, ret;
+
+        reading = rq_data_dir(rq) == READ;
+
+        /*
+         * if alignment requirement is satisfied, map in user pages for
+         * direct dma. else, set up kernel bounce buffers
+         */
+        uaddr = (unsigned long) ubuf;
+        if (!(uaddr & queue_dma_alignment(q)) && !(len & queue_dma_alignment(q)))
+                bio = bio_map_user(q, NULL, uaddr, len, reading);
+        else
+                bio = bio_copy_user(q, uaddr, len, reading);
+
+        if (IS_ERR(bio))
+                return PTR_ERR(bio);
+
+        orig_bio = bio;
+        blk_queue_bounce(q, &bio);
+
+        /*
+         * We link the bounce buffer in and could have to traverse it
+         * later so we have to get a ref to prevent it from being freed
+         */
+        bio_get(bio);
+
+        ret = blk_rq_append_bio(q, rq, bio);
+        if (!ret)
+                return bio->bi_size;
+
+        /* if it was boucned we must call the end io function */
+        bio_endio(bio, 0);
+        __blk_rq_unmap_user(orig_bio);
+        bio_put(bio);
+        return ret;
+}
+
+/**
+ * blk_rq_map_user - map user data to a request, for REQ_BLOCK_PC usage
+ * @q:          request queue where request should be inserted
+ * @rq:         request structure to fill
+ * @ubuf:       the user buffer
+ * @len:        length of user data
+ *
+ * Description:
+ *    Data will be mapped directly for zero copy io, if possible. Otherwise
+ *    a kernel bounce buffer is used.
+ *
+ *    A matching blk_rq_unmap_user() must be issued at the end of io, while
+ *    still in process context.
+ *
+ *    Note: The mapped bio may need to be bounced through blk_queue_bounce()
+ *    before being submitted to the device, as pages mapped may be out of
+ *    reach. It's the callers responsibility to make sure this happens. The
+ *    original bio must be passed back in to blk_rq_unmap_user() for proper
+ *    unmapping.
+ */
+int blk_rq_map_user(struct request_queue *q, struct request *rq,
+                    void __user *ubuf, unsigned long len)
+{
+        unsigned long bytes_read = 0;
+        struct bio *bio = NULL;
+        int ret;
+
+        if (len > (q->max_hw_sectors << 9))
+                return -EINVAL;
+        if (!len || !ubuf)
+                return -EINVAL;
+
+        while (bytes_read != len) {
+                unsigned long map_len, end, start;
+
+                map_len = min_t(unsigned long, len - bytes_read, BIO_MAX_SIZE);
+                end = ((unsigned long)ubuf + map_len + PAGE_SIZE - 1)
+                                                                >> PAGE_SHIFT;
+                start = (unsigned long)ubuf >> PAGE_SHIFT;
+
+                /*
+                 * A bad offset could cause us to require BIO_MAX_PAGES + 1
+                 * pages. If this happens we just lower the requested
+                 * mapping len by a page so that we can fit
+                 */
+                if (end - start > BIO_MAX_PAGES)
+                        map_len -= PAGE_SIZE;
+
+                ret = __blk_rq_map_user(q, rq, ubuf, map_len);
+                if (ret < 0)
+                        goto unmap_rq;
+                if (!bio)
+                        bio = rq->bio;
+                bytes_read += ret;
+                ubuf += ret;
+        }
+
+        rq->buffer = rq->data = NULL;
+        return 0;
+unmap_rq:
+        blk_rq_unmap_user(bio);
+        return ret;
+}
+
+EXPORT_SYMBOL(blk_rq_map_user);
+
+/**
+ * blk_rq_map_user_iov - map user data to a request, for REQ_BLOCK_PC usage
+ * @q:          request queue where request should be inserted
+ * @rq:         request to map data to
+ * @iov:        pointer to the iovec
+ * @iov_count:  number of elements in the iovec
+ * @len:        I/O byte count
+ *
+ * Description:
+ *    Data will be mapped directly for zero copy io, if possible. Otherwise
+ *    a kernel bounce buffer is used.
+ *
+ *    A matching blk_rq_unmap_user() must be issued at the end of io, while
+ *    still in process context.
+ *
+ *    Note: The mapped bio may need to be bounced through blk_queue_bounce()
+ *    before being submitted to the device, as pages mapped may be out of
+ *    reach. It's the callers responsibility to make sure this happens. The
+ *    original bio must be passed back in to blk_rq_unmap_user() for proper
+ *    unmapping.
+ */
+int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
+                        struct sg_iovec *iov, int iov_count, unsigned int len)
+{
+        struct bio *bio;
+
+        if (!iov || iov_count <= 0)
+                return -EINVAL;
+
+        /* we don't allow misaligned data like bio_map_user() does.  If the
+         * user is using sg, they're expected to know the alignment constraints
+         * and respect them accordingly */
+        bio = bio_map_user_iov(q, NULL, iov, iov_count, rq_data_dir(rq)== READ);
+        if (IS_ERR(bio))
+                return PTR_ERR(bio);
+
+        if (bio->bi_size != len) {
+                bio_endio(bio, 0);
+                bio_unmap_user(bio);
+                return -EINVAL;
+        }
+
+        bio_get(bio);
+        blk_rq_bio_prep(q, rq, bio);
+        rq->buffer = rq->data = NULL;
+        return 0;
+}
+
+EXPORT_SYMBOL(blk_rq_map_user_iov);
+
+/**
+ * blk_rq_unmap_user - unmap a request with user data
+ * @bio:               start of bio list
+ *
+ * Description:
+ *    Unmap a rq previously mapped by blk_rq_map_user(). The caller must
+ *    supply the original rq->bio from the blk_rq_map_user() return, since
+ *    the io completion may have changed rq->bio.
+ */
+int blk_rq_unmap_user(struct bio *bio)
+{
+        struct bio *mapped_bio;
+        int ret = 0, ret2;
+
+        while (bio) {
+                mapped_bio = bio;
+                if (unlikely(bio_flagged(bio, BIO_BOUNCED)))
+                        mapped_bio = bio->bi_private;
+
+                ret2 = __blk_rq_unmap_user(mapped_bio);
+                if (ret2 && !ret)
+                        ret = ret2;
+
+                mapped_bio = bio;
+                bio = bio->bi_next;
+                bio_put(mapped_bio);
+        }
+
+        return ret;
+}
+
+EXPORT_SYMBOL(blk_rq_unmap_user);
+
+/**
+ * blk_rq_map_kern - map kernel data to a request, for REQ_BLOCK_PC usage
+ * @q:          request queue where request should be inserted
+ * @rq:         request to fill
+ * @kbuf:       the kernel buffer
+ * @len:        length of user data
+ * @gfp_mask:   memory allocation flags
+ */
+int blk_rq_map_kern(struct request_queue *q, struct request *rq, void *kbuf,
+                    unsigned int len, gfp_t gfp_mask)
+{
+        struct bio *bio;
+
+        if (len > (q->max_hw_sectors << 9))
+                return -EINVAL;
+        if (!len || !kbuf)
+                return -EINVAL;
+
+        bio = bio_map_kern(q, kbuf, len, gfp_mask);
+        if (IS_ERR(bio))
+                return PTR_ERR(bio);
+
+        if (rq_data_dir(rq) == WRITE)
+                bio->bi_rw |= (1 << BIO_RW);
+
+        blk_rq_bio_prep(q, rq, bio);
+        blk_queue_bounce(q, &rq->bio);
+        rq->buffer = rq->data = NULL;
+        return 0;
+}
+
+EXPORT_SYMBOL(blk_rq_map_kern);
+
+/**
+ * blk_execute_rq_nowait - insert a request into queue for execution
+ * @q:          queue to insert the request in
+ * @bd_disk:    matching gendisk
+ * @rq:         request to insert
+ * @at_head:    insert request at head or tail of queue
+ * @done:       I/O completion handler
+ *
+ * Description:
+ *    Insert a fully prepared request at the back of the io scheduler queue
+ *    for execution.  Don't wait for completion.
+ */
+void blk_execute_rq_nowait(struct request_queue *q, struct gendisk *bd_disk,
+                           struct request *rq, int at_head,
+                           rq_end_io_fn *done)
+{
+        int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
+
+        rq->rq_disk = bd_disk;
+        rq->cmd_flags |= REQ_NOMERGE;
+        rq->end_io = done;
+        WARN_ON(irqs_disabled());
+        spin_lock_irq(q->queue_lock);
+        __elv_add_request(q, rq, where, 1);
+        __generic_unplug_device(q);
+        spin_unlock_irq(q->queue_lock);
+}
+EXPORT_SYMBOL_GPL(blk_execute_rq_nowait);
+
+/**
+ * blk_execute_rq - insert a request into queue for execution
+ * @q:          queue to insert the request in
+ * @bd_disk:    matching gendisk
+ * @rq:         request to insert
+ * @at_head:    insert request at head or tail of queue
+ *
+ * Description:
+ *    Insert a fully prepared request at the back of the io scheduler queue
+ *    for execution and wait for completion.
+ */
+int blk_execute_rq(struct request_queue *q, struct gendisk *bd_disk,
+                   struct request *rq, int at_head)
+{
+        DECLARE_COMPLETION_ONSTACK(wait);
+        char sense[SCSI_SENSE_BUFFERSIZE];
+        int err = 0;
+
+        /*
+         * we need an extra reference to the request, so we can look at
+         * it after io completion
+         */
+        rq->ref_count++;
+
+        if (!rq->sense) {
+                memset(sense, 0, sizeof(sense));
+                rq->sense = sense;
+                rq->sense_len = 0;
+        }
+
+        rq->end_io_data = &wait;
+        blk_execute_rq_nowait(q, bd_disk, rq, at_head, blk_end_sync_rq);
+        wait_for_completion(&wait);
+
+        if (rq->errors)
+                err = -EIO;
+
+        return err;
+}
+
+EXPORT_SYMBOL(blk_execute_rq);
+
+static void bio_end_empty_barrier(struct bio *bio, int err)
+{
+        if (err)
+                clear_bit(BIO_UPTODATE, &bio->bi_flags);
+
+        complete(bio->bi_private);
+}
+
+/**
+ * blkdev_issue_flush - queue a flush
+ * @bdev:       blockdev to issue flush for
+ * @error_sector:       error sector
+ *
+ * Description:
+ *    Issue a flush for the block device in question. Caller can supply
+ *    room for storing the error offset in case of a flush error, if they
+ *    wish to.  Caller must run wait_for_completion() on its own.
+ */
+int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector)
+{
+        DECLARE_COMPLETION_ONSTACK(wait);
+        struct request_queue *q;
+        struct bio *bio;
+        int ret;
+
+        if (bdev->bd_disk == NULL)
+                return -ENXIO;
+
+        q = bdev_get_queue(bdev);
+        if (!q)
+                return -ENXIO;
+
+        bio = bio_alloc(GFP_KERNEL, 0);
+        if (!bio)
+                return -ENOMEM;
+
+        bio->bi_end_io = bio_end_empty_barrier;
+        bio->bi_private = &wait;
+        bio->bi_bdev = bdev;
+        submit_bio(1 << BIO_RW_BARRIER, bio);
+
+        wait_for_completion(&wait);
+
+        /*
+         * The driver must store the error location in ->bi_sector, if
+         * it supports it. For non-stacked drivers, this should be copied
+         * from rq->sector.
+         */
+        if (error_sector)
+                *error_sector = bio->bi_sector;
+
+        ret = 0;
+        if (!bio_flagged(bio, BIO_UPTODATE))
+                ret = -EIO;
+
+        bio_put(bio);
+        return ret;
+}
+
+EXPORT_SYMBOL(blkdev_issue_flush);
+
+static void drive_stat_acct(struct request *rq, int new_io)
+{
+        int rw = rq_data_dir(rq);
+
+        if (!blk_fs_request(rq) || !rq->rq_disk)
+                return;
+
+        if (!new_io) {
+                __disk_stat_inc(rq->rq_disk, merges[rw]);
+        } else {
+                disk_round_stats(rq->rq_disk);
+                rq->rq_disk->in_flight++;
+        }
+}
+
+/*
+ * add-request adds a request to the linked list.
+ * queue lock is held and interrupts disabled, as we muck with the
+ * request queue list.
+ */
+static inline void add_request(struct request_queue * q, struct request * req)
+{
+        drive_stat_acct(req, 1);
+
+        /*
+         * elevator indicated where it wants this request to be
+         * inserted at elevator_merge time
+         */
+        __elv_add_request(q, req, ELEVATOR_INSERT_SORT, 0);
+}
+ 
+/*
+ * disk_round_stats()   - Round off the performance stats on a struct
+ * disk_stats.
+ *
+ * The average IO queue length and utilisation statistics are maintained
+ * by observing the current state of the queue length and the amount of
+ * time it has been in this state for.
+ *
+ * Normally, that accounting is done on IO completion, but that can result
+ * in more than a second's worth of IO being accounted for within any one
+ * second, leading to >100% utilisation.  To deal with that, we call this
+ * function to do a round-off before returning the results when reading
+ * /proc/diskstats.  This accounts immediately for all queue usage up to
+ * the current jiffies and restarts the counters again.
+ */
+void disk_round_stats(struct gendisk *disk)
+{
+        unsigned long now = jiffies;
+
+        if (now == disk->stamp)
+                return;
+
+        if (disk->in_flight) {
+                __disk_stat_add(disk, time_in_queue,
+                                disk->in_flight * (now - disk->stamp));
+                __disk_stat_add(disk, io_ticks, (now - disk->stamp));
+        }
+        disk->stamp = now;
+}
+
+EXPORT_SYMBOL_GPL(disk_round_stats);
+
+/*
+ * queue lock must be held
+ */
+void __blk_put_request(struct request_queue *q, struct request *req)
+{
+        if (unlikely(!q))
+                return;
+        if (unlikely(--req->ref_count))
+                return;
+
+        elv_completed_request(q, req);
+
+        /*
+         * Request may not have originated from ll_rw_blk. if not,
+         * it didn't come out of our reserved rq pools
+         */
+        if (req->cmd_flags & REQ_ALLOCED) {
+                int rw = rq_data_dir(req);
+                int priv = req->cmd_flags & REQ_ELVPRIV;
+
+                BUG_ON(!list_empty(&req->queuelist));
+                BUG_ON(!hlist_unhashed(&req->hash));
+
+                blk_free_request(q, req);
+                freed_request(q, rw, priv);
+        }
+}
+
+EXPORT_SYMBOL_GPL(__blk_put_request);
+
+void blk_put_request(struct request *req)
+{
+        unsigned long flags;
+        struct request_queue *q = req->q;
+
+        /*
+         * Gee, IDE calls in w/ NULL q.  Fix IDE and remove the
+         * following if (q) test.
+         */
+        if (q) {
+                spin_lock_irqsave(q->queue_lock, flags);
+                __blk_put_request(q, req);
+                spin_unlock_irqrestore(q->queue_lock, flags);
+        }
+}
+
+EXPORT_SYMBOL(blk_put_request);
+
+/**
+ * blk_end_sync_rq - executes a completion event on a request
+ * @rq: request to complete
+ * @error: end io status of the request
+ */
+void blk_end_sync_rq(struct request *rq, int error)
+{
+        struct completion *waiting = rq->end_io_data;
+
+        rq->end_io_data = NULL;
+        __blk_put_request(rq->q, rq);
+
+        /*
+         * complete last, if this is a stack request the process (and thus
+         * the rq pointer) could be invalid right after this complete()
+         */
+        complete(waiting);
+}
+EXPORT_SYMBOL(blk_end_sync_rq);
+
+/*
+ * Has to be called with the request spinlock acquired
+ */
+static int attempt_merge(struct request_queue *q, struct request *req,
+                          struct request *next)
+{
+        if (!rq_mergeable(req) || !rq_mergeable(next))
+                return 0;
+
+        /*
+         * not contiguous
+         */
+        if (req->sector + req->nr_sectors != next->sector)
+                return 0;
+
+        if (rq_data_dir(req) != rq_data_dir(next)
+            || req->rq_disk != next->rq_disk
+            || next->special)
+                return 0;
+
+        /*
+         * If we are allowed to merge, then append bio list
+         * from next to rq and release next. merge_requests_fn
+         * will have updated segment counts, update sector
+         * counts here.
+         */
+        if (!ll_merge_requests_fn(q, req, next))
+                return 0;
+
+        /*
+         * At this point we have either done a back merge
+         * or front merge. We need the smaller start_time of
+         * the merged requests to be the current request
+         * for accounting purposes.
+         */
+        if (time_after(req->start_time, next->start_time))
+                req->start_time = next->start_time;
+
+        req->biotail->bi_next = next->bio;
+        req->biotail = next->biotail;
+
+        req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
+
+        elv_merge_requests(q, req, next);
+
+        if (req->rq_disk) {
+                disk_round_stats(req->rq_disk);
+                req->rq_disk->in_flight--;
+        }
+
+        req->ioprio = ioprio_best(req->ioprio, next->ioprio);
+
+        __blk_put_request(q, next);
+        return 1;
+}
+
+static inline int attempt_back_merge(struct request_queue *q,
+                                     struct request *rq)
+{
+        struct request *next = elv_latter_request(q, rq);
+
+        if (next)
+                return attempt_merge(q, rq, next);
+
+        return 0;
+}
+
+static inline int attempt_front_merge(struct request_queue *q,
+                                      struct request *rq)
+{
+        struct request *prev = elv_former_request(q, rq);
+
+        if (prev)
+                return attempt_merge(q, prev, rq);
+
+        return 0;
+}
+
+static void init_request_from_bio(struct request *req, struct bio *bio)
+{
+        req->cmd_type = REQ_TYPE_FS;
+
+        /*
+         * inherit FAILFAST from bio (for read-ahead, and explicit FAILFAST)
+         */
+        if (bio_rw_ahead(bio) || bio_failfast(bio))
+                req->cmd_flags |= REQ_FAILFAST;
+
+        /*
+         * REQ_BARRIER implies no merging, but lets make it explicit
+         */
+        if (unlikely(bio_barrier(bio)))
+                req->cmd_flags |= (REQ_HARDBARRIER | REQ_NOMERGE);
+
+        if (bio_sync(bio))
+                req->cmd_flags |= REQ_RW_SYNC;
+        if (bio_rw_meta(bio))
+                req->cmd_flags |= REQ_RW_META;
+
+        req->errors = 0;
+        req->hard_sector = req->sector = bio->bi_sector;
+        req->ioprio = bio_prio(bio);
+        req->start_time = jiffies;
+        blk_rq_bio_prep(req->q, req, bio);
+}
+
+static int __make_request(struct request_queue *q, struct bio *bio)
+{
+        struct request *req;
+        int el_ret, nr_sectors, barrier, err;
+        const unsigned short prio = bio_prio(bio);
+        const int sync = bio_sync(bio);
+        int rw_flags;
+
+        nr_sectors = bio_sectors(bio);
+
+        /*
+         * low level driver can indicate that it wants pages above a
+         * certain limit bounced to low memory (ie for highmem, or even
+         * ISA dma in theory)
+         */
+        blk_queue_bounce(q, &bio);
+
+        barrier = bio_barrier(bio);
+        if (unlikely(barrier) && (q->next_ordered == QUEUE_ORDERED_NONE)) {
+                err = -EOPNOTSUPP;
+                goto end_io;
+        }
+
+        spin_lock_irq(q->queue_lock);
+
+        if (unlikely(barrier) || elv_queue_empty(q))
+                goto get_rq;
+
+        el_ret = elv_merge(q, &req, bio);
+        switch (el_ret) {
+                case ELEVATOR_BACK_MERGE:
+                        BUG_ON(!rq_mergeable(req));
+
+                        if (!ll_back_merge_fn(q, req, bio))
+                                break;
+
+                        blk_add_trace_bio(q, bio, BLK_TA_BACKMERGE);
+
+                        req->biotail->bi_next = bio;
+                        req->biotail = bio;
+                        req->nr_sectors = req->hard_nr_sectors += nr_sectors;
+                        req->ioprio = ioprio_best(req->ioprio, prio);
+                        drive_stat_acct(req, 0);
+                        if (!attempt_back_merge(q, req))
+                                elv_merged_request(q, req, el_ret);
+                        goto out;
+
+                case ELEVATOR_FRONT_MERGE:
+                        BUG_ON(!rq_mergeable(req));
+
+                        if (!ll_front_merge_fn(q, req, bio))
+                                break;
+
+                        blk_add_trace_bio(q, bio, BLK_TA_FRONTMERGE);
+
+                        bio->bi_next = req->bio;
+                        req->bio = bio;
+
+                        /*
+                         * may not be valid. if the low level driver said
+                         * it didn't need a bounce buffer then it better
+                         * not touch req->buffer either...
+                         */
+                        req->buffer = bio_data(bio);
+                        req->current_nr_sectors = bio_cur_sectors(bio);
+                        req->hard_cur_sectors = req->current_nr_sectors;
+                        req->sector = req->hard_sector = bio->bi_sector;
+                        req->nr_sectors = req->hard_nr_sectors += nr_sectors;
+                        req->ioprio = ioprio_best(req->ioprio, prio);
+                        drive_stat_acct(req, 0);
+                        if (!attempt_front_merge(q, req))
+                                elv_merged_request(q, req, el_ret);
+                        goto out;
+
+                /* ELV_NO_MERGE: elevator says don't/can't merge. */
+                default:
+                        ;
+        }
+
+get_rq:
+        /*
+         * This sync check and mask will be re-done in init_request_from_bio(),
+         * but we need to set it earlier to expose the sync flag to the
+         * rq allocator and io schedulers.
+         */
+        rw_flags = bio_data_dir(bio);
+        if (sync)
+                rw_flags |= REQ_RW_SYNC;
+
+        /*
+         * Grab a free request. This is might sleep but can not fail.
+         * Returns with the queue unlocked.
+         */
+        req = get_request_wait(q, rw_flags, bio);
+
+        /*
+         * After dropping the lock and possibly sleeping here, our request
+         * may now be mergeable after it had proven unmergeable (above).
+         * We don't worry about that case for efficiency. It won't happen
+         * often, and the elevators are able to handle it.
+         */
+        init_request_from_bio(req, bio);
+
+        spin_lock_irq(q->queue_lock);
+        if (elv_queue_empty(q))
+                blk_plug_device(q);
+        add_request(q, req);
+out:
+        if (sync)
+                __generic_unplug_device(q);
+
+        spin_unlock_irq(q->queue_lock);
+        return 0;
+
+end_io:
+        bio_endio(bio, err);
+        return 0;
+}
+
+/*
+ * If bio->bi_dev is a partition, remap the location
+ */
+static inline void blk_partition_remap(struct bio *bio)
+{
+        struct block_device *bdev = bio->bi_bdev;
+
+        if (bio_sectors(bio) && bdev != bdev->bd_contains) {
+                struct hd_struct *p = bdev->bd_part;
+                const int rw = bio_data_dir(bio);
+
+                p->sectors[rw] += bio_sectors(bio);
+                p->ios[rw]++;
+
+                bio->bi_sector += p->start_sect;
+                bio->bi_bdev = bdev->bd_contains;
+
+                blk_add_trace_remap(bdev_get_queue(bio->bi_bdev), bio,
+                                    bdev->bd_dev, bio->bi_sector,
+                                    bio->bi_sector - p->start_sect);
+        }
+}
+
+static void handle_bad_sector(struct bio *bio)
+{
+        char b[BDEVNAME_SIZE];
+
+        printk(KERN_INFO "attempt to access beyond end of device\n");
+        printk(KERN_INFO "%s: rw=%ld, want=%Lu, limit=%Lu\n",
+                        bdevname(bio->bi_bdev, b),
+                        bio->bi_rw,
+                        (unsigned long long)bio->bi_sector + bio_sectors(bio),
+                        (long long)(bio->bi_bdev->bd_inode->i_size >> 9));
+
+        set_bit(BIO_EOF, &bio->bi_flags);
+}
+
+#ifdef CONFIG_FAIL_MAKE_REQUEST
+
+static DECLARE_FAULT_ATTR(fail_make_request);
+
+static int __init setup_fail_make_request(char *str)
+{
+        return setup_fault_attr(&fail_make_request, str);
+}
+__setup("fail_make_request=", setup_fail_make_request);
+
+static int should_fail_request(struct bio *bio)
+{
+        if ((bio->bi_bdev->bd_disk->flags & GENHD_FL_FAIL) ||
+            (bio->bi_bdev->bd_part && bio->bi_bdev->bd_part->make_it_fail))
+                return should_fail(&fail_make_request, bio->bi_size);
+
+        return 0;
+}
+
+static int __init fail_make_request_debugfs(void)
+{
+        return init_fault_attr_dentries(&fail_make_request,
+                                        "fail_make_request");
+}
+
+late_initcall(fail_make_request_debugfs);
+
+#else /* CONFIG_FAIL_MAKE_REQUEST */
+
+static inline int should_fail_request(struct bio *bio)
+{
+        return 0;
+}
+
+#endif /* CONFIG_FAIL_MAKE_REQUEST */
+
+/*
+ * Check whether this bio extends beyond the end of the device.
+ */
+static inline int bio_check_eod(struct bio *bio, unsigned int nr_sectors)
+{
+        sector_t maxsector;
+
+        if (!nr_sectors)
+                return 0;
+
+        /* Test device or partition size, when known. */
+        maxsector = bio->bi_bdev->bd_inode->i_size >> 9;
+        if (maxsector) {
+                sector_t sector = bio->bi_sector;
+
+                if (maxsector < nr_sectors || maxsector - nr_sectors < sector) {
+                        /*
+                         * This may well happen - the kernel calls bread()
+                         * without checking the size of the device, e.g., when
+                         * mounting a device.
+                         */
+                        handle_bad_sector(bio);
+                        return 1;
+                }
+        }
+
+        return 0;
+}
+
+/**
+ * generic_make_request: hand a buffer to its device driver for I/O
+ * @bio:  The bio describing the location in memory and on the device.
+ *
+ * generic_make_request() is used to make I/O requests of block
+ * devices. It is passed a &struct bio, which describes the I/O that needs
+ * to be done.
+ *
+ * generic_make_request() does not return any status.  The
+ * success/failure status of the request, along with notification of
+ * completion, is delivered asynchronously through the bio->bi_end_io
+ * function described (one day) else where.
+ *
+ * The caller of generic_make_request must make sure that bi_io_vec
+ * are set to describe the memory buffer, and that bi_dev and bi_sector are
+ * set to describe the device address, and the
+ * bi_end_io and optionally bi_private are set to describe how
+ * completion notification should be signaled.
+ *
+ * generic_make_request and the drivers it calls may use bi_next if this
+ * bio happens to be merged with someone else, and may change bi_dev and
+ * bi_sector for remaps as it sees fit.  So the values of these fields
+ * should NOT be depended on after the call to generic_make_request.
+ */
+static inline void __generic_make_request(struct bio *bio)
+{
+        struct request_queue *q;
+        sector_t old_sector;
+        int ret, nr_sectors = bio_sectors(bio);
+        dev_t old_dev;
+        int err = -EIO;
+
+        might_sleep();
+
+        if (bio_check_eod(bio, nr_sectors))
+                goto end_io;
+
+        /*
+         * Resolve the mapping until finished. (drivers are
+         * still free to implement/resolve their own stacking
+         * by explicitly returning 0)
+         *
+         * NOTE: we don't repeat the blk_size check for each new device.
+         * Stacking drivers are expected to know what they are doing.
+         */
+        old_sector = -1;
+        old_dev = 0;
+        do {
+                char b[BDEVNAME_SIZE];
+
+                q = bdev_get_queue(bio->bi_bdev);
+                if (!q) {
+                        printk(KERN_ERR
+                               "generic_make_request: Trying to access "
+                                "nonexistent block-device %s (%Lu)\n",
+                                bdevname(bio->bi_bdev, b),
+                                (long long) bio->bi_sector);
+end_io:
+                        bio_endio(bio, err);
+                        break;
+                }
+
+                if (unlikely(nr_sectors > q->max_hw_sectors)) {
+                        printk("bio too big device %s (%u > %u)\n", 
+                                bdevname(bio->bi_bdev, b),
+                                bio_sectors(bio),
+                                q->max_hw_sectors);
+                        goto end_io;
+                }
+
+                if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
+                        goto end_io;
+
+                if (should_fail_request(bio))
+                        goto end_io;
+
+                /*
+                 * If this device has partitions, remap block n
+                 * of partition p to block n+start(p) of the disk.
+                 */
+                blk_partition_remap(bio);
+
+                if (old_sector != -1)
+                        blk_add_trace_remap(q, bio, old_dev, bio->bi_sector,
+                                            old_sector);
+
+                blk_add_trace_bio(q, bio, BLK_TA_QUEUE);
+
+                old_sector = bio->bi_sector;
+                old_dev = bio->bi_bdev->bd_dev;
+
+                if (bio_check_eod(bio, nr_sectors))
+                        goto end_io;
+                if (bio_empty_barrier(bio) && !q->prepare_flush_fn) {
+                        err = -EOPNOTSUPP;
+                        goto end_io;
+                }
+
+                ret = q->make_request_fn(q, bio);
+        } while (ret);
+}
+
+/*
+ * We only want one ->make_request_fn to be active at a time,
+ * else stack usage with stacked devices could be a problem.
+ * So use current->bio_{list,tail} to keep a list of requests
+ * submited by a make_request_fn function.
+ * current->bio_tail is also used as a flag to say if
+ * generic_make_request is currently active in this task or not.
+ * If it is NULL, then no make_request is active.  If it is non-NULL,
+ * then a make_request is active, and new requests should be added
+ * at the tail
+ */
+void generic_make_request(struct bio *bio)
+{
+        if (current->bio_tail) {
+                /* make_request is active */
+                *(current->bio_tail) = bio;
+                bio->bi_next = NULL;
+                current->bio_tail = &bio->bi_next;
+                return;
+        }
+        /* following loop may be a bit non-obvious, and so deserves some
+         * explanation.
+         * Before entering the loop, bio->bi_next is NULL (as all callers
+         * ensure that) so we have a list with a single bio.
+         * We pretend that we have just taken it off a longer list, so
+         * we assign bio_list to the next (which is NULL) and bio_tail
+         * to &bio_list, thus initialising the bio_list of new bios to be
+         * added.  __generic_make_request may indeed add some more bios
+         * through a recursive call to generic_make_request.  If it
+         * did, we find a non-NULL value in bio_list and re-enter the loop
+         * from the top.  In this case we really did just take the bio
+         * of the top of the list (no pretending) and so fixup bio_list and
+         * bio_tail or bi_next, and call into __generic_make_request again.
+         *
+         * The loop was structured like this to make only one call to
+         * __generic_make_request (which is important as it is large and
+         * inlined) and to keep the structure simple.
+         */
+        BUG_ON(bio->bi_next);
+        do {
+                current->bio_list = bio->bi_next;
+                if (bio->bi_next == NULL)
+                        current->bio_tail = &current->bio_list;
+                else
+                        bio->bi_next = NULL;
+                __generic_make_request(bio);
+                bio = current->bio_list;
+        } while (bio);
+        current->bio_tail = NULL; /* deactivate */
+}
+
+EXPORT_SYMBOL(generic_make_request);
+
+/**
+ * submit_bio: submit a bio to the block device layer for I/O
+ * @rw: whether to %READ or %WRITE, or maybe to %READA (read ahead)
+ * @bio: The &struct bio which describes the I/O
+ *
+ * submit_bio() is very similar in purpose to generic_make_request(), and
+ * uses that function to do most of the work. Both are fairly rough
+ * interfaces, @bio must be presetup and ready for I/O.
+ *
+ */
+void submit_bio(int rw, struct bio *bio)
+{
+        int count = bio_sectors(bio);
+
+        bio->bi_rw |= rw;
+
+        /*
+         * If it's a regular read/write or a barrier with data attached,
+         * go through the normal accounting stuff before submission.
+         */
+        if (!bio_empty_barrier(bio)) {
+
+                BIO_BUG_ON(!bio->bi_size);
+                BIO_BUG_ON(!bio->bi_io_vec);
+
+                if (rw & WRITE) {
+                        count_vm_events(PGPGOUT, count);
+                } else {
+                        task_io_account_read(bio->bi_size);
+                        count_vm_events(PGPGIN, count);
+                }
+
+                if (unlikely(block_dump)) {
+                        char b[BDEVNAME_SIZE];
+                        printk(KERN_DEBUG "%s(%d): %s block %Lu on %s\n",
+                        current->comm, task_pid_nr(current),
+                                (rw & WRITE) ? "WRITE" : "READ",
+                                (unsigned long long)bio->bi_sector,
+                                bdevname(bio->bi_bdev,b));
+                }
+        }
+
+        generic_make_request(bio);
+}
+
+EXPORT_SYMBOL(submit_bio);
+
+static void blk_recalc_rq_sectors(struct request *rq, int nsect)
+{
+        if (blk_fs_request(rq)) {
+                rq->hard_sector += nsect;
+                rq->hard_nr_sectors -= nsect;
+
+                /*
+                 * Move the I/O submission pointers ahead if required.
+                 */
+                if ((rq->nr_sectors >= rq->hard_nr_sectors) &&
+                    (rq->sector <= rq->hard_sector)) {
+                        rq->sector = rq->hard_sector;
+                        rq->nr_sectors = rq->hard_nr_sectors;
+                        rq->hard_cur_sectors = bio_cur_sectors(rq->bio);
+                        rq->current_nr_sectors = rq->hard_cur_sectors;
+                        rq->buffer = bio_data(rq->bio);
+                }
+
+                /*
+                 * if total number of sectors is less than the first segment
+                 * size, something has gone terribly wrong
+                 */
+                if (rq->nr_sectors < rq->current_nr_sectors) {
+                        printk("blk: request botched\n");
+                        rq->nr_sectors = rq->current_nr_sectors;
+                }
+        }
+}
+
+/**
+ * __end_that_request_first - end I/O on a request
+ * @req:      the request being processed
+ * @error:    0 for success, < 0 for error
+ * @nr_bytes: number of bytes to complete
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @req, and sets it up
+ *     for the next range of segments (if any) in the cluster.
+ *
+ * Return:
+ *     0 - we are done with this request, call end_that_request_last()
+ *     1 - still buffers pending for this request
+ **/
+static int __end_that_request_first(struct request *req, int error,
+                                    int nr_bytes)
+{
+        int total_bytes, bio_nbytes, next_idx = 0;
+        struct bio *bio;
+
+        blk_add_trace_rq(req->q, req, BLK_TA_COMPLETE);
+
+        /*
+         * for a REQ_BLOCK_PC request, we want to carry any eventual
+         * sense key with us all the way through
+         */
+        if (!blk_pc_request(req))
+                req->errors = 0;
+
+        if (error) {
+                if (blk_fs_request(req) && !(req->cmd_flags & REQ_QUIET))
+                        printk("end_request: I/O error, dev %s, sector %llu\n",
+                                req->rq_disk ? req->rq_disk->disk_name : "?",
+                                (unsigned long long)req->sector);
+        }
+
+        if (blk_fs_request(req) && req->rq_disk) {
+                const int rw = rq_data_dir(req);
+
+                disk_stat_add(req->rq_disk, sectors[rw], nr_bytes >> 9);
+        }
+
+        total_bytes = bio_nbytes = 0;
+        while ((bio = req->bio) != NULL) {
+                int nbytes;
+
+                /*
+                 * For an empty barrier request, the low level driver must
+                 * store a potential error location in ->sector. We pass
+                 * that back up in ->bi_sector.
+                 */
+                if (blk_empty_barrier(req))
+                        bio->bi_sector = req->sector;
+
+                if (nr_bytes >= bio->bi_size) {
+                        req->bio = bio->bi_next;
+                        nbytes = bio->bi_size;
+                        req_bio_endio(req, bio, nbytes, error);
+                        next_idx = 0;
+                        bio_nbytes = 0;
+                } else {
+                        int idx = bio->bi_idx + next_idx;
+
+                        if (unlikely(bio->bi_idx >= bio->bi_vcnt)) {
+                                blk_dump_rq_flags(req, "__end_that");
+                                printk("%s: bio idx %d >= vcnt %d\n",
+                                                __FUNCTION__,
+                                                bio->bi_idx, bio->bi_vcnt);
+                                break;
+                        }
+
+                        nbytes = bio_iovec_idx(bio, idx)->bv_len;
+                        BIO_BUG_ON(nbytes > bio->bi_size);
+
+                        /*
+                         * not a complete bvec done
+                         */
+                        if (unlikely(nbytes > nr_bytes)) {
+                                bio_nbytes += nr_bytes;
+                                total_bytes += nr_bytes;
+                                break;
+                        }
+
+                        /*
+                         * advance to the next vector
+                         */
+                        next_idx++;
+                        bio_nbytes += nbytes;
+                }
+
+                total_bytes += nbytes;
+                nr_bytes -= nbytes;
+
+                if ((bio = req->bio)) {
+                        /*
+                         * end more in this run, or just return 'not-done'
+                         */
+                        if (unlikely(nr_bytes <= 0))
+                                break;
+                }
+        }
+
+        /*
+         * completely done
+         */
+        if (!req->bio)
+                return 0;
+
+        /*
+         * if the request wasn't completed, update state
+         */
+        if (bio_nbytes) {
+                req_bio_endio(req, bio, bio_nbytes, error);
+                bio->bi_idx += next_idx;
+                bio_iovec(bio)->bv_offset += nr_bytes;
+                bio_iovec(bio)->bv_len -= nr_bytes;
+        }
+
+        blk_recalc_rq_sectors(req, total_bytes >> 9);
+        blk_recalc_rq_segments(req);
+        return 1;
+}
+
+/*
+ * splice the completion data to a local structure and hand off to
+ * process_completion_queue() to complete the requests
+ */
+static void blk_done_softirq(struct softirq_action *h)
+{
+        struct list_head *cpu_list, local_list;
+
+        local_irq_disable();
+        cpu_list = &__get_cpu_var(blk_cpu_done);
+        list_replace_init(cpu_list, &local_list);
+        local_irq_enable();
+
+        while (!list_empty(&local_list)) {
+                struct request *rq = list_entry(local_list.next, struct request, donelist);
+
+                list_del_init(&rq->donelist);
+                rq->q->softirq_done_fn(rq);
+        }
+}
+
+static int __cpuinit blk_cpu_notify(struct notifier_block *self, unsigned long action,
+                          void *hcpu)
+{
+        /*
+         * If a CPU goes away, splice its entries to the current CPU
+         * and trigger a run of the softirq
+         */
+        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
+                int cpu = (unsigned long) hcpu;
+
+                local_irq_disable();
+                list_splice_init(&per_cpu(blk_cpu_done, cpu),
+                                 &__get_cpu_var(blk_cpu_done));
+                raise_softirq_irqoff(BLOCK_SOFTIRQ);
+                local_irq_enable();
+        }
+
+        return NOTIFY_OK;
+}
+
+
+static struct notifier_block blk_cpu_notifier __cpuinitdata = {
+        .notifier_call  = blk_cpu_notify,
+};
+
+/**
+ * blk_complete_request - end I/O on a request
+ * @req:      the request being processed
+ *
+ * Description:
+ *     Ends all I/O on a request. It does not handle partial completions,
+ *     unless the driver actually implements this in its completion callback
+ *     through requeueing. The actual completion happens out-of-order,
+ *     through a softirq handler. The user must have registered a completion
+ *     callback through blk_queue_softirq_done().
+ **/
+
+void blk_complete_request(struct request *req)
+{
+        struct list_head *cpu_list;
+        unsigned long flags;
+
+        BUG_ON(!req->q->softirq_done_fn);
+                
+        local_irq_save(flags);
+
+        cpu_list = &__get_cpu_var(blk_cpu_done);
+        list_add_tail(&req->donelist, cpu_list);
+        raise_softirq_irqoff(BLOCK_SOFTIRQ);
+
+        local_irq_restore(flags);
+}
+
+EXPORT_SYMBOL(blk_complete_request);
+        
+/*
+ * queue lock must be held
+ */
+static void end_that_request_last(struct request *req, int error)
+{
+        struct gendisk *disk = req->rq_disk;
+
+        if (blk_rq_tagged(req))
+                blk_queue_end_tag(req->q, req);
+
+        if (blk_queued_rq(req))
+                blkdev_dequeue_request(req);
+
+        if (unlikely(laptop_mode) && blk_fs_request(req))
+                laptop_io_completion();
+
+        /*
+         * Account IO completion.  bar_rq isn't accounted as a normal
+         * IO on queueing nor completion.  Accounting the containing
+         * request is enough.
+         */
+        if (disk && blk_fs_request(req) && req != &req->q->bar_rq) {
+                unsigned long duration = jiffies - req->start_time;
+                const int rw = rq_data_dir(req);
+
+                __disk_stat_inc(disk, ios[rw]);
+                __disk_stat_add(disk, ticks[rw], duration);
+                disk_round_stats(disk);
+                disk->in_flight--;
+        }
+
+        if (req->end_io)
+                req->end_io(req, error);
+        else {
+                if (blk_bidi_rq(req))
+                        __blk_put_request(req->next_rq->q, req->next_rq);
+
+                __blk_put_request(req->q, req);
+        }
+}
+
+static inline void __end_request(struct request *rq, int uptodate,
+                                 unsigned int nr_bytes)
+{
+        int error = 0;
+
+        if (uptodate <= 0)
+                error = uptodate ? uptodate : -EIO;
+
+        __blk_end_request(rq, error, nr_bytes);
+}
+
+/**
+ * blk_rq_bytes - Returns bytes left to complete in the entire request
+ **/
+unsigned int blk_rq_bytes(struct request *rq)
+{
+        if (blk_fs_request(rq))
+                return rq->hard_nr_sectors << 9;
+
+        return rq->data_len;
+}
+EXPORT_SYMBOL_GPL(blk_rq_bytes);
+
+/**
+ * blk_rq_cur_bytes - Returns bytes left to complete in the current segment
+ **/
+unsigned int blk_rq_cur_bytes(struct request *rq)
+{
+        if (blk_fs_request(rq))
+                return rq->current_nr_sectors << 9;
+
+        if (rq->bio)
+                return rq->bio->bi_size;
+
+        return rq->data_len;
+}
+EXPORT_SYMBOL_GPL(blk_rq_cur_bytes);
+
+/**
+ * end_queued_request - end all I/O on a queued request
+ * @rq:         the request being processed
+ * @uptodate:   error value or 0/1 uptodate flag
+ *
+ * Description:
+ *     Ends all I/O on a request, and removes it from the block layer queues.
+ *     Not suitable for normal IO completion, unless the driver still has
+ *     the request attached to the block layer.
+ *
+ **/
+void end_queued_request(struct request *rq, int uptodate)
+{
+        __end_request(rq, uptodate, blk_rq_bytes(rq));
+}
+EXPORT_SYMBOL(end_queued_request);
+
+/**
+ * end_dequeued_request - end all I/O on a dequeued request
+ * @rq:         the request being processed
+ * @uptodate:   error value or 0/1 uptodate flag
+ *
+ * Description:
+ *     Ends all I/O on a request. The request must already have been
+ *     dequeued using blkdev_dequeue_request(), as is normally the case
+ *     for most drivers.
+ *
+ **/
+void end_dequeued_request(struct request *rq, int uptodate)
+{
+        __end_request(rq, uptodate, blk_rq_bytes(rq));
+}
+EXPORT_SYMBOL(end_dequeued_request);
+
+
+/**
+ * end_request - end I/O on the current segment of the request
+ * @req:        the request being processed
+ * @uptodate:   error value or 0/1 uptodate flag
+ *
+ * Description:
+ *     Ends I/O on the current segment of a request. If that is the only
+ *     remaining segment, the request is also completed and freed.
+ *
+ *     This is a remnant of how older block drivers handled IO completions.
+ *     Modern drivers typically end IO on the full request in one go, unless
+ *     they have a residual value to account for. For that case this function
+ *     isn't really useful, unless the residual just happens to be the
+ *     full current segment. In other words, don't use this function in new
+ *     code. Either use end_request_completely(), or the
+ *     end_that_request_chunk() (along with end_that_request_last()) for
+ *     partial completions.
+ *
+ **/
+void end_request(struct request *req, int uptodate)
+{
+        __end_request(req, uptodate, req->hard_cur_sectors << 9);
+}
+EXPORT_SYMBOL(end_request);
+
+/**
+ * blk_end_io - Generic end_io function to complete a request.
+ * @rq:           the request being processed
+ * @error:        0 for success, < 0 for error
+ * @nr_bytes:     number of bytes to complete @rq
+ * @bidi_bytes:   number of bytes to complete @rq->next_rq
+ * @drv_callback: function called between completion of bios in the request
+ *                and completion of the request.
+ *                If the callback returns non 0, this helper returns without
+ *                completion of the request.
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @rq and @rq->next_rq.
+ *     If @rq has leftover, sets it up for the next range of segments.
+ *
+ * Return:
+ *     0 - we are done with this request
+ *     1 - this request is not freed yet, it still has pending buffers.
+ **/
+static int blk_end_io(struct request *rq, int error, int nr_bytes,
+                      int bidi_bytes, int (drv_callback)(struct request *))
+{
+        struct request_queue *q = rq->q;
+        unsigned long flags = 0UL;
+
+        if (blk_fs_request(rq) || blk_pc_request(rq)) {
+                if (__end_that_request_first(rq, error, nr_bytes))
+                        return 1;
+
+                /* Bidi request must be completed as a whole */
+                if (blk_bidi_rq(rq) &&
+                    __end_that_request_first(rq->next_rq, error, bidi_bytes))
+                        return 1;
+        }
+
+        /* Special feature for tricky drivers */
+        if (drv_callback && drv_callback(rq))
+                return 1;
+
+        add_disk_randomness(rq->rq_disk);
+
+        spin_lock_irqsave(q->queue_lock, flags);
+        end_that_request_last(rq, error);
+        spin_unlock_irqrestore(q->queue_lock, flags);
+
+        return 0;
+}
+
+/**
+ * blk_end_request - Helper function for drivers to complete the request.
+ * @rq:       the request being processed
+ * @error:    0 for success, < 0 for error
+ * @nr_bytes: number of bytes to complete
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @rq.
+ *     If @rq has leftover, sets it up for the next range of segments.
+ *
+ * Return:
+ *     0 - we are done with this request
+ *     1 - still buffers pending for this request
+ **/
+int blk_end_request(struct request *rq, int error, int nr_bytes)
+{
+        return blk_end_io(rq, error, nr_bytes, 0, NULL);
+}
+EXPORT_SYMBOL_GPL(blk_end_request);
+
+/**
+ * __blk_end_request - Helper function for drivers to complete the request.
+ * @rq:       the request being processed
+ * @error:    0 for success, < 0 for error
+ * @nr_bytes: number of bytes to complete
+ *
+ * Description:
+ *     Must be called with queue lock held unlike blk_end_request().
+ *
+ * Return:
+ *     0 - we are done with this request
+ *     1 - still buffers pending for this request
+ **/
+int __blk_end_request(struct request *rq, int error, int nr_bytes)
+{
+        if (blk_fs_request(rq) || blk_pc_request(rq)) {
+                if (__end_that_request_first(rq, error, nr_bytes))
+                        return 1;
+        }
+
+        add_disk_randomness(rq->rq_disk);
+
+        end_that_request_last(rq, error);
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(__blk_end_request);
+
+/**
+ * blk_end_bidi_request - Helper function for drivers to complete bidi request.
+ * @rq:         the bidi request being processed
+ * @error:      0 for success, < 0 for error
+ * @nr_bytes:   number of bytes to complete @rq
+ * @bidi_bytes: number of bytes to complete @rq->next_rq
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @rq and @rq->next_rq.
+ *
+ * Return:
+ *     0 - we are done with this request
+ *     1 - still buffers pending for this request
+ **/
+int blk_end_bidi_request(struct request *rq, int error, int nr_bytes,
+                         int bidi_bytes)
+{
+        return blk_end_io(rq, error, nr_bytes, bidi_bytes, NULL);
+}
+EXPORT_SYMBOL_GPL(blk_end_bidi_request);
+
+/**
+ * blk_end_request_callback - Special helper function for tricky drivers
+ * @rq:           the request being processed
+ * @error:        0 for success, < 0 for error
+ * @nr_bytes:     number of bytes to complete
+ * @drv_callback: function called between completion of bios in the request
+ *                and completion of the request.
+ *                If the callback returns non 0, this helper returns without
+ *                completion of the request.
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @rq.
+ *     If @rq has leftover, sets it up for the next range of segments.
+ *
+ *     This special helper function is used only for existing tricky drivers.
+ *     (e.g. cdrom_newpc_intr() of ide-cd)
+ *     This interface will be removed when such drivers are rewritten.
+ *     Don't use this interface in other places anymore.
+ *
+ * Return:
+ *     0 - we are done with this request
+ *     1 - this request is not freed yet.
+ *         this request still has pending buffers or
+ *         the driver doesn't want to finish this request yet.
+ **/
+int blk_end_request_callback(struct request *rq, int error, int nr_bytes,
+                             int (drv_callback)(struct request *))
+{
+        return blk_end_io(rq, error, nr_bytes, 0, drv_callback);
+}
+EXPORT_SYMBOL_GPL(blk_end_request_callback);
+
+static void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
+                            struct bio *bio)
+{
+        /* first two bits are identical in rq->cmd_flags and bio->bi_rw */
+        rq->cmd_flags |= (bio->bi_rw & 3);
+
+        rq->nr_phys_segments = bio_phys_segments(q, bio);
+        rq->nr_hw_segments = bio_hw_segments(q, bio);
+        rq->current_nr_sectors = bio_cur_sectors(bio);
+        rq->hard_cur_sectors = rq->current_nr_sectors;
+        rq->hard_nr_sectors = rq->nr_sectors = bio_sectors(bio);
+        rq->buffer = bio_data(bio);
+        rq->data_len = bio->bi_size;
+
+        rq->bio = rq->biotail = bio;
+
+        if (bio->bi_bdev)
+                rq->rq_disk = bio->bi_bdev->bd_disk;
+}
+
+int kblockd_schedule_work(struct work_struct *work)
+{
+        return queue_work(kblockd_workqueue, work);
+}
+
+EXPORT_SYMBOL(kblockd_schedule_work);
+
+void kblockd_flush_work(struct work_struct *work)
+{
+        cancel_work_sync(work);
+}
+EXPORT_SYMBOL(kblockd_flush_work);
+
+int __init blk_dev_init(void)
+{
+        int i;
+
+        kblockd_workqueue = create_workqueue("kblockd");
+        if (!kblockd_workqueue)
+                panic("Failed to create kblockd\n");
+
+        request_cachep = kmem_cache_create("blkdev_requests",
+                        sizeof(struct request), 0, SLAB_PANIC, NULL);
+
+        requestq_cachep = kmem_cache_create("blkdev_queue",
+                        sizeof(struct request_queue), 0, SLAB_PANIC, NULL);
+
+        iocontext_cachep = kmem_cache_create("blkdev_ioc",
+                        sizeof(struct io_context), 0, SLAB_PANIC, NULL);
+
+        for_each_possible_cpu(i)
+                INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
+
+        open_softirq(BLOCK_SOFTIRQ, blk_done_softirq, NULL);
+        register_hotcpu_notifier(&blk_cpu_notifier);
+
+        blk_max_low_pfn = max_low_pfn - 1;
+        blk_max_pfn = max_pfn - 1;
+
+        return 0;
+}
+
+static void cfq_dtor(struct io_context *ioc)
+{
+        struct cfq_io_context *cic[1];
+        int r;
+
+        /*
+         * We don't have a specific key to lookup with, so use the gang
+         * lookup to just retrieve the first item stored. The cfq exit
+         * function will iterate the full tree, so any member will do.
+         */
+        r = radix_tree_gang_lookup(&ioc->radix_root, (void **) cic, 0, 1);
+        if (r > 0)
+                cic[0]->dtor(ioc);
+}
+
+/*
+ * IO Context helper functions. put_io_context() returns 1 if there are no
+ * more users of this io context, 0 otherwise.
+ */
+int put_io_context(struct io_context *ioc)
+{
+        if (ioc == NULL)
+                return 1;
+
+        BUG_ON(atomic_read(&ioc->refcount) == 0);
+
+        if (atomic_dec_and_test(&ioc->refcount)) {
+                rcu_read_lock();
+                if (ioc->aic && ioc->aic->dtor)
+                        ioc->aic->dtor(ioc->aic);
+                rcu_read_unlock();
+                cfq_dtor(ioc);
+
+                kmem_cache_free(iocontext_cachep, ioc);
+                return 1;
+        }
+        return 0;
+}
+EXPORT_SYMBOL(put_io_context);
+
+static void cfq_exit(struct io_context *ioc)
+{
+        struct cfq_io_context *cic[1];
+        int r;
+
+        rcu_read_lock();
+        /*
+         * See comment for cfq_dtor()
+         */
+        r = radix_tree_gang_lookup(&ioc->radix_root, (void **) cic, 0, 1);
+        rcu_read_unlock();
+
+        if (r > 0)
+                cic[0]->exit(ioc);
+}
+
+/* Called by the exitting task */
+void exit_io_context(void)
+{
+        struct io_context *ioc;
+
+        task_lock(current);
+        ioc = current->io_context;
+        current->io_context = NULL;
+        task_unlock(current);
+
+        if (atomic_dec_and_test(&ioc->nr_tasks)) {
+                if (ioc->aic && ioc->aic->exit)
+                        ioc->aic->exit(ioc->aic);
+                cfq_exit(ioc);
+
+                put_io_context(ioc);
+        }
+}
+
+struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
+{
+        struct io_context *ret;
+
+        ret = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node);
+        if (ret) {
+                atomic_set(&ret->refcount, 1);
+                atomic_set(&ret->nr_tasks, 1);
+                spin_lock_init(&ret->lock);
+                ret->ioprio_changed = 0;
+                ret->ioprio = 0;
+                ret->last_waited = jiffies; /* doesn't matter... */
+                ret->nr_batch_requests = 0; /* because this is 0 */
+                ret->aic = NULL;
+                INIT_RADIX_TREE(&ret->radix_root, GFP_ATOMIC | __GFP_HIGH);
+                ret->ioc_data = NULL;
+        }
+
+        return ret;
+}
+
+/*
+ * If the current task has no IO context then create one and initialise it.
+ * Otherwise, return its existing IO context.
+ *
+ * This returned IO context doesn't have a specifically elevated refcount,
+ * but since the current task itself holds a reference, the context can be
+ * used in general code, so long as it stays within `current` context.
+ */
+static struct io_context *current_io_context(gfp_t gfp_flags, int node)
+{
+        struct task_struct *tsk = current;
+        struct io_context *ret;
+
+        ret = tsk->io_context;
+        if (likely(ret))
+                return ret;
+
+        ret = alloc_io_context(gfp_flags, node);
+        if (ret) {
+                /* make sure set_task_ioprio() sees the settings above */
+                smp_wmb();
+                tsk->io_context = ret;
+        }
+
+        return ret;
+}
+
+/*
+ * If the current task has no IO context then create one and initialise it.
+ * If it does have a context, take a ref on it.
+ *
+ * This is always called in the context of the task which submitted the I/O.
+ */
+struct io_context *get_io_context(gfp_t gfp_flags, int node)
+{
+        struct io_context *ret = NULL;
+
+        /*
+         * Check for unlikely race with exiting task. ioc ref count is
+         * zero when ioc is being detached.
+         */
+        do {
+                ret = current_io_context(gfp_flags, node);
+                if (unlikely(!ret))
+                        break;
+        } while (!atomic_inc_not_zero(&ret->refcount));
+
+        return ret;
+}
+EXPORT_SYMBOL(get_io_context);
+
+void copy_io_context(struct io_context **pdst, struct io_context **psrc)
+{
+        struct io_context *src = *psrc;
+        struct io_context *dst = *pdst;
+
+        if (src) {
+                BUG_ON(atomic_read(&src->refcount) == 0);
+                atomic_inc(&src->refcount);
+                put_io_context(dst);
+                *pdst = src;
+        }
+}
+EXPORT_SYMBOL(copy_io_context);
+
+void swap_io_context(struct io_context **ioc1, struct io_context **ioc2)
+{
+        struct io_context *temp;
+        temp = *ioc1;
+        *ioc1 = *ioc2;
+        *ioc2 = temp;
+}
+EXPORT_SYMBOL(swap_io_context);
+
+/*
+ * sysfs parts below
+ */
+struct queue_sysfs_entry {
+        struct attribute attr;
+        ssize_t (*show)(struct request_queue *, char *);
+        ssize_t (*store)(struct request_queue *, const char *, size_t);
+};
+
+static ssize_t
+queue_var_show(unsigned int var, char *page)
+{
+        return sprintf(page, "%d\n", var);
+}
+
+static ssize_t
+queue_var_store(unsigned long *var, const char *page, size_t count)
+{
+        char *p = (char *) page;
+
+        *var = simple_strtoul(p, &p, 10);
+        return count;
+}
+
+static ssize_t queue_requests_show(struct request_queue *q, char *page)
+{
+        return queue_var_show(q->nr_requests, (page));
+}
+
+static ssize_t
+queue_requests_store(struct request_queue *q, const char *page, size_t count)
+{
+        struct request_list *rl = &q->rq;
+        unsigned long nr;
+        int ret = queue_var_store(&nr, page, count);
+        if (nr < BLKDEV_MIN_RQ)
+                nr = BLKDEV_MIN_RQ;
+
+        spin_lock_irq(q->queue_lock);
+        q->nr_requests = nr;
+        blk_queue_congestion_threshold(q);
+
+        if (rl->count[READ] >= queue_congestion_on_threshold(q))
+                blk_set_queue_congested(q, READ);
+        else if (rl->count[READ] < queue_congestion_off_threshold(q))
+                blk_clear_queue_congested(q, READ);
+
+        if (rl->count[WRITE] >= queue_congestion_on_threshold(q))
+                blk_set_queue_congested(q, WRITE);
+        else if (rl->count[WRITE] < queue_congestion_off_threshold(q))
+                blk_clear_queue_congested(q, WRITE);
+
+        if (rl->count[READ] >= q->nr_requests) {
+                blk_set_queue_full(q, READ);
+        } else if (rl->count[READ]+1 <= q->nr_requests) {
+                blk_clear_queue_full(q, READ);
+                wake_up(&rl->wait[READ]);
+        }
+
+        if (rl->count[WRITE] >= q->nr_requests) {
+                blk_set_queue_full(q, WRITE);
+        } else if (rl->count[WRITE]+1 <= q->nr_requests) {
+                blk_clear_queue_full(q, WRITE);
+                wake_up(&rl->wait[WRITE]);
+        }
+        spin_unlock_irq(q->queue_lock);
+        return ret;
+}
+
+static ssize_t queue_ra_show(struct request_queue *q, char *page)
+{
+        int ra_kb = q->backing_dev_info.ra_pages << (PAGE_CACHE_SHIFT - 10);
+
+        return queue_var_show(ra_kb, (page));
+}
+
+static ssize_t
+queue_ra_store(struct request_queue *q, const char *page, size_t count)
+{
+        unsigned long ra_kb;
+        ssize_t ret = queue_var_store(&ra_kb, page, count);
+
+        spin_lock_irq(q->queue_lock);
+        q->backing_dev_info.ra_pages = ra_kb >> (PAGE_CACHE_SHIFT - 10);
+        spin_unlock_irq(q->queue_lock);
+
+        return ret;
+}
+
+static ssize_t queue_max_sectors_show(struct request_queue *q, char *page)
+{
+        int max_sectors_kb = q->max_sectors >> 1;
+
+        return queue_var_show(max_sectors_kb, (page));
+}
+
+static ssize_t
+queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
+{
+        unsigned long max_sectors_kb,
+                        max_hw_sectors_kb = q->max_hw_sectors >> 1,
+                        page_kb = 1 << (PAGE_CACHE_SHIFT - 10);
+        ssize_t ret = queue_var_store(&max_sectors_kb, page, count);
+
+        if (max_sectors_kb > max_hw_sectors_kb || max_sectors_kb < page_kb)
+                return -EINVAL;
+        /*
+         * Take the queue lock to update the readahead and max_sectors
+         * values synchronously:
+         */
+        spin_lock_irq(q->queue_lock);
+        q->max_sectors = max_sectors_kb << 1;
+        spin_unlock_irq(q->queue_lock);
+
+        return ret;
+}
+
+static ssize_t queue_max_hw_sectors_show(struct request_queue *q, char *page)
+{
+        int max_hw_sectors_kb = q->max_hw_sectors >> 1;
+
+        return queue_var_show(max_hw_sectors_kb, (page));
+}
+
+
+static struct queue_sysfs_entry queue_requests_entry = {
+        .attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
+        .show = queue_requests_show,
+        .store = queue_requests_store,
+};
+
+static struct queue_sysfs_entry queue_ra_entry = {
+        .attr = {.name = "read_ahead_kb", .mode = S_IRUGO | S_IWUSR },
+        .show = queue_ra_show,
+        .store = queue_ra_store,
+};
+
+static struct queue_sysfs_entry queue_max_sectors_entry = {
+        .attr = {.name = "max_sectors_kb", .mode = S_IRUGO | S_IWUSR },
+        .show = queue_max_sectors_show,
+        .store = queue_max_sectors_store,
+};
+
+static struct queue_sysfs_entry queue_max_hw_sectors_entry = {
+        .attr = {.name = "max_hw_sectors_kb", .mode = S_IRUGO },
+        .show = queue_max_hw_sectors_show,
+};
+
+static struct queue_sysfs_entry queue_iosched_entry = {
+        .attr = {.name = "scheduler", .mode = S_IRUGO | S_IWUSR },
+        .show = elv_iosched_show,
+        .store = elv_iosched_store,
+};
+
+static struct attribute *default_attrs[] = {
+        &queue_requests_entry.attr,
+        &queue_ra_entry.attr,
+        &queue_max_hw_sectors_entry.attr,
+        &queue_max_sectors_entry.attr,
+        &queue_iosched_entry.attr,
+        NULL,
+};
+
+#define to_queue(atr) container_of((atr), struct queue_sysfs_entry, attr)
+
+static ssize_t
+queue_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
+{
+        struct queue_sysfs_entry *entry = to_queue(attr);
+        struct request_queue *q =
+                container_of(kobj, struct request_queue, kobj);
+        ssize_t res;
+
+        if (!entry->show)
+                return -EIO;
+        mutex_lock(&q->sysfs_lock);
+        if (test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)) {
+                mutex_unlock(&q->sysfs_lock);
+                return -ENOENT;
+        }
+        res = entry->show(q, page);
+        mutex_unlock(&q->sysfs_lock);
+        return res;
+}
+
+static ssize_t
+queue_attr_store(struct kobject *kobj, struct attribute *attr,
+                    const char *page, size_t length)
+{
+        struct queue_sysfs_entry *entry = to_queue(attr);
+        struct request_queue *q = container_of(kobj, struct request_queue, kobj);
+
+        ssize_t res;
+
+        if (!entry->store)
+                return -EIO;
+        mutex_lock(&q->sysfs_lock);
+        if (test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)) {
+                mutex_unlock(&q->sysfs_lock);
+                return -ENOENT;
+        }
+        res = entry->store(q, page, length);
+        mutex_unlock(&q->sysfs_lock);
+        return res;
+}
+
+static struct sysfs_ops queue_sysfs_ops = {
+        .show   = queue_attr_show,
+        .store  = queue_attr_store,
+};
+
+static struct kobj_type queue_ktype = {
+        .sysfs_ops      = &queue_sysfs_ops,
+        .default_attrs  = default_attrs,
+        .release        = blk_release_queue,
+};
+
+int blk_register_queue(struct gendisk *disk)
+{
+        int ret;
+
+        struct request_queue *q = disk->queue;
+
+        if (!q || !q->request_fn)
+                return -ENXIO;
+
+        ret = kobject_add(&q->kobj, kobject_get(&disk->dev.kobj),
+                          "%s", "queue");
+        if (ret < 0)
+                return ret;
+
+        kobject_uevent(&q->kobj, KOBJ_ADD);
+
+        ret = elv_register_queue(q);
+        if (ret) {
+                kobject_uevent(&q->kobj, KOBJ_REMOVE);
+                kobject_del(&q->kobj);
+                return ret;
+        }
+
+        return 0;
+}
+
+void blk_unregister_queue(struct gendisk *disk)
+{
+        struct request_queue *q = disk->queue;
+
+        if (q && q->request_fn) {
+                elv_unregister_queue(q);
+
+                kobject_uevent(&q->kobj, KOBJ_REMOVE);
+                kobject_del(&q->kobj);
+                kobject_put(&disk->dev.kobj);
+        }
+}