[BLOCK] Move all core block layer code to new block/ directory

drivers/block/ is right now a mix of core and driver parts. Lets move
the core parts to a new top level directory. Al will move the fs/
related block parts to block/ next.

Signed-off-by: Jens Axboe <axboe@suse.de>

1 files changed, 3613 insertions, 0 deletions

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
new file mode 100644
index 000000000000..2747741677fb
--- /dev/null
+++ b/block/ll_rw_blk.c
@@ -0,0 +1,3613 @@
+/*
+ *  linux/drivers/block/ll_rw_blk.c
+ *
+ * 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/config.h>
+#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/blkdev.h>
+
+/*
+ * for max sense size
+ */
+#include <scsi/scsi_cmnd.h>
+
+static void blk_unplug_work(void *data);
+static void blk_unplug_timeout(unsigned long data);
+static void drive_stat_acct(struct request *rq, int nr_sectors, int new_io);
+
+/*
+ * For the allocated request tables
+ */
+static kmem_cache_t *request_cachep;
+
+/*
+ * For queue allocation
+ */
+static kmem_cache_t *requestq_cachep;
+
+/*
+ * For io context allocations
+ */
+static kmem_cache_t *iocontext_cachep;
+
+static wait_queue_head_t congestion_wqh[2] = {
+                __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
+                __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
+        };
+
+/*
+ * 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);
+
+/* 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;
+}
+
+/*
+ * A queue has just exitted congestion.  Note this in the global counter of
+ * congested queues, and wake up anyone who was waiting for requests to be
+ * put back.
+ */
+static void clear_queue_congested(request_queue_t *q, int rw)
+{
+        enum bdi_state bit;
+        wait_queue_head_t *wqh = &congestion_wqh[rw];
+
+        bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
+        clear_bit(bit, &q->backing_dev_info.state);
+        smp_mb__after_clear_bit();
+        if (waitqueue_active(wqh))
+                wake_up(wqh);
+}
+
+/*
+ * A queue has just entered congestion.  Flag that in the queue's VM-visible
+ * state flags and increment the global gounter of congested queues.
+ */
+static void set_queue_congested(request_queue_t *q, int rw)
+{
+        enum bdi_state bit;
+
+        bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
+        set_bit(bit, &q->backing_dev_info.state);
+}
+
+/**
+ * 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;
+        request_queue_t *q = bdev_get_queue(bdev);
+
+        if (q)
+                ret = &q->backing_dev_info;
+        return ret;
+}
+
+EXPORT_SYMBOL(blk_get_backing_dev_info);
+
+void blk_queue_activity_fn(request_queue_t *q, activity_fn *fn, void *data)
+{
+        q->activity_fn = fn;
+        q->activity_data = data;
+}
+
+EXPORT_SYMBOL(blk_queue_activity_fn);
+
+/**
+ * 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(request_queue_t *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(request_queue_t *q, merge_bvec_fn *mbfn)
+{
+        q->merge_bvec_fn = mbfn;
+}
+
+EXPORT_SYMBOL(blk_queue_merge_bvec);
+
+/**
+ * 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(request_queue_t * 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, 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);
+
+        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);
+
+        blk_queue_activity_fn(q, NULL, NULL);
+}
+
+EXPORT_SYMBOL(blk_queue_make_request);
+
+static inline void rq_init(request_queue_t *q, struct request *rq)
+{
+        INIT_LIST_HEAD(&rq->queuelist);
+
+        rq->errors = 0;
+        rq->rq_status = RQ_ACTIVE;
+        rq->bio = rq->biotail = NULL;
+        rq->ioprio = 0;
+        rq->buffer = NULL;
+        rq->ref_count = 1;
+        rq->q = q;
+        rq->waiting = NULL;
+        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;
+}
+
+/**
+ * blk_queue_ordered - does this queue support ordered writes
+ * @q:     the request queue
+ * @flag:  see below
+ *
+ * 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.
+ *
+ **/
+void blk_queue_ordered(request_queue_t *q, int flag)
+{
+        switch (flag) {
+                case QUEUE_ORDERED_NONE:
+                        if (q->flush_rq)
+                                kmem_cache_free(request_cachep, q->flush_rq);
+                        q->flush_rq = NULL;
+                        q->ordered = flag;
+                        break;
+                case QUEUE_ORDERED_TAG:
+                        q->ordered = flag;
+                        break;
+                case QUEUE_ORDERED_FLUSH:
+                        q->ordered = flag;
+                        if (!q->flush_rq)
+                                q->flush_rq = kmem_cache_alloc(request_cachep,
+                                                                GFP_KERNEL);
+                        break;
+                default:
+                        printk("blk_queue_ordered: bad value %d\n", flag);
+                        break;
+        }
+}
+
+EXPORT_SYMBOL(blk_queue_ordered);
+
+/**
+ * blk_queue_issue_flush_fn - set function for issuing a flush
+ * @q:     the request queue
+ * @iff:   the function to be called issuing the flush
+ *
+ * Description:
+ *   If a driver supports issuing a flush command, the support is notified
+ *   to the block layer by defining it through this call.
+ *
+ **/
+void blk_queue_issue_flush_fn(request_queue_t *q, issue_flush_fn *iff)
+{
+        q->issue_flush_fn = iff;
+}
+
+EXPORT_SYMBOL(blk_queue_issue_flush_fn);
+
+/*
+ * Cache flushing for ordered writes handling
+ */
+static void blk_pre_flush_end_io(struct request *flush_rq)
+{
+        struct request *rq = flush_rq->end_io_data;
+        request_queue_t *q = rq->q;
+
+        elv_completed_request(q, flush_rq);
+
+        rq->flags |= REQ_BAR_PREFLUSH;
+
+        if (!flush_rq->errors)
+                elv_requeue_request(q, rq);
+        else {
+                q->end_flush_fn(q, flush_rq);
+                clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
+                q->request_fn(q);
+        }
+}
+
+static void blk_post_flush_end_io(struct request *flush_rq)
+{
+        struct request *rq = flush_rq->end_io_data;
+        request_queue_t *q = rq->q;
+
+        elv_completed_request(q, flush_rq);
+
+        rq->flags |= REQ_BAR_POSTFLUSH;
+
+        q->end_flush_fn(q, flush_rq);
+        clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
+        q->request_fn(q);
+}
+
+struct request *blk_start_pre_flush(request_queue_t *q, struct request *rq)
+{
+        struct request *flush_rq = q->flush_rq;
+
+        BUG_ON(!blk_barrier_rq(rq));
+
+        if (test_and_set_bit(QUEUE_FLAG_FLUSH, &q->queue_flags))
+                return NULL;
+
+        rq_init(q, flush_rq);
+        flush_rq->elevator_private = NULL;
+        flush_rq->flags = REQ_BAR_FLUSH;
+        flush_rq->rq_disk = rq->rq_disk;
+        flush_rq->rl = NULL;
+
+        /*
+         * prepare_flush returns 0 if no flush is needed, just mark both
+         * pre and post flush as done in that case
+         */
+        if (!q->prepare_flush_fn(q, flush_rq)) {
+                rq->flags |= REQ_BAR_PREFLUSH | REQ_BAR_POSTFLUSH;
+                clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
+                return rq;
+        }
+
+        /*
+         * some drivers dequeue requests right away, some only after io
+         * completion. make sure the request is dequeued.
+         */
+        if (!list_empty(&rq->queuelist))
+                blkdev_dequeue_request(rq);
+
+        flush_rq->end_io_data = rq;
+        flush_rq->end_io = blk_pre_flush_end_io;
+
+        __elv_add_request(q, flush_rq, ELEVATOR_INSERT_FRONT, 0);
+        return flush_rq;
+}
+
+static void blk_start_post_flush(request_queue_t *q, struct request *rq)
+{
+        struct request *flush_rq = q->flush_rq;
+
+        BUG_ON(!blk_barrier_rq(rq));
+
+        rq_init(q, flush_rq);
+        flush_rq->elevator_private = NULL;
+        flush_rq->flags = REQ_BAR_FLUSH;
+        flush_rq->rq_disk = rq->rq_disk;
+        flush_rq->rl = NULL;
+
+        if (q->prepare_flush_fn(q, flush_rq)) {
+                flush_rq->end_io_data = rq;
+                flush_rq->end_io = blk_post_flush_end_io;
+
+                __elv_add_request(q, flush_rq, ELEVATOR_INSERT_FRONT, 0);
+                q->request_fn(q);
+        }
+}
+
+static inline int blk_check_end_barrier(request_queue_t *q, struct request *rq,
+                                        int sectors)
+{
+        if (sectors > rq->nr_sectors)
+                sectors = rq->nr_sectors;
+
+        rq->nr_sectors -= sectors;
+        return rq->nr_sectors;
+}
+
+static int __blk_complete_barrier_rq(request_queue_t *q, struct request *rq,
+                                     int sectors, int queue_locked)
+{
+        if (q->ordered != QUEUE_ORDERED_FLUSH)
+                return 0;
+        if (!blk_fs_request(rq) || !blk_barrier_rq(rq))
+                return 0;
+        if (blk_barrier_postflush(rq))
+                return 0;
+
+        if (!blk_check_end_barrier(q, rq, sectors)) {
+                unsigned long flags = 0;
+
+                if (!queue_locked)
+                        spin_lock_irqsave(q->queue_lock, flags);
+
+                blk_start_post_flush(q, rq);
+
+                if (!queue_locked)
+                        spin_unlock_irqrestore(q->queue_lock, flags);
+        }
+
+        return 1;
+}
+
+/**
+ * blk_complete_barrier_rq - complete possible barrier request
+ * @q:  the request queue for the device
+ * @rq:  the request
+ * @sectors:  number of sectors to complete
+ *
+ * Description:
+ *   Used in driver end_io handling to determine whether to postpone
+ *   completion of a barrier request until a post flush has been done. This
+ *   is the unlocked variant, used if the caller doesn't already hold the
+ *   queue lock.
+ **/
+int blk_complete_barrier_rq(request_queue_t *q, struct request *rq, int sectors)
+{
+        return __blk_complete_barrier_rq(q, rq, sectors, 0);
+}
+EXPORT_SYMBOL(blk_complete_barrier_rq);
+
+/**
+ * blk_complete_barrier_rq_locked - complete possible barrier request
+ * @q:  the request queue for the device
+ * @rq:  the request
+ * @sectors:  number of sectors to complete
+ *
+ * Description:
+ *   See blk_complete_barrier_rq(). This variant must be used if the caller
+ *   holds the queue lock.
+ **/
+int blk_complete_barrier_rq_locked(request_queue_t *q, struct request *rq,
+                                   int sectors)
+{
+        return __blk_complete_barrier_rq(q, rq, sectors, 1);
+}
+EXPORT_SYMBOL(blk_complete_barrier_rq_locked);
+
+/**
+ * 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. By default
+ *    the block layer sets this to the highest numbered "low" memory page.
+ **/
+void blk_queue_bounce_limit(request_queue_t *q, u64 dma_addr)
+{
+        unsigned long bounce_pfn = dma_addr >> PAGE_SHIFT;
+
+        /*
+         * set appropriate bounce gfp mask -- unfortunately we don't have a
+         * full 4GB zone, so we have to resort to low memory for any bounces.
+         * ISA has its own < 16MB zone.
+         */
+        if (bounce_pfn < blk_max_low_pfn) {
+                BUG_ON(dma_addr < BLK_BOUNCE_ISA);
+                init_emergency_isa_pool();
+                q->bounce_gfp = GFP_NOIO | GFP_DMA;
+        } else
+                q->bounce_gfp = GFP_NOIO;
+
+        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(request_queue_t *q, unsigned short 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);
+        }
+
+        q->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(request_queue_t *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(request_queue_t *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(request_queue_t *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(request_queue_t *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(request_queue_t *t, request_queue_t *b)
+{
+        /* zero is "infinity" */
+        t->max_sectors = t->max_hw_sectors =
+                min_not_zero(t->max_sectors,b->max_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);
+}
+
+EXPORT_SYMBOL(blk_queue_stack_limits);
+
+/**
+ * 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(request_queue_t *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(request_queue_t *q, int mask)
+{
+        q->dma_alignment = mask;
+}
+
+EXPORT_SYMBOL(blk_queue_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(request_queue_t *q, int tag)
+{
+        struct blk_queue_tag *bqt = q->queue_tags;
+
+        if (unlikely(bqt == NULL || tag >= bqt->real_max_depth))
+                return NULL;
+
+        return bqt->tag_index[tag];
+}
+
+EXPORT_SYMBOL(blk_queue_find_tag);
+
+/**
+ * __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(request_queue_t *q)
+{
+        struct blk_queue_tag *bqt = q->queue_tags;
+
+        if (!bqt)
+                return;
+
+        if (atomic_dec_and_test(&bqt->refcnt)) {
+                BUG_ON(bqt->busy);
+                BUG_ON(!list_empty(&bqt->busy_list));
+
+                kfree(bqt->tag_index);
+                bqt->tag_index = NULL;
+
+                kfree(bqt->tag_map);
+                bqt->tag_map = NULL;
+
+                kfree(bqt);
+        }
+
+        q->queue_tags = NULL;
+        q->queue_flags &= ~(1 << QUEUE_FLAG_QUEUED);
+}
+
+/**
+ * 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(request_queue_t *q)
+{
+        clear_bit(QUEUE_FLAG_QUEUED, &q->queue_flags);
+}
+
+EXPORT_SYMBOL(blk_queue_free_tags);
+
+static int
+init_tag_map(request_queue_t *q, struct blk_queue_tag *tags, int depth)
+{
+        struct request **tag_index;
+        unsigned long *tag_map;
+        int nr_ulongs;
+
+        if (depth > q->nr_requests * 2) {
+                depth = q->nr_requests * 2;
+                printk(KERN_ERR "%s: adjusted depth to %d\n",
+                                __FUNCTION__, depth);
+        }
+
+        tag_index = kmalloc(depth * sizeof(struct request *), GFP_ATOMIC);
+        if (!tag_index)
+                goto fail;
+
+        nr_ulongs = ALIGN(depth, BITS_PER_LONG) / BITS_PER_LONG;
+        tag_map = kmalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
+        if (!tag_map)
+                goto fail;
+
+        memset(tag_index, 0, depth * sizeof(struct request *));
+        memset(tag_map, 0, nr_ulongs * sizeof(unsigned long));
+        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;
+}
+
+/**
+ * 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(request_queue_t *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 = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
+                if (!tags)
+                        goto fail;
+
+                if (init_tag_map(q, tags, depth))
+                        goto fail;
+
+                INIT_LIST_HEAD(&tags->busy_list);
+                tags->busy = 0;
+                atomic_set(&tags->refcnt, 1);
+        } 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);
+        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(request_queue_t *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;
+        }
+
+        /*
+         * 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(request_queue_t *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;
+
+        if (unlikely(!__test_and_clear_bit(tag, bqt->tag_map))) {
+                printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
+                       __FUNCTION__, tag);
+                return;
+        }
+
+        list_del_init(&rq->queuelist);
+        rq->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;
+        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(request_queue_t *q, struct request *rq)
+{
+        struct blk_queue_tag *bqt = q->queue_tags;
+        int tag;
+
+        if (unlikely((rq->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();
+        }
+
+        tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth);
+        if (tag >= bqt->max_depth)
+                return 1;
+
+        __set_bit(tag, bqt->tag_map);
+
+        rq->flags |= REQ_QUEUED;
+        rq->tag = tag;
+        bqt->tag_index[tag] = rq;
+        blkdev_dequeue_request(rq);
+        list_add(&rq->queuelist, &bqt->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(request_queue_t *q)
+{
+        struct blk_queue_tag *bqt = q->queue_tags;
+        struct list_head *tmp, *n;
+        struct request *rq;
+
+        list_for_each_safe(tmp, n, &bqt->busy_list) {
+                rq = list_entry_rq(tmp);
+
+                if (rq->tag == -1) {
+                        printk(KERN_ERR
+                               "%s: bad tag found on list\n", __FUNCTION__);
+                        list_del_init(&rq->queuelist);
+                        rq->flags &= ~REQ_QUEUED;
+                } else
+                        blk_queue_end_tag(q, rq);
+
+                rq->flags &= ~REQ_STARTED;
+                __elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 0);
+        }
+}
+
+EXPORT_SYMBOL(blk_queue_invalidate_tags);
+
+static char *rq_flags[] = {
+        "REQ_RW",
+        "REQ_FAILFAST",
+        "REQ_SORTED",
+        "REQ_SOFTBARRIER",
+        "REQ_HARDBARRIER",
+        "REQ_CMD",
+        "REQ_NOMERGE",
+        "REQ_STARTED",
+        "REQ_DONTPREP",
+        "REQ_QUEUED",
+        "REQ_ELVPRIV",
+        "REQ_PC",
+        "REQ_BLOCK_PC",
+        "REQ_SENSE",
+        "REQ_FAILED",
+        "REQ_QUIET",
+        "REQ_SPECIAL",
+        "REQ_DRIVE_CMD",
+        "REQ_DRIVE_TASK",
+        "REQ_DRIVE_TASKFILE",
+        "REQ_PREEMPT",
+        "REQ_PM_SUSPEND",
+        "REQ_PM_RESUME",
+        "REQ_PM_SHUTDOWN",
+};
+
+void blk_dump_rq_flags(struct request *rq, char *msg)
+{
+        int bit;
+
+        printk("%s: dev %s: flags = ", msg,
+                rq->rq_disk ? rq->rq_disk->disk_name : "?");
+        bit = 0;
+        do {
+                if (rq->flags & (1 << bit))
+                        printk("%s ", rq_flags[bit]);
+                bit++;
+        } while (bit < __REQ_NR_BITS);
+
+        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 (rq->flags & (REQ_BLOCK_PC | REQ_PC)) {
+                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(request_queue_t *q, struct bio *bio)
+{
+        struct bio_vec *bv, *bvprv = NULL;
+        int i, nr_phys_segs, nr_hw_segs, seg_size, hw_seg_size, cluster;
+        int high, highprv = 1;
+
+        if (unlikely(!bio->bi_io_vec))
+                return;
+
+        cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+        hw_seg_size = seg_size = nr_phys_segs = nr_hw_segs = 0;
+        bio_for_each_segment(bv, bio, i) {
+                /*
+                 * 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 (hw_seg_size > bio->bi_hw_front_size)
+                                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 (hw_seg_size > bio->bi_hw_back_size)
+                bio->bi_hw_back_size = hw_seg_size;
+        if (nr_hw_segs == 1 && hw_seg_size > bio->bi_hw_front_size)
+                bio->bi_hw_front_size = hw_seg_size;
+        bio->bi_phys_segments = nr_phys_segs;
+        bio->bi_hw_segments = nr_hw_segs;
+        bio->bi_flags |= (1 << BIO_SEG_VALID);
+}
+
+
+static int blk_phys_contig_segment(request_queue_t *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(request_queue_t *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_front_size + bio->bi_hw_back_size))
+                return 0;
+        if (bio->bi_size + nxt->bi_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(request_queue_t *q, struct request *rq, struct scatterlist *sg)
+{
+        struct bio_vec *bvec, *bvprv;
+        struct bio *bio;
+        int nsegs, i, cluster;
+
+        nsegs = 0;
+        cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+
+        /*
+         * for each bio in rq
+         */
+        bvprv = NULL;
+        rq_for_each_bio(bio, rq) {
+                /*
+                 * for each segment in bio
+                 */
+                bio_for_each_segment(bvec, bio, i) {
+                        int nbytes = bvec->bv_len;
+
+                        if (bvprv && cluster) {
+                                if (sg[nsegs - 1].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[nsegs - 1].length += nbytes;
+                        } else {
+new_segment:
+                                memset(&sg[nsegs],0,sizeof(struct scatterlist));
+                                sg[nsegs].page = bvec->bv_page;
+                                sg[nsegs].length = nbytes;
+                                sg[nsegs].offset = bvec->bv_offset;
+
+                                nsegs++;
+                        }
+                        bvprv = bvec;
+                } /* segments in bio */
+        } /* bios in rq */
+
+        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(request_queue_t *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->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(request_queue_t *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->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(request_queue_t *q, struct request *req, 
+                            struct bio *bio)
+{
+        int len;
+
+        if (req->nr_sectors + bio_sectors(bio) > q->max_sectors) {
+                req->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(request_queue_t *q, struct request *req, 
+                             struct bio *bio)
+{
+        int len;
+
+        if (req->nr_sectors + bio_sectors(bio) > q->max_sectors) {
+                req->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(request_queue_t *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(request_queue_t *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 (test_bit(QUEUE_FLAG_STOPPED, &q->queue_flags))
+                return;
+
+        if (!test_and_set_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags))
+                mod_timer(&q->unplug_timer, jiffies + q->unplug_delay);
+}
+
+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(request_queue_t *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(request_queue_t *q)
+{
+        if (unlikely(test_bit(QUEUE_FLAG_STOPPED, &q->queue_flags)))
+                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 &request_queue_t 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(request_queue_t *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)
+{
+        request_queue_t *q = bdi->unplug_io_data;
+
+        /*
+         * devices don't necessarily have an ->unplug_fn defined
+         */
+        if (q->unplug_fn)
+                q->unplug_fn(q);
+}
+
+static void blk_unplug_work(void *data)
+{
+        request_queue_t *q = data;
+
+        q->unplug_fn(q);
+}
+
+static void blk_unplug_timeout(unsigned long data)
+{
+        request_queue_t *q = (request_queue_t *)data;
+
+        kblockd_schedule_work(&q->unplug_work);
+}
+
+/**
+ * blk_start_queue - restart a previously stopped queue
+ * @q:    The &request_queue_t 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(request_queue_t *q)
+{
+        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 &request_queue_t 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(request_queue_t *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
+ *     the 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();
+}
+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);
+        if (!elv_queue_empty(q))
+                q->request_fn(q);
+        spin_unlock_irqrestore(q->queue_lock, flags);
+}
+EXPORT_SYMBOL(blk_run_queue);
+
+/**
+ * blk_cleanup_queue: - release a &request_queue_t when it is no longer needed
+ * @q:    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...
+ **/
+void blk_cleanup_queue(request_queue_t * q)
+{
+        struct request_list *rl = &q->rq;
+
+        if (!atomic_dec_and_test(&q->refcnt))
+                return;
+
+        if (q->elevator)
+                elevator_exit(q->elevator);
+
+        blk_sync_queue(q);
+
+        if (rl->rq_pool)
+                mempool_destroy(rl->rq_pool);
+
+        if (q->queue_tags)
+                __blk_queue_free_tags(q);
+
+        blk_queue_ordered(q, QUEUE_ORDERED_NONE);
+
+        kmem_cache_free(requestq_cachep, q);
+}
+
+EXPORT_SYMBOL(blk_cleanup_queue);
+
+static int blk_init_free_list(request_queue_t *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;
+}
+
+static int __make_request(request_queue_t *, struct bio *);
+
+request_queue_t *blk_alloc_queue(gfp_t gfp_mask)
+{
+        return blk_alloc_queue_node(gfp_mask, -1);
+}
+EXPORT_SYMBOL(blk_alloc_queue);
+
+request_queue_t *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
+{
+        request_queue_t *q;
+
+        q = kmem_cache_alloc_node(requestq_cachep, gfp_mask, node_id);
+        if (!q)
+                return NULL;
+
+        memset(q, 0, sizeof(*q));
+        init_timer(&q->unplug_timer);
+        atomic_set(&q->refcnt, 1);
+
+        q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
+        q->backing_dev_info.unplug_io_data = q;
+
+        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.
+ *
+ *    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).
+ **/
+
+request_queue_t *blk_init_queue(request_fn_proc *rfn, spinlock_t *lock)
+{
+        return blk_init_queue_node(rfn, lock, -1);
+}
+EXPORT_SYMBOL(blk_init_queue);
+
+request_queue_t *
+blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
+{
+        request_queue_t *q = blk_alloc_queue_node(GFP_KERNEL, node_id);
+
+        if (!q)
+                return NULL;
+
+        q->node = node_id;
+        if (blk_init_free_list(q))
+                goto out_init;
+
+        /*
+         * 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->back_merge_fn        = ll_back_merge_fn;
+        q->front_merge_fn       = ll_front_merge_fn;
+        q->merge_requests_fn    = ll_merge_requests_fn;
+        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);
+
+        /*
+         * all done
+         */
+        if (!elevator_init(q, NULL)) {
+                blk_queue_congestion_threshold(q);
+                return q;
+        }
+
+        blk_cleanup_queue(q);
+out_init:
+        kmem_cache_free(requestq_cachep, q);
+        return NULL;
+}
+EXPORT_SYMBOL(blk_init_queue_node);
+
+int blk_get_queue(request_queue_t *q)
+{
+        if (likely(!test_bit(QUEUE_FLAG_DEAD, &q->queue_flags))) {
+                atomic_inc(&q->refcnt);
+                return 0;
+        }
+
+        return 1;
+}
+
+EXPORT_SYMBOL(blk_get_queue);
+
+static inline void blk_free_request(request_queue_t *q, struct request *rq)
+{
+        if (rq->flags & REQ_ELVPRIV)
+                elv_put_request(q, rq);
+        mempool_free(rq, q->rq.rq_pool);
+}
+
+static inline struct request *
+blk_alloc_request(request_queue_t *q, int rw, struct bio *bio,
+                  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->flags and bio->bi_rw,
+         * see bio.h and blkdev.h
+         */
+        rq->flags = rw;
+
+        if (priv) {
+                if (unlikely(elv_set_request(q, rq, bio, gfp_mask))) {
+                        mempool_free(rq, q->rq.rq_pool);
+                        return NULL;
+                }
+                rq->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(request_queue_t *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(request_queue_t *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(request_queue_t *q, int rw)
+{
+        struct request_list *rl = &q->rq;
+
+        if (rl->count[rw] < queue_congestion_off_threshold(q))
+                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(request_queue_t *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(request_queue_t *q, int rw, struct bio *bio,
+                                   gfp_t gfp_mask)
+{
+        struct request *rq = NULL;
+        struct request_list *rl = &q->rq;
+        struct io_context *ioc = current_io_context(GFP_ATOMIC);
+        int priv;
+
+        if (rl->count[rw]+1 >= q->nr_requests) {
+                /*
+                 * 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);
+                }
+        }
+
+        switch (elv_may_queue(q, rw, bio)) {
+                case ELV_MQUEUE_NO:
+                        goto rq_starved;
+                case ELV_MQUEUE_MAY:
+                        break;
+                case ELV_MQUEUE_MUST:
+                        goto get_rq;
+        }
+
+        if (blk_queue_full(q, rw) && !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;
+        }
+
+get_rq:
+        /*
+         * 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;
+        if (rl->count[rw] >= queue_congestion_on_threshold(q))
+                set_queue_congested(q, rw);
+
+        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, bio, priv, gfp_mask);
+        if (!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;
+        }
+
+        if (ioc_batching(q, ioc))
+                ioc->nr_batch_requests--;
+        
+        rq_init(q, rq);
+        rq->rl = rl;
+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(request_queue_t *q, int rw,
+                                        struct bio *bio)
+{
+        struct request *rq;
+
+        rq = get_request(q, rw, 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, bio, GFP_NOIO);
+
+                if (!rq) {
+                        struct io_context *ioc;
+
+                        __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);
+                        ioc_set_batching(q, ioc);
+
+                        spin_lock_irq(q->queue_lock);
+                }
+                finish_wait(&rl->wait[rw], &wait);
+        }
+
+        return rq;
+}
+
+struct request *blk_get_request(request_queue_t *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_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(request_queue_t *q, struct request *rq)
+{
+        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(request_queue_t *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->flags |= REQ_SPECIAL | 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, rq->nr_sectors, 1);
+        __elv_add_request(q, rq, where, 0);
+
+        if (blk_queue_plugged(q))
+                __generic_unplug_device(q);
+        else
+                q->request_fn(q);
+        spin_unlock_irqrestore(q->queue_lock, flags);
+}
+
+EXPORT_SYMBOL(blk_insert_request);
+
+/**
+ * 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(request_queue_t *q, struct request *rq, void __user *ubuf,
+                    unsigned int len)
+{
+        unsigned long uaddr;
+        struct bio *bio;
+        int reading;
+
+        if (len > (q->max_sectors << 9))
+                return -EINVAL;
+        if (!len || !ubuf)
+                return -EINVAL;
+
+        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)) {
+                rq->bio = rq->biotail = bio;
+                blk_rq_bio_prep(q, rq, bio);
+
+                rq->buffer = rq->data = NULL;
+                rq->data_len = len;
+                return 0;
+        }
+
+        /*
+         * bio is the err-ptr
+         */
+        return PTR_ERR(bio);
+}
+
+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
+ *
+ * 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(request_queue_t *q, struct request *rq,
+                        struct sg_iovec *iov, int iov_count)
+{
+        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);
+
+        rq->bio = rq->biotail = bio;
+        blk_rq_bio_prep(q, rq, bio);
+        rq->buffer = rq->data = NULL;
+        rq->data_len = bio->bi_size;
+        return 0;
+}
+
+EXPORT_SYMBOL(blk_rq_map_user_iov);
+
+/**
+ * blk_rq_unmap_user - unmap a request with user data
+ * @bio:        bio to be unmapped
+ * @ulen:       length of user buffer
+ *
+ * Description:
+ *    Unmap a bio previously mapped by blk_rq_map_user().
+ */
+int blk_rq_unmap_user(struct bio *bio, unsigned int ulen)
+{
+        int ret = 0;
+
+        if (bio) {
+                if (bio_flagged(bio, BIO_USER_MAPPED))
+                        bio_unmap_user(bio);
+                else
+                        ret = bio_uncopy_user(bio);
+        }
+
+        return 0;
+}
+
+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(request_queue_t *q, struct request *rq, void *kbuf,
+                    unsigned int len, gfp_t gfp_mask)
+{
+        struct bio *bio;
+
+        if (len > (q->max_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);
+
+        rq->bio = rq->biotail = bio;
+        blk_rq_bio_prep(q, rq, bio);
+
+        rq->buffer = rq->data = NULL;
+        rq->data_len = len;
+        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(request_queue_t *q, struct gendisk *bd_disk,
+                           struct request *rq, int at_head,
+                           void (*done)(struct request *))
+{
+        int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
+
+        rq->rq_disk = bd_disk;
+        rq->flags |= REQ_NOMERGE;
+        rq->end_io = done;
+        elv_add_request(q, rq, where, 1);
+        generic_unplug_device(q);
+}
+
+/**
+ * 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(request_queue_t *q, struct gendisk *bd_disk,
+                   struct request *rq, int at_head)
+{
+        DECLARE_COMPLETION(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->waiting = &wait;
+        blk_execute_rq_nowait(q, bd_disk, rq, at_head, blk_end_sync_rq);
+        wait_for_completion(&wait);
+        rq->waiting = NULL;
+
+        if (rq->errors)
+                err = -EIO;
+
+        return err;
+}
+
+EXPORT_SYMBOL(blk_execute_rq);
+
+/**
+ * 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)
+{
+        request_queue_t *q;
+
+        if (bdev->bd_disk == NULL)
+                return -ENXIO;
+
+        q = bdev_get_queue(bdev);
+        if (!q)
+                return -ENXIO;
+        if (!q->issue_flush_fn)
+                return -EOPNOTSUPP;
+
+        return q->issue_flush_fn(q, bdev->bd_disk, error_sector);
+}
+
+EXPORT_SYMBOL(blkdev_issue_flush);
+
+static void drive_stat_acct(struct request *rq, int nr_sectors, 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(request_queue_t * q, struct request * req)
+{
+        drive_stat_acct(req, req->nr_sectors, 1);
+
+        if (q->activity_fn)
+                q->activity_fn(q->activity_data, rq_data_dir(req));
+
+        /*
+         * 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;
+}
+
+/*
+ * queue lock must be held
+ */
+static void __blk_put_request(request_queue_t *q, struct request *req)
+{
+        struct request_list *rl = req->rl;
+
+        if (unlikely(!q))
+                return;
+        if (unlikely(--req->ref_count))
+                return;
+
+        elv_completed_request(q, req);
+
+        req->rq_status = RQ_INACTIVE;
+        req->rl = NULL;
+
+        /*
+         * Request may not have originated from ll_rw_blk. if not,
+         * it didn't come out of our reserved rq pools
+         */
+        if (rl) {
+                int rw = rq_data_dir(req);
+                int priv = req->flags & REQ_ELVPRIV;
+
+                BUG_ON(!list_empty(&req->queuelist));
+
+                blk_free_request(q, req);
+                freed_request(q, rw, priv);
+        }
+}
+
+void blk_put_request(struct request *req)
+{
+        unsigned long flags;
+        request_queue_t *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
+ */
+void blk_end_sync_rq(struct request *rq)
+{
+        struct completion *waiting = rq->waiting;
+
+        rq->waiting = 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);
+
+/**
+ * blk_congestion_wait - wait for a queue to become uncongested
+ * @rw: READ or WRITE
+ * @timeout: timeout in jiffies
+ *
+ * Waits for up to @timeout jiffies for a queue (any queue) to exit congestion.
+ * If no queues are congested then just wait for the next request to be
+ * returned.
+ */
+long blk_congestion_wait(int rw, long timeout)
+{
+        long ret;
+        DEFINE_WAIT(wait);
+        wait_queue_head_t *wqh = &congestion_wqh[rw];
+
+        prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
+        ret = io_schedule_timeout(timeout);
+        finish_wait(wqh, &wait);
+        return ret;
+}
+
+EXPORT_SYMBOL(blk_congestion_wait);
+
+/*
+ * Has to be called with the request spinlock acquired
+ */
+static int attempt_merge(request_queue_t *q, struct request *req,
+                          struct request *next)
+{
+        if (!rq_mergeable(req) || !rq_mergeable(next))
+                return 0;
+
+        /*
+         * not contigious
+         */
+        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->waiting || 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 (!q->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(request_queue_t *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(request_queue_t *q, struct request *rq)
+{
+        struct request *prev = elv_former_request(q, rq);
+
+        if (prev)
+                return attempt_merge(q, prev, rq);
+
+        return 0;
+}
+
+/**
+ * blk_attempt_remerge  - attempt to remerge active head with next request
+ * @q:    The &request_queue_t belonging to the device
+ * @rq:   The head request (usually)
+ *
+ * Description:
+ *    For head-active devices, the queue can easily be unplugged so quickly
+ *    that proper merging is not done on the front request. This may hurt
+ *    performance greatly for some devices. The block layer cannot safely
+ *    do merging on that first request for these queues, but the driver can
+ *    call this function and make it happen any way. Only the driver knows
+ *    when it is safe to do so.
+ **/
+void blk_attempt_remerge(request_queue_t *q, struct request *rq)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(q->queue_lock, flags);
+        attempt_back_merge(q, rq);
+        spin_unlock_irqrestore(q->queue_lock, flags);
+}
+
+EXPORT_SYMBOL(blk_attempt_remerge);
+
+static int __make_request(request_queue_t *q, struct bio *bio)
+{
+        struct request *req;
+        int el_ret, rw, nr_sectors, cur_nr_sectors, barrier, err, sync;
+        unsigned short prio;
+        sector_t sector;
+
+        sector = bio->bi_sector;
+        nr_sectors = bio_sectors(bio);
+        cur_nr_sectors = bio_cur_sectors(bio);
+        prio = bio_prio(bio);
+
+        rw = bio_data_dir(bio);
+        sync = bio_sync(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);
+
+        spin_lock_prefetch(q->queue_lock);
+
+        barrier = bio_barrier(bio);
+        if (unlikely(barrier) && (q->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 (!q->back_merge_fn(q, req, bio))
+                                break;
+
+                        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, nr_sectors, 0);
+                        if (!attempt_back_merge(q, req))
+                                elv_merged_request(q, req);
+                        goto out;
+
+                case ELEVATOR_FRONT_MERGE:
+                        BUG_ON(!rq_mergeable(req));
+
+                        if (!q->front_merge_fn(q, req, bio))
+                                break;
+
+                        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 = cur_nr_sectors;
+                        req->hard_cur_sectors = cur_nr_sectors;
+                        req->sector = req->hard_sector = sector;
+                        req->nr_sectors = req->hard_nr_sectors += nr_sectors;
+                        req->ioprio = ioprio_best(req->ioprio, prio);
+                        drive_stat_acct(req, nr_sectors, 0);
+                        if (!attempt_front_merge(q, req))
+                                elv_merged_request(q, req);
+                        goto out;
+
+                /* ELV_NO_MERGE: elevator says don't/can't merge. */
+                default:
+                        ;
+        }
+
+get_rq:
+        /*
+         * Grab a free request. This is might sleep but can not fail.
+         * Returns with the queue unlocked.
+         */
+        req = get_request_wait(q, rw, 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.
+         */
+
+        req->flags |= REQ_CMD;
+
+        /*
+         * inherit FAILFAST from bio (for read-ahead, and explicit FAILFAST)
+         */
+        if (bio_rw_ahead(bio) || bio_failfast(bio))
+                req->flags |= REQ_FAILFAST;
+
+        /*
+         * REQ_BARRIER implies no merging, but lets make it explicit
+         */
+        if (unlikely(barrier))
+                req->flags |= (REQ_HARDBARRIER | REQ_NOMERGE);
+
+        req->errors = 0;
+        req->hard_sector = req->sector = sector;
+        req->hard_nr_sectors = req->nr_sectors = nr_sectors;
+        req->current_nr_sectors = req->hard_cur_sectors = cur_nr_sectors;
+        req->nr_phys_segments = bio_phys_segments(q, bio);
+        req->nr_hw_segments = bio_hw_segments(q, bio);
+        req->buffer = bio_data(bio);    /* see ->buffer comment above */
+        req->waiting = NULL;
+        req->bio = req->biotail = bio;
+        req->ioprio = prio;
+        req->rq_disk = bio->bi_bdev->bd_disk;
+        req->start_time = jiffies;
+
+        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, nr_sectors << 9, 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 (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;
+        }
+}
+
+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);
+}
+
+/**
+ * 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.
+ */
+void generic_make_request(struct bio *bio)
+{
+        request_queue_t *q;
+        sector_t maxsector;
+        int ret, nr_sectors = bio_sectors(bio);
+
+        might_sleep();
+        /* 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);
+                        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.
+         */
+        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, bio->bi_size, -EIO);
+                        break;
+                }
+
+                if (unlikely(bio_sectors(bio) > 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 this device has partitions, remap block n
+                 * of partition p to block n+start(p) of the disk.
+                 */
+                blk_partition_remap(bio);
+
+                ret = q->make_request_fn(q, bio);
+        } while (ret);
+}
+
+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_BUG_ON(!bio->bi_size);
+        BIO_BUG_ON(!bio->bi_io_vec);
+        bio->bi_rw |= rw;
+        if (rw & WRITE)
+                mod_page_state(pgpgout, count);
+        else
+                mod_page_state(pgpgin, count);
+
+        if (unlikely(block_dump)) {
+                char b[BDEVNAME_SIZE];
+                printk(KERN_DEBUG "%s(%d): %s block %Lu on %s\n",
+                        current->comm, current->pid,
+                        (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_segments(struct request *rq)
+{
+        struct bio *bio, *prevbio = NULL;
+        int nr_phys_segs, nr_hw_segs;
+        unsigned int phys_size, hw_size;
+        request_queue_t *q = rq->q;
+
+        if (!rq->bio)
+                return;
+
+        phys_size = hw_size = nr_phys_segs = nr_hw_segs = 0;
+        rq_for_each_bio(bio, rq) {
+                /* Force bio hw/phys segs to be recalculated. */
+                bio->bi_flags &= ~(1 << BIO_SEG_VALID);
+
+                nr_phys_segs += bio_phys_segments(q, bio);
+                nr_hw_segs += bio_hw_segments(q, bio);
+                if (prevbio) {
+                        int pseg = phys_size + prevbio->bi_size + bio->bi_size;
+                        int hseg = hw_size + prevbio->bi_size + bio->bi_size;
+
+                        if (blk_phys_contig_segment(q, prevbio, bio) &&
+                            pseg <= q->max_segment_size) {
+                                nr_phys_segs--;
+                                phys_size += prevbio->bi_size + bio->bi_size;
+                        } else
+                                phys_size = 0;
+
+                        if (blk_hw_contig_segment(q, prevbio, bio) &&
+                            hseg <= q->max_segment_size) {
+                                nr_hw_segs--;
+                                hw_size += prevbio->bi_size + bio->bi_size;
+                        } else
+                                hw_size = 0;
+                }
+                prevbio = bio;
+        }
+
+        rq->nr_phys_segments = nr_phys_segs;
+        rq->nr_hw_segments = nr_hw_segs;
+}
+
+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;
+                }
+        }
+}
+
+static int __end_that_request_first(struct request *req, int uptodate,
+                                    int nr_bytes)
+{
+        int total_bytes, bio_nbytes, error, next_idx = 0;
+        struct bio *bio;
+
+        /*
+         * extend uptodate bool to allow < 0 value to be direct io error
+         */
+        error = 0;
+        if (end_io_error(uptodate))
+                error = !uptodate ? -EIO : uptodate;
+
+        /*
+         * 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 (!uptodate) {
+                if (blk_fs_request(req) && !(req->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;
+
+                if (nr_bytes >= bio->bi_size) {
+                        req->bio = bio->bi_next;
+                        nbytes = bio->bi_size;
+                        bio_endio(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) {
+                bio_endio(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;
+}
+
+/**
+ * end_that_request_first - end I/O on a request
+ * @req:      the request being processed
+ * @uptodate: 1 for success, 0 for I/O error, < 0 for specific error
+ * @nr_sectors: number of sectors to end I/O on
+ *
+ * Description:
+ *     Ends I/O on a number of sectors 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
+ **/
+int end_that_request_first(struct request *req, int uptodate, int nr_sectors)
+{
+        return __end_that_request_first(req, uptodate, nr_sectors << 9);
+}
+
+EXPORT_SYMBOL(end_that_request_first);
+
+/**
+ * end_that_request_chunk - end I/O on a request
+ * @req:      the request being processed
+ * @uptodate: 1 for success, 0 for I/O error, < 0 for specific 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). Like end_that_request_first(),
+ *     but deals with bytes instead of sectors.
+ *
+ * Return:
+ *     0 - we are done with this request, call end_that_request_last()
+ *     1 - still buffers pending for this request
+ **/
+int end_that_request_chunk(struct request *req, int uptodate, int nr_bytes)
+{
+        return __end_that_request_first(req, uptodate, nr_bytes);
+}
+
+EXPORT_SYMBOL(end_that_request_chunk);
+
+/*
+ * queue lock must be held
+ */
+void end_that_request_last(struct request *req)
+{
+        struct gendisk *disk = req->rq_disk;
+
+        if (unlikely(laptop_mode) && blk_fs_request(req))
+                laptop_io_completion();
+
+        if (disk && blk_fs_request(req)) {
+                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);
+        else
+                __blk_put_request(req->q, req);
+}
+
+EXPORT_SYMBOL(end_that_request_last);
+
+void end_request(struct request *req, int uptodate)
+{
+        if (!end_that_request_first(req, uptodate, req->hard_cur_sectors)) {
+                add_disk_randomness(req->rq_disk);
+                blkdev_dequeue_request(req);
+                end_that_request_last(req);
+        }
+}
+
+EXPORT_SYMBOL(end_request);
+
+void blk_rq_bio_prep(request_queue_t *q, struct request *rq, struct bio *bio)
+{
+        /* first three bits are identical in rq->flags and bio->bi_rw */
+        rq->flags |= (bio->bi_rw & 7);
+
+        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->bio = rq->biotail = bio;
+}
+
+EXPORT_SYMBOL(blk_rq_bio_prep);
+
+int kblockd_schedule_work(struct work_struct *work)
+{
+        return queue_work(kblockd_workqueue, work);
+}
+
+EXPORT_SYMBOL(kblockd_schedule_work);
+
+void kblockd_flush(void)
+{
+        flush_workqueue(kblockd_workqueue);
+}
+EXPORT_SYMBOL(kblockd_flush);
+
+int __init blk_dev_init(void)
+{
+        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, NULL);
+
+        requestq_cachep = kmem_cache_create("blkdev_queue",
+                        sizeof(request_queue_t), 0, SLAB_PANIC, NULL, NULL);
+
+        iocontext_cachep = kmem_cache_create("blkdev_ioc",
+                        sizeof(struct io_context), 0, SLAB_PANIC, NULL, NULL);
+
+        blk_max_low_pfn = max_low_pfn;
+        blk_max_pfn = max_pfn;
+
+        return 0;
+}
+
+/*
+ * IO Context helper functions
+ */
+void put_io_context(struct io_context *ioc)
+{
+        if (ioc == NULL)
+                return;
+
+        BUG_ON(atomic_read(&ioc->refcount) == 0);
+
+        if (atomic_dec_and_test(&ioc->refcount)) {
+                if (ioc->aic && ioc->aic->dtor)
+                        ioc->aic->dtor(ioc->aic);
+                if (ioc->cic && ioc->cic->dtor)
+                        ioc->cic->dtor(ioc->cic);
+
+                kmem_cache_free(iocontext_cachep, ioc);
+        }
+}
+EXPORT_SYMBOL(put_io_context);
+
+/* Called by the exitting task */
+void exit_io_context(void)
+{
+        unsigned long flags;
+        struct io_context *ioc;
+
+        local_irq_save(flags);
+        task_lock(current);
+        ioc = current->io_context;
+        current->io_context = NULL;
+        ioc->task = NULL;
+        task_unlock(current);
+        local_irq_restore(flags);
+
+        if (ioc->aic && ioc->aic->exit)
+                ioc->aic->exit(ioc->aic);
+        if (ioc->cic && ioc->cic->exit)
+                ioc->cic->exit(ioc->cic);
+
+        put_io_context(ioc);
+}
+
+/*
+ * 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.
+ */
+struct io_context *current_io_context(gfp_t gfp_flags)
+{
+        struct task_struct *tsk = current;
+        struct io_context *ret;
+
+        ret = tsk->io_context;
+        if (likely(ret))
+                return ret;
+
+        ret = kmem_cache_alloc(iocontext_cachep, gfp_flags);
+        if (ret) {
+                atomic_set(&ret->refcount, 1);
+                ret->task = current;
+                ret->set_ioprio = NULL;
+                ret->last_waited = jiffies; /* doesn't matter... */
+                ret->nr_batch_requests = 0; /* because this is 0 */
+                ret->aic = NULL;
+                ret->cic = NULL;
+                tsk->io_context = ret;
+        }
+
+        return ret;
+}
+EXPORT_SYMBOL(current_io_context);
+
+/*
+ * 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)
+{
+        struct io_context *ret;
+        ret = current_io_context(gfp_flags);
+        if (likely(ret))
+                atomic_inc(&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;
+
+        int ret = queue_var_store(&q->nr_requests, page, count);
+        if (q->nr_requests < BLKDEV_MIN_RQ)
+                q->nr_requests = BLKDEV_MIN_RQ;
+        blk_queue_congestion_threshold(q);
+
+        if (rl->count[READ] >= queue_congestion_on_threshold(q))
+                set_queue_congested(q, READ);
+        else if (rl->count[READ] < queue_congestion_off_threshold(q))
+                clear_queue_congested(q, READ);
+
+        if (rl->count[WRITE] >= queue_congestion_on_threshold(q))
+                set_queue_congested(q, WRITE);
+        else if (rl->count[WRITE] < queue_congestion_off_threshold(q))
+                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]);
+        }
+        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);
+        if (ra_kb > (q->max_sectors >> 1))
+                ra_kb = (q->max_sectors >> 1);
+
+        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);
+        int ra_kb;
+
+        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);
+        /*
+         * Trim readahead window as well, if necessary:
+         */
+        ra_kb = q->backing_dev_info.ra_pages << (PAGE_CACHE_SHIFT - 10);
+        if (ra_kb > max_sectors_kb)
+                q->backing_dev_info.ra_pages =
+                                max_sectors_kb >> (PAGE_CACHE_SHIFT - 10);
+
+        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;
+
+        q = container_of(kobj, struct request_queue, kobj);
+        if (!entry->show)
+                return -EIO;
+
+        return entry->show(q, page);
+}
+
+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;
+
+        q = container_of(kobj, struct request_queue, kobj);
+        if (!entry->store)
+                return -EIO;
+
+        return entry->store(q, page, length);
+}
+
+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,
+};
+
+int blk_register_queue(struct gendisk *disk)
+{
+        int ret;
+
+        request_queue_t *q = disk->queue;
+
+        if (!q || !q->request_fn)
+                return -ENXIO;
+
+        q->kobj.parent = kobject_get(&disk->kobj);
+        if (!q->kobj.parent)
+                return -EBUSY;
+
+        snprintf(q->kobj.name, KOBJ_NAME_LEN, "%s", "queue");
+        q->kobj.ktype = &queue_ktype;
+
+        ret = kobject_register(&q->kobj);
+        if (ret < 0)
+                return ret;
+
+        ret = elv_register_queue(q);
+        if (ret) {
+                kobject_unregister(&q->kobj);
+                return ret;
+        }
+
+        return 0;
+}
+
+void blk_unregister_queue(struct gendisk *disk)
+{
+        request_queue_t *q = disk->queue;
+
+        if (q && q->request_fn) {
+                elv_unregister_queue(q);
+
+                kobject_unregister(&q->kobj);
+                kobject_put(&disk->kobj);
+        }
+}