1 files changed, 759 insertions, 0 deletions

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
new file mode 100644
index 000000000000..59a2bae0f35e
--- /dev/null
+++ b/drivers/block/xen-blkback/blkback.c
@@ -0,0 +1,759 @@
+/******************************************************************************
+ *
+ * Back-end of the driver for virtual block devices. This portion of the
+ * driver exports a 'unified' block-device interface that can be accessed
+ * by any operating system that implements a compatible front end. A
+ * reference front-end implementation can be found in:
+ *  drivers/block/xen-blkfront.c
+ *
+ * Copyright (c) 2003-2004, Keir Fraser & Steve Hand
+ * Copyright (c) 2005, Christopher Clark
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <linux/spinlock.h>
+#include <linux/kthread.h>
+#include <linux/list.h>
+#include <linux/delay.h>
+#include <linux/freezer.h>
+
+#include <xen/events.h>
+#include <xen/page.h>
+#include <asm/xen/hypervisor.h>
+#include <asm/xen/hypercall.h>
+#include "common.h"
+
+#define WRITE_BARRIER   (REQ_WRITE | REQ_FLUSH | REQ_FUA)
+
+/*
+ * These are rather arbitrary. They are fairly large because adjacent requests
+ * pulled from a communication ring are quite likely to end up being part of
+ * the same scatter/gather request at the disc.
+ *
+ * ** TRY INCREASING 'blkif_reqs' IF WRITE SPEEDS SEEM TOO LOW **
+ *
+ * This will increase the chances of being able to write whole tracks.
+ * 64 should be enough to keep us competitive with Linux.
+ */
+static int blkif_reqs = 64;
+module_param_named(reqs, blkif_reqs, int, 0);
+MODULE_PARM_DESC(reqs, "Number of blkback requests to allocate");
+
+/* Run-time switchable: /sys/module/blkback/parameters/ */
+static unsigned int log_stats;
+static unsigned int debug_lvl;
+module_param(log_stats, int, 0644);
+module_param(debug_lvl, int, 0644);
+
+/*
+ * Each outstanding request that we've passed to the lower device layers has a
+ * 'pending_req' allocated to it. Each buffer_head that completes decrements
+ * the pendcnt towards zero. When it hits zero, the specified domain has a
+ * response queued for it, with the saved 'id' passed back.
+ */
+struct pending_req {
+        struct blkif_st       *blkif;
+        u64            id;
+        int            nr_pages;
+        atomic_t       pendcnt;
+        unsigned short operation;
+        int            status;
+        struct list_head free_list;
+};
+
+#define BLKBACK_INVALID_HANDLE (~0)
+
+struct xen_blkbk {
+        struct pending_req      *pending_reqs;
+        /* List of all 'pending_req' available */
+        struct list_head        pending_free;
+        /* And its spinlock. */
+        spinlock_t              pending_free_lock;
+        wait_queue_head_t       pending_free_wq;
+        /* The list of all pages that are available. */
+        struct page             **pending_pages;
+        /* And the grant handles that are available. */
+        grant_handle_t          *pending_grant_handles;
+};
+
+static struct xen_blkbk *blkbk;
+
+/*
+ * Little helpful macro to figure out the index and virtual address of the
+ * pending_pages[..]. For each 'pending_req' we have have up to
+ * BLKIF_MAX_SEGMENTS_PER_REQUEST (11) pages. The seg would be from 0 through
+ * 10 and would index in the pending_pages[..]. */
+static inline int vaddr_pagenr(struct pending_req *req, int seg)
+{
+        return (req - blkbk->pending_reqs) *
+                BLKIF_MAX_SEGMENTS_PER_REQUEST + seg;
+}
+
+#define pending_page(req, seg) pending_pages[vaddr_pagenr(req, seg)]
+
+static inline unsigned long vaddr(struct pending_req *req, int seg)
+{
+        unsigned long pfn = page_to_pfn(blkbk->pending_page(req, seg));
+        return (unsigned long)pfn_to_kaddr(pfn);
+}
+
+#define pending_handle(_req, _seg) \
+        (blkbk->pending_grant_handles[vaddr_pagenr(_req, _seg)])
+
+
+static int do_block_io_op(struct blkif_st *blkif);
+static void dispatch_rw_block_io(struct blkif_st *blkif,
+                                 struct blkif_request *req,
+                                 struct pending_req *pending_req);
+static void make_response(struct blkif_st *blkif, u64 id,
+                          unsigned short op, int st);
+
+/*
+ * Retrieve from the 'pending_reqs' a free pending_req structure to be used.
+ */
+static struct pending_req *alloc_req(void)
+{
+        struct pending_req *req = NULL;
+        unsigned long flags;
+
+        spin_lock_irqsave(&blkbk->pending_free_lock, flags);
+        if (!list_empty(&blkbk->pending_free)) {
+                req = list_entry(blkbk->pending_free.next, struct pending_req,
+                                 free_list);
+                list_del(&req->free_list);
+        }
+        spin_unlock_irqrestore(&blkbk->pending_free_lock, flags);
+        return req;
+}
+
+/*
+ * Return the 'pending_req' structure back to the freepool. We also
+ * wake up the thread if it was waiting for a free page.
+ */
+static void free_req(struct pending_req *req)
+{
+        unsigned long flags;
+        int was_empty;
+
+        spin_lock_irqsave(&blkbk->pending_free_lock, flags);
+        was_empty = list_empty(&blkbk->pending_free);
+        list_add(&req->free_list, &blkbk->pending_free);
+        spin_unlock_irqrestore(&blkbk->pending_free_lock, flags);
+        if (was_empty)
+                wake_up(&blkbk->pending_free_wq);
+}
+
+/*
+ * Notification from the guest OS.
+ */
+static void blkif_notify_work(struct blkif_st *blkif)
+{
+        blkif->waiting_reqs = 1;
+        wake_up(&blkif->wq);
+}
+
+irqreturn_t blkif_be_int(int irq, void *dev_id)
+{
+        blkif_notify_work(dev_id);
+        return IRQ_HANDLED;
+}
+
+/*
+ * SCHEDULER FUNCTIONS
+ */
+
+static void print_stats(struct blkif_st *blkif)
+{
+        printk(KERN_DEBUG "%s: oo %3d  |  rd %4d  |  wr %4d  |  br %4d\n",
+               current->comm, blkif->st_oo_req,
+               blkif->st_rd_req, blkif->st_wr_req, blkif->st_br_req);
+        blkif->st_print = jiffies + msecs_to_jiffies(10 * 1000);
+        blkif->st_rd_req = 0;
+        blkif->st_wr_req = 0;
+        blkif->st_oo_req = 0;
+}
+
+int blkif_schedule(void *arg)
+{
+        struct blkif_st *blkif = arg;
+        struct vbd *vbd = &blkif->vbd;
+
+        blkif_get(blkif);
+
+        if (debug_lvl)
+                printk(KERN_DEBUG "%s: started\n", current->comm);
+
+        while (!kthread_should_stop()) {
+                if (try_to_freeze())
+                        continue;
+                if (unlikely(vbd->size != vbd_size(vbd)))
+                        vbd_resize(blkif);
+
+                wait_event_interruptible(
+                        blkif->wq,
+                        blkif->waiting_reqs || kthread_should_stop());
+                wait_event_interruptible(
+                        blkbk->pending_free_wq,
+                        !list_empty(&blkbk->pending_free) ||
+                        kthread_should_stop());
+
+                blkif->waiting_reqs = 0;
+                smp_mb(); /* clear flag *before* checking for work */
+
+                if (do_block_io_op(blkif))
+                        blkif->waiting_reqs = 1;
+
+                if (log_stats && time_after(jiffies, blkif->st_print))
+                        print_stats(blkif);
+        }
+
+        if (log_stats)
+                print_stats(blkif);
+        if (debug_lvl)
+                printk(KERN_DEBUG "%s: exiting\n", current->comm);
+
+        blkif->xenblkd = NULL;
+        blkif_put(blkif);
+
+        return 0;
+}
+
+struct seg_buf {
+        unsigned long buf;
+        unsigned int nsec;
+};
+/*
+ * Unmap the grant references, and also remove the M2P over-rides
+ * used in the 'pending_req'.
+*/
+static void xen_blkbk_unmap(struct pending_req *req)
+{
+        struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+        unsigned int i, invcount = 0;
+        grant_handle_t handle;
+        int ret;
+
+        for (i = 0; i < req->nr_pages; i++) {
+                handle = pending_handle(req, i);
+                if (handle == BLKBACK_INVALID_HANDLE)
+                        continue;
+                gnttab_set_unmap_op(&unmap[invcount], vaddr(req, i),
+                                    GNTMAP_host_map, handle);
+                pending_handle(req, i) = BLKBACK_INVALID_HANDLE;
+                invcount++;
+        }
+
+        ret = HYPERVISOR_grant_table_op(
+                GNTTABOP_unmap_grant_ref, unmap, invcount);
+        BUG_ON(ret);
+        /* Note, we use invcount, so nr->pages, so we can't index
+         * using vaddr(req, i).
+         */
+        for (i = 0; i < invcount; i++) {
+                ret = m2p_remove_override(
+                        virt_to_page(unmap[i].host_addr), false);
+                if (ret) {
+                        printk(KERN_ALERT "Failed to remove M2P override for " \
+                                "%lx\n", (unsigned long)unmap[i].host_addr);
+                        continue;
+                }
+        }
+}
+static int xen_blkbk_map(struct blkif_request *req, struct pending_req *pending_req,
+                         struct seg_buf seg[])
+{
+        struct gnttab_map_grant_ref map[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+        int i;
+        int nseg = req->nr_segments;
+        int ret = 0;
+        /* Fill out preq.nr_sects with proper amount of sectors, and setup
+         * assign map[..] with the PFN of the page in our domain with the
+         * corresponding grant reference for each page.
+         */
+        for (i = 0; i < nseg; i++) {
+                uint32_t flags;
+
+                flags = GNTMAP_host_map;
+                if (pending_req->operation != BLKIF_OP_READ)
+                        flags |= GNTMAP_readonly;
+                gnttab_set_map_op(&map[i], vaddr(pending_req, i), flags,
+                                  req->u.rw.seg[i].gref, pending_req->blkif->domid);
+        }
+
+        ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map, nseg);
+        BUG_ON(ret);
+
+        /* Now swizzel the MFN in our domain with the MFN from the other domain
+         * so that when we access vaddr(pending_req,i) it has the contents of
+         * the page from the other domain.
+         */
+        for (i = 0; i < nseg; i++) {
+                if (unlikely(map[i].status != 0)) {
+                        DPRINTK("invalid buffer -- could not remap it\n");
+                        map[i].handle = BLKBACK_INVALID_HANDLE;
+                        ret |= 1;
+                }
+
+                pending_handle(pending_req, i) = map[i].handle;
+
+                if (ret)
+                        continue;
+
+                ret = m2p_add_override(PFN_DOWN(map[i].dev_bus_addr),
+                        blkbk->pending_page(pending_req, i), false);
+                if (ret) {
+                        printk(KERN_ALERT "Failed to install M2P override for"\
+                                " %lx (ret: %d)\n", (unsigned long)
+                                map[i].dev_bus_addr, ret);
+                        /* We could switch over to GNTTABOP_copy */
+                        continue;
+                }
+
+                seg[i].buf  = map[i].dev_bus_addr |
+                        (req->u.rw.seg[i].first_sect << 9);
+        }
+        return ret;
+}
+
+/*
+ * Completion callback on the bio's. Called as bh->b_end_io()
+ */
+
+static void __end_block_io_op(struct pending_req *pending_req, int error)
+{
+        /* An error fails the entire request. */
+        if ((pending_req->operation == BLKIF_OP_WRITE_BARRIER) &&
+            (error == -EOPNOTSUPP)) {
+                DPRINTK("blkback: write barrier op failed, not supported\n");
+                blkback_barrier(XBT_NIL, pending_req->blkif->be, 0);
+                pending_req->status = BLKIF_RSP_EOPNOTSUPP;
+        } else if (error) {
+                DPRINTK("Buffer not up-to-date at end of operation, "
+                        "error=%d\n", error);
+                pending_req->status = BLKIF_RSP_ERROR;
+        }
+
+        /* If all of the bio's have completed it is time to unmap
+         * the grant references associated with 'request' and provide
+         * the proper response on the ring.
+         */
+        if (atomic_dec_and_test(&pending_req->pendcnt)) {
+                xen_blkbk_unmap(pending_req);
+                make_response(pending_req->blkif, pending_req->id,
+                              pending_req->operation, pending_req->status);
+                blkif_put(pending_req->blkif);
+                free_req(pending_req);
+        }
+}
+
+/*
+ * bio callback.
+ */
+static void end_block_io_op(struct bio *bio, int error)
+{
+        __end_block_io_op(bio->bi_private, error);
+        bio_put(bio);
+}
+
+
+
+/*
+ * Function to copy the from the ring buffer the 'struct blkif_request'
+ * (which has the sectors we want, number of them, grant references, etc),
+ * and transmute  it to the block API to hand it over to the proper block disk.
+ */
+static int do_block_io_op(struct blkif_st *blkif)
+{
+        union blkif_back_rings *blk_rings = &blkif->blk_rings;
+        struct blkif_request req;
+        struct pending_req *pending_req;
+        RING_IDX rc, rp;
+        int more_to_do = 0;
+
+        rc = blk_rings->common.req_cons;
+        rp = blk_rings->common.sring->req_prod;
+        rmb(); /* Ensure we see queued requests up to 'rp'. */
+
+        while (rc != rp) {
+
+                if (RING_REQUEST_CONS_OVERFLOW(&blk_rings->common, rc))
+                        break;
+
+                if (kthread_should_stop()) {
+                        more_to_do = 1;
+                        break;
+                }
+
+                pending_req = alloc_req();
+                if (NULL == pending_req) {
+                        blkif->st_oo_req++;
+                        more_to_do = 1;
+                        break;
+                }
+
+                switch (blkif->blk_protocol) {
+                case BLKIF_PROTOCOL_NATIVE:
+                        memcpy(&req, RING_GET_REQUEST(&blk_rings->native, rc), sizeof(req));
+                        break;
+                case BLKIF_PROTOCOL_X86_32:
+                        blkif_get_x86_32_req(&req, RING_GET_REQUEST(&blk_rings->x86_32, rc));
+                        break;
+                case BLKIF_PROTOCOL_X86_64:
+                        blkif_get_x86_64_req(&req, RING_GET_REQUEST(&blk_rings->x86_64, rc));
+                        break;
+                default:
+                        BUG();
+                }
+                blk_rings->common.req_cons = ++rc; /* before make_response() */
+
+                /* Apply all sanity checks to /private copy/ of request. */
+                barrier();
+
+                switch (req.operation) {
+                case BLKIF_OP_READ:
+                        blkif->st_rd_req++;
+                        dispatch_rw_block_io(blkif, &req, pending_req);
+                        break;
+                case BLKIF_OP_WRITE_BARRIER:
+                        blkif->st_br_req++;
+                        /* fall through */
+                case BLKIF_OP_WRITE:
+                        blkif->st_wr_req++;
+                        dispatch_rw_block_io(blkif, &req, pending_req);
+                        break;
+                default:
+                        /* A good sign something is wrong: sleep for a while to
+                         * avoid excessive CPU consumption by a bad guest. */
+                        msleep(1);
+                        DPRINTK("error: unknown block io operation [%d]\n",
+                                req.operation);
+                        make_response(blkif, req.id, req.operation,
+                                      BLKIF_RSP_ERROR);
+                        free_req(pending_req);
+                        break;
+                }
+
+                /* Yield point for this unbounded loop. */
+                cond_resched();
+        }
+
+        return more_to_do;
+}
+
+/*
+ * Transumation of the 'struct blkif_request' to a proper 'struct bio'
+ * and call the 'submit_bio' to pass it to the underlaying storage.
+ */
+static void dispatch_rw_block_io(struct blkif_st *blkif,
+                                 struct blkif_request *req,
+                                 struct pending_req *pending_req)
+{
+        struct phys_req preq;
+        struct seg_buf seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+        unsigned int nseg;
+        struct bio *bio = NULL;
+        struct bio *biolist[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+        int i, nbio = 0;
+        int operation;
+        struct blk_plug plug;
+
+        switch (req->operation) {
+        case BLKIF_OP_READ:
+                operation = READ;
+                break;
+        case BLKIF_OP_WRITE:
+                operation = WRITE;
+                break;
+        case BLKIF_OP_WRITE_BARRIER:
+                operation = WRITE_BARRIER;
+                break;
+        default:
+                operation = 0; /* make gcc happy */
+                BUG();
+        }
+
+        /* Check that the number of segments is sane. */
+        nseg = req->nr_segments;
+        if (unlikely(nseg == 0 && operation != WRITE_BARRIER) ||
+            unlikely(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
+                DPRINTK("Bad number of segments in request (%d)\n", nseg);
+                /* Haven't submitted any bio's yet. */
+                goto fail_response;
+        }
+
+        preq.dev           = req->handle;
+        preq.sector_number = req->u.rw.sector_number;
+        preq.nr_sects      = 0;
+
+        pending_req->blkif     = blkif;
+        pending_req->id        = req->id;
+        pending_req->operation = req->operation;
+        pending_req->status    = BLKIF_RSP_OKAY;
+        pending_req->nr_pages  = nseg;
+
+        for (i = 0; i < nseg; i++) {
+                seg[i].nsec = req->u.rw.seg[i].last_sect -
+                        req->u.rw.seg[i].first_sect + 1;
+                if ((req->u.rw.seg[i].last_sect >= (PAGE_SIZE >> 9)) ||
+                    (req->u.rw.seg[i].last_sect < req->u.rw.seg[i].first_sect))
+                        goto fail_response;
+                preq.nr_sects += seg[i].nsec;
+
+        }
+
+        if (vbd_translate(&preq, blkif, operation) != 0) {
+                DPRINTK("access denied: %s of [%llu,%llu] on dev=%04x\n",
+                        operation == READ ? "read" : "write",
+                        preq.sector_number,
+                        preq.sector_number + preq.nr_sects, preq.dev);
+                goto fail_response;
+        }
+        /* This check _MUST_ be done after vbd_translate as the preq.bdev
+         * is set there. */
+        for (i = 0; i < nseg; i++) {
+                if (((int)preq.sector_number|(int)seg[i].nsec) &
+                    ((bdev_logical_block_size(preq.bdev) >> 9) - 1)) {
+                        DPRINTK("Misaligned I/O request from domain %d",
+                                blkif->domid);
+                        goto fail_response;
+                }
+        }
+        /* If we have failed at this point, we need to undo the M2P override,
+         * set gnttab_set_unmap_op on all of the grant references and perform
+         * the hypercall to unmap the grants - that is all done in
+         * xen_blkbk_unmap.
+         */
+        if (xen_blkbk_map(req, pending_req, seg))
+                goto fail_flush;
+
+        /* This corresponding blkif_put is done in __end_block_io_op */
+        blkif_get(blkif);
+
+        for (i = 0; i < nseg; i++) {
+                while ((bio == NULL) ||
+                       (bio_add_page(bio,
+                                     blkbk->pending_page(pending_req, i),
+                                     seg[i].nsec << 9,
+                                     seg[i].buf & ~PAGE_MASK) == 0)) {
+
+                        bio = biolist[nbio++] = bio_alloc(GFP_KERNEL, nseg-i);
+                        if (unlikely(bio == NULL))
+                                goto fail_put_bio;
+
+                        bio->bi_bdev    = preq.bdev;
+                        bio->bi_private = pending_req;
+                        bio->bi_end_io  = end_block_io_op;
+                        bio->bi_sector  = preq.sector_number;
+                }
+
+                preq.sector_number += seg[i].nsec;
+        }
+
+        /* This will be hit if the operation was a barrier. */
+        if (!bio) {
+                BUG_ON(operation != WRITE_BARRIER);
+                bio = biolist[nbio++] = bio_alloc(GFP_KERNEL, 0);
+                if (unlikely(bio == NULL))
+                        goto fail_put_bio;
+
+                bio->bi_bdev    = preq.bdev;
+                bio->bi_private = pending_req;
+                bio->bi_end_io  = end_block_io_op;
+                bio->bi_sector  = -1;
+        }
+
+
+        /* We set it one so that the last submit_bio does not have to call
+         * atomic_inc.
+         */
+        atomic_set(&pending_req->pendcnt, nbio);
+
+        /* Get a reference count for the disk queue and start sending I/O */
+        blk_start_plug(&plug);
+
+        for (i = 0; i < nbio; i++)
+                submit_bio(operation, biolist[i]);
+
+        blk_finish_plug(&plug);
+        /* Let the I/Os go.. */
+
+        if (operation == READ)
+                blkif->st_rd_sect += preq.nr_sects;
+        else if (operation == WRITE || operation == WRITE_BARRIER)
+                blkif->st_wr_sect += preq.nr_sects;
+
+        return;
+
+ fail_flush:
+        xen_blkbk_unmap(pending_req);
+ fail_response:
+        /* Haven't submitted any bio's yet. */
+        make_response(blkif, req->id, req->operation, BLKIF_RSP_ERROR);
+        free_req(pending_req);
+        msleep(1); /* back off a bit */
+        return;
+
+ fail_put_bio:
+        for (i = 0; i < (nbio-1); i++)
+                bio_put(biolist[i]);
+        __end_block_io_op(pending_req, -EINVAL);
+        msleep(1); /* back off a bit */
+        return;
+}
+
+
+
+/*
+ * Put a response on the ring on how the operation fared.
+ */
+static void make_response(struct blkif_st *blkif, u64 id,
+                          unsigned short op, int st)
+{
+        struct blkif_response  resp;
+        unsigned long     flags;
+        union blkif_back_rings *blk_rings = &blkif->blk_rings;
+        int more_to_do = 0;
+        int notify;
+
+        resp.id        = id;
+        resp.operation = op;
+        resp.status    = st;
+
+        spin_lock_irqsave(&blkif->blk_ring_lock, flags);
+        /* Place on the response ring for the relevant domain. */
+        switch (blkif->blk_protocol) {
+        case BLKIF_PROTOCOL_NATIVE:
+                memcpy(RING_GET_RESPONSE(&blk_rings->native, blk_rings->native.rsp_prod_pvt),
+                       &resp, sizeof(resp));
+                break;
+        case BLKIF_PROTOCOL_X86_32:
+                memcpy(RING_GET_RESPONSE(&blk_rings->x86_32, blk_rings->x86_32.rsp_prod_pvt),
+                       &resp, sizeof(resp));
+                break;
+        case BLKIF_PROTOCOL_X86_64:
+                memcpy(RING_GET_RESPONSE(&blk_rings->x86_64, blk_rings->x86_64.rsp_prod_pvt),
+                       &resp, sizeof(resp));
+                break;
+        default:
+                BUG();
+        }
+        blk_rings->common.rsp_prod_pvt++;
+        RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&blk_rings->common, notify);
+        if (blk_rings->common.rsp_prod_pvt == blk_rings->common.req_cons) {
+                /*
+                 * Tail check for pending requests. Allows frontend to avoid
+                 * notifications if requests are already in flight (lower
+                 * overheads and promotes batching).
+                 */
+                RING_FINAL_CHECK_FOR_REQUESTS(&blk_rings->common, more_to_do);
+
+        } else if (RING_HAS_UNCONSUMED_REQUESTS(&blk_rings->common)) {
+                more_to_do = 1;
+        }
+
+        spin_unlock_irqrestore(&blkif->blk_ring_lock, flags);
+
+        if (more_to_do)
+                blkif_notify_work(blkif);
+        if (notify)
+                notify_remote_via_irq(blkif->irq);
+}
+
+static int __init blkif_init(void)
+{
+        int i, mmap_pages;
+        int rc = 0;
+
+        if (!xen_pv_domain())
+                return -ENODEV;
+
+        blkbk = kzalloc(sizeof(struct xen_blkbk), GFP_KERNEL);
+        if (!blkbk) {
+                printk(KERN_ALERT "%s: out of memory!\n", __func__);
+                return -ENOMEM;
+        }
+
+        mmap_pages = blkif_reqs * BLKIF_MAX_SEGMENTS_PER_REQUEST;
+
+        blkbk->pending_reqs          = kmalloc(sizeof(blkbk->pending_reqs[0]) *
+                                        blkif_reqs, GFP_KERNEL);
+        blkbk->pending_grant_handles = kzalloc(sizeof(blkbk->pending_grant_handles[0]) *
+                                        mmap_pages, GFP_KERNEL);
+        blkbk->pending_pages         = kzalloc(sizeof(blkbk->pending_pages[0]) *
+                                        mmap_pages, GFP_KERNEL);
+
+        if (!blkbk->pending_reqs || !blkbk->pending_grant_handles ||
+            !blkbk->pending_pages) {
+                rc = -ENOMEM;
+                goto out_of_memory;
+        }
+
+        for (i = 0; i < mmap_pages; i++) {
+                blkbk->pending_grant_handles[i] = BLKBACK_INVALID_HANDLE;
+                blkbk->pending_pages[i] = alloc_page(GFP_KERNEL);
+                if (blkbk->pending_pages[i] == NULL) {
+                        rc = -ENOMEM;
+                        goto out_of_memory;
+                }
+        }
+        rc = blkif_interface_init();
+        if (rc)
+                goto failed_init;
+
+        memset(blkbk->pending_reqs, 0, sizeof(blkbk->pending_reqs));
+
+        INIT_LIST_HEAD(&blkbk->pending_free);
+        spin_lock_init(&blkbk->pending_free_lock);
+        init_waitqueue_head(&blkbk->pending_free_wq);
+
+        for (i = 0; i < blkif_reqs; i++)
+                list_add_tail(&blkbk->pending_reqs[i].free_list,
+                              &blkbk->pending_free);
+
+        rc = blkif_xenbus_init();
+        if (rc)
+                goto failed_init;
+
+        return 0;
+
+ out_of_memory:
+        printk(KERN_ERR "%s: out of memory\n", __func__);
+ failed_init:
+        kfree(blkbk->pending_reqs);
+        kfree(blkbk->pending_grant_handles);
+        for (i = 0; i < mmap_pages; i++) {
+                if (blkbk->pending_pages[i])
+                        __free_page(blkbk->pending_pages[i]);
+        }
+        kfree(blkbk->pending_pages);
+        kfree(blkbk);
+        blkbk = NULL;
+        return rc;
+}
+
+module_init(blkif_init);
+
+MODULE_LICENSE("Dual BSD/GPL");