blkback.c

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/******************************************************************************
 *
 * 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 <xen/xen.h>
#include <asm/xen/hypervisor.h>
#include <asm/xen/hypercall.h>
#include "common.h"

/*
 * 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 'xen_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 xen_blkif_reqs = 64;
module_param_named(reqs, xen_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;
module_param(log_stats, 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 xen_blkif    *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 xen_blkif *blkif);
static int dispatch_rw_block_io(struct xen_blkif *blkif,
                struct blkif_request *req,
                struct pending_req *pending_req);
static void make_response(struct xen_blkif *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);
}

/*
 * Routines for managing virtual block devices (vbds).
 */
static int xen_vbd_translate(struct phys_req *req, struct xen_blkif *blkif,
                 int operation)
{
    struct xen_vbd *vbd = &blkif->vbd;
    int rc = -EACCES;

    if ((operation != READ) && vbd->readonly)
        goto out;

    if (likely(req->nr_sects)) {
        blkif_sector_t end = req->sector_number + req->nr_sects;

        if (unlikely(end < req->sector_number))
            goto out;
        if (unlikely(end > vbd_sz(vbd)))
            goto out;
    }

    req->dev  = vbd->pdevice;
    req->bdev = vbd->bdev;
    rc = 0;

 out:
    return rc;
}

static void xen_vbd_resize(struct xen_blkif *blkif)
{
    struct xen_vbd *vbd = &blkif->vbd;
    struct xenbus_transaction xbt;
    int err;
    struct xenbus_device *dev = xen_blkbk_xenbus(blkif->be);
    unsigned long long new_size = vbd_sz(vbd);

    pr_info(DRV_PFX "VBD Resize: Domid: %d, Device: (%d, %d)\n",
        blkif->domid, MAJOR(vbd->pdevice), MINOR(vbd->pdevice));
    pr_info(DRV_PFX "VBD Resize: new size %llu\n", new_size);
    vbd->size = new_size;
again:
    err = xenbus_transaction_start(&xbt);
    if (err) {
        pr_warn(DRV_PFX "Error starting transaction");
        return;
    }
    err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu",
                (unsigned long long)vbd_sz(vbd));
    if (err) {
        pr_warn(DRV_PFX "Error writing new size");
        goto abort;
    }
    /*
     * Write the current state; we will use this to synchronize
     * the front-end. If the current state is "connected" the
     * front-end will get the new size information online.
     */
    err = xenbus_printf(xbt, dev->nodename, "state", "%d", dev->state);
    if (err) {
        pr_warn(DRV_PFX "Error writing the state");
        goto abort;
    }

    err = xenbus_transaction_end(xbt, 0);
    if (err == -EAGAIN)
        goto again;
    if (err)
        pr_warn(DRV_PFX "Error ending transaction");
    return;
abort:
    xenbus_transaction_end(xbt, 1);
}

/*
 * Notification from the guest OS.
 */
static void blkif_notify_work(struct xen_blkif *blkif)
{
    blkif->waiting_reqs = 1;
    wake_up(&blkif->wq);
}

irqreturn_t xen_blkif_be_int(int irq, void *dev_id)
{
    blkif_notify_work(dev_id);
    return IRQ_HANDLED;
}

/*
 * SCHEDULER FUNCTIONS
 */

static void print_stats(struct xen_blkif *blkif)
{
    pr_info("xen-blkback (%s): oo %3d  |  rd %4d  |  wr %4d  |  f %4d"
         "  |  ds %4d\n",
         current->comm, blkif->st_oo_req,
         blkif->st_rd_req, blkif->st_wr_req,
         blkif->st_f_req, blkif->st_ds_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;
    blkif->st_ds_req = 0;
}

int xen_blkif_schedule(void *arg)
{
    struct xen_blkif *blkif = arg;
    struct xen_vbd *vbd = &blkif->vbd;

    xen_blkif_get(blkif);

    while (!kthread_should_stop()) {
        if (try_to_freeze())
            continue;
        if (unlikely(vbd->size != vbd_sz(vbd)))
            xen_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);

    blkif->xenblkd = NULL;
    xen_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];
    struct page *pages[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;
        pages[invcount] = virt_to_page(vaddr(req, i));
        invcount++;
    }

    ret = gnttab_unmap_refs(unmap, NULL, pages, invcount);
    BUG_ON(ret);
}

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->u.rw.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 = gnttab_map_refs(map, NULL, &blkbk->pending_page(pending_req, 0), nseg);
    BUG_ON(ret);

    /*
     * Now swizzle 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)) {
            pr_debug(DRV_PFX "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;

        seg[i].buf  = map[i].dev_bus_addr |
            (req->u.rw.seg[i].first_sect << 9);
    }
    return ret;
}

static int dispatch_discard_io(struct xen_blkif *blkif,
                struct blkif_request *req)
{
    int err = 0;
    int status = BLKIF_RSP_OKAY;
    struct block_device *bdev = blkif->vbd.bdev;
    unsigned long secure;

    blkif->st_ds_req++;

    xen_blkif_get(blkif);
    secure = (blkif->vbd.discard_secure &&
         (req->u.discard.flag & BLKIF_DISCARD_SECURE)) ?
         BLKDEV_DISCARD_SECURE : 0;

    err = blkdev_issue_discard(bdev, req->u.discard.sector_number,
                   req->u.discard.nr_sectors,
                   GFP_KERNEL, secure);

    if (err == -EOPNOTSUPP) {
        pr_debug(DRV_PFX "discard op failed, not supported\n");
        status = BLKIF_RSP_EOPNOTSUPP;
    } else if (err)
        status = BLKIF_RSP_ERROR;

    make_response(blkif, req->u.discard.id, req->operation, status);
    xen_blkif_put(blkif);
    return err;
}

static void xen_blk_drain_io(struct xen_blkif *blkif)
{
    atomic_set(&blkif->drain, 1);
    do {
        /* The initial value is one, and one refcnt taken at the
         * start of the xen_blkif_schedule thread. */
        if (atomic_read(&blkif->refcnt) <= 2)
            break;
        wait_for_completion_interruptible_timeout(
                &blkif->drain_complete, HZ);

        if (!atomic_read(&blkif->drain))
            break;
    } while (!kthread_should_stop());
    atomic_set(&blkif->drain, 0);
}

/*
 * 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_FLUSH_DISKCACHE) &&
        (error == -EOPNOTSUPP)) {
        pr_debug(DRV_PFX "flush diskcache op failed, not supported\n");
        xen_blkbk_flush_diskcache(XBT_NIL, pending_req->blkif->be, 0);
        pending_req->status = BLKIF_RSP_EOPNOTSUPP;
    } else if ((pending_req->operation == BLKIF_OP_WRITE_BARRIER) &&
            (error == -EOPNOTSUPP)) {
        pr_debug(DRV_PFX "write barrier op failed, not supported\n");
        xen_blkbk_barrier(XBT_NIL, pending_req->blkif->be, 0);
        pending_req->status = BLKIF_RSP_EOPNOTSUPP;
    } else if (error) {
        pr_debug(DRV_PFX "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);
        xen_blkif_put(pending_req->blkif);
        if (atomic_read(&pending_req->blkif->refcnt) <= 2) {
            if (atomic_read(&pending_req->blkif->drain))
                complete(&pending_req->blkif->drain_complete);
        }
        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 xen_blkif *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();
        if (unlikely(req.operation == BLKIF_OP_DISCARD)) {
            free_req(pending_req);
            if (dispatch_discard_io(blkif, &req))
                break;
        } else if (dispatch_rw_block_io(blkif, &req, pending_req))
            break;

        /* Yield point for this unbounded loop. */
        cond_resched();
    }

    return more_to_do;
}

static int
do_block_io_op(struct xen_blkif *blkif)
{
    union blkif_back_rings *blk_rings = &blkif->blk_rings;
    int more_to_do;

    do {
        more_to_do = __do_block_io_op(blkif);
        if (more_to_do)
            break;

        RING_FINAL_CHECK_FOR_REQUESTS(&blk_rings->common, more_to_do);
    } while (more_to_do);

    return more_to_do;
}
/*
 * Transmutation of the 'struct blkif_request' to a proper 'struct bio'
 * and call the 'submit_bio' to pass it to the underlying storage.
 */
static int dispatch_rw_block_io(struct xen_blkif *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;
    bool drain = false;

    switch (req->operation) {
    case BLKIF_OP_READ:
        blkif->st_rd_req++;
        operation = READ;
        break;
    case BLKIF_OP_WRITE:
        blkif->st_wr_req++;
        operation = WRITE_ODIRECT;
        break;
    case BLKIF_OP_WRITE_BARRIER:
        drain = true;
    case BLKIF_OP_FLUSH_DISKCACHE:
        blkif->st_f_req++;
        operation = WRITE_FLUSH;
        break;
    default:
        operation = 0; /* make gcc happy */
        goto fail_response;
        break;
    }

    /* Check that the number of segments is sane. */
    nseg = req->u.rw.nr_segments;

    if (unlikely(nseg == 0 && operation != WRITE_FLUSH) ||
        unlikely(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
        pr_debug(DRV_PFX "Bad number of segments in request (%d)\n",
             nseg);
        /* Haven't submitted any bio's yet. */
        goto fail_response;
    }

    preq.dev           = req->u.rw.handle;
    preq.sector_number = req->u.rw.sector_number;
    preq.nr_sects      = 0;

    pending_req->blkif     = blkif;
    pending_req->id        = req->u.rw.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 (xen_vbd_translate(&preq, blkif, operation) != 0) {
        pr_debug(DRV_PFX "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 xen_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)) {
            pr_debug(DRV_PFX "Misaligned I/O request from domain %d",
                 blkif->domid);
            goto fail_response;
        }
    }

    /* Wait on all outstanding I/O's and once that has been completed
     * issue the WRITE_FLUSH.
     */
    if (drain)
        xen_blk_drain_io(pending_req->blkif);

    /*
     * 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 xen_blkif_put is done in __end_block_io_op, or
     * below (in "!bio") if we are handling a BLKIF_OP_DISCARD.
     */
    xen_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 = bio_alloc(GFP_KERNEL, nseg-i);
            if (unlikely(bio == NULL))
                goto fail_put_bio;

            biolist[nbio++] = 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 flush or discard. */
    if (!bio) {
        BUG_ON(operation != WRITE_FLUSH);

        bio = bio_alloc(GFP_KERNEL, 0);
        if (unlikely(bio == NULL))
            goto fail_put_bio;

        biolist[nbio++] = bio;
        bio->bi_bdev    = preq.bdev;
        bio->bi_private = pending_req;
        bio->bi_end_io  = end_block_io_op;
    }

    /*
     * 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]);

    /* Let the I/Os go.. */
    blk_finish_plug(&plug);

    if (operation == READ)
        blkif->st_rd_sect += preq.nr_sects;
    else if (operation & WRITE)
        blkif->st_wr_sect += preq.nr_sects;

    return 0;

 fail_flush:
    xen_blkbk_unmap(pending_req);
 fail_response:
    /* Haven't submitted any bio's yet. */
    make_response(blkif, req->u.rw.id, req->operation, BLKIF_RSP_ERROR);
    free_req(pending_req);
    msleep(1); /* back off a bit */
    return -EIO;

 fail_put_bio:
    for (i = 0; i < nbio; i++)
        bio_put(biolist[i]);
    __end_block_io_op(pending_req, -EINVAL);
    msleep(1); /* back off a bit */
    return -EIO;
}



/*
 * Put a response on the ring on how the operation fared.
 */
static void make_response(struct xen_blkif *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 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);
    spin_unlock_irqrestore(&blkif->blk_ring_lock, flags);
    if (notify)
        notify_remote_via_irq(blkif->irq);
}

static int __init xen_blkif_init(void)
{
    int i, mmap_pages;
    int rc = 0;

    if (!xen_domain())
        return -ENODEV;

    blkbk = kzalloc(sizeof(struct xen_blkbk), GFP_KERNEL);
    if (!blkbk) {
        pr_alert(DRV_PFX "%s: out of memory!\n", __func__);
        return -ENOMEM;
    }

    mmap_pages = xen_blkif_reqs * BLKIF_MAX_SEGMENTS_PER_REQUEST;

    blkbk->pending_reqs          = kzalloc(sizeof(blkbk->pending_reqs[0]) *
                    xen_blkif_reqs, GFP_KERNEL);
    blkbk->pending_grant_handles = kmalloc(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 = xen_blkif_interface_init();
    if (rc)
        goto failed_init;

    INIT_LIST_HEAD(&blkbk->pending_free);
    spin_lock_init(&blkbk->pending_free_lock);
    init_waitqueue_head(&blkbk->pending_free_wq);

    for (i = 0; i < xen_blkif_reqs; i++)
        list_add_tail(&blkbk->pending_reqs[i].free_list,
                  &blkbk->pending_free);

    rc = xen_blkif_xenbus_init();
    if (rc)
        goto failed_init;

    return 0;

 out_of_memory:
    pr_alert(DRV_PFX "%s: out of memory\n", __func__);
 failed_init:
    kfree(blkbk->pending_reqs);
    kfree(blkbk->pending_grant_handles);
    if (blkbk->pending_pages) {
        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(xen_blkif_init);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_ALIAS("xen-backend:vbd");