Count dirty blocks and expose an API to get dirty count

[qemu.git] / block.c

/*
 * QEMU System Emulator block driver
 *
 * Copyright (c) 2003 Fabrice Bellard
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (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 "config-host.h"
#include "qemu-common.h"
#include "monitor.h"
#include "block_int.h"
#include "module.h"
#include "qemu-objects.h"

#ifdef CONFIG_BSD
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/queue.h>
#ifndef __DragonFly__
#include <sys/disk.h>
#endif
#endif

#ifdef _WIN32
#include <windows.h>
#endif

static BlockDriverAIOCB *bdrv_aio_readv_em(BlockDriverState *bs,
        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
        BlockDriverCompletionFunc *cb, void *opaque);
static BlockDriverAIOCB *bdrv_aio_writev_em(BlockDriverState *bs,
        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
        BlockDriverCompletionFunc *cb, void *opaque);
static BlockDriverAIOCB *bdrv_aio_flush_em(BlockDriverState *bs,
        BlockDriverCompletionFunc *cb, void *opaque);
static int bdrv_read_em(BlockDriverState *bs, int64_t sector_num,
                        uint8_t *buf, int nb_sectors);
static int bdrv_write_em(BlockDriverState *bs, int64_t sector_num,
                         const uint8_t *buf, int nb_sectors);

BlockDriverState *bdrv_first;

static BlockDriver *first_drv;

/* If non-zero, use only whitelisted block drivers */
static int use_bdrv_whitelist;

int path_is_absolute(const char *path)
{
    const char *p;
#ifdef _WIN32
    /* specific case for names like: "\\.\d:" */
    if (*path == '/' || *path == '\\')
        return 1;
#endif
    p = strchr(path, ':');
    if (p)
        p++;
    else
        p = path;
#ifdef _WIN32
    return (*p == '/' || *p == '\\');
#else
    return (*p == '/');
#endif
}

/* if filename is absolute, just copy it to dest. Otherwise, build a
   path to it by considering it is relative to base_path. URL are
   supported. */
void path_combine(char *dest, int dest_size,
                  const char *base_path,
                  const char *filename)
{
    const char *p, *p1;
    int len;

    if (dest_size <= 0)
        return;
    if (path_is_absolute(filename)) {
        pstrcpy(dest, dest_size, filename);
    } else {
        p = strchr(base_path, ':');
        if (p)
            p++;
        else
            p = base_path;
        p1 = strrchr(base_path, '/');
#ifdef _WIN32
        {
            const char *p2;
            p2 = strrchr(base_path, '\\');
            if (!p1 || p2 > p1)
                p1 = p2;
        }
#endif
        if (p1)
            p1++;
        else
            p1 = base_path;
        if (p1 > p)
            p = p1;
        len = p - base_path;
        if (len > dest_size - 1)
            len = dest_size - 1;
        memcpy(dest, base_path, len);
        dest[len] = '\0';
        pstrcat(dest, dest_size, filename);
    }
}

void bdrv_register(BlockDriver *bdrv)
{
    if (!bdrv->bdrv_aio_readv) {
        /* add AIO emulation layer */
        bdrv->bdrv_aio_readv = bdrv_aio_readv_em;
        bdrv->bdrv_aio_writev = bdrv_aio_writev_em;
    } else if (!bdrv->bdrv_read) {
        /* add synchronous IO emulation layer */
        bdrv->bdrv_read = bdrv_read_em;
        bdrv->bdrv_write = bdrv_write_em;
    }

    if (!bdrv->bdrv_aio_flush)
        bdrv->bdrv_aio_flush = bdrv_aio_flush_em;

    bdrv->next = first_drv;
    first_drv = bdrv;
}

/* create a new block device (by default it is empty) */
BlockDriverState *bdrv_new(const char *device_name)
{
    BlockDriverState **pbs, *bs;

    bs = qemu_mallocz(sizeof(BlockDriverState));
    pstrcpy(bs->device_name, sizeof(bs->device_name), device_name);
    if (device_name[0] != '\0') {
        /* insert at the end */
        pbs = &bdrv_first;
        while (*pbs != NULL)
            pbs = &(*pbs)->next;
        *pbs = bs;
    }
    return bs;
}

BlockDriver *bdrv_find_format(const char *format_name)
{
    BlockDriver *drv1;
    for(drv1 = first_drv; drv1 != NULL; drv1 = drv1->next) {
        if (!strcmp(drv1->format_name, format_name))
            return drv1;
    }
    return NULL;
}

static int bdrv_is_whitelisted(BlockDriver *drv)
{
    static const char *whitelist[] = {
        CONFIG_BDRV_WHITELIST
    };
    const char **p;

    if (!whitelist[0])
        return 1;               /* no whitelist, anything goes */

    for (p = whitelist; *p; p++) {
        if (!strcmp(drv->format_name, *p)) {
            return 1;
        }
    }
    return 0;
}

BlockDriver *bdrv_find_whitelisted_format(const char *format_name)
{
    BlockDriver *drv = bdrv_find_format(format_name);
    return drv && bdrv_is_whitelisted(drv) ? drv : NULL;
}

int bdrv_create(BlockDriver *drv, const char* filename,
    QEMUOptionParameter *options)
{
    if (!drv->bdrv_create)
        return -ENOTSUP;

    return drv->bdrv_create(filename, options);
}

#ifdef _WIN32
void get_tmp_filename(char *filename, int size)
{
    char temp_dir[MAX_PATH];

    GetTempPath(MAX_PATH, temp_dir);
    GetTempFileName(temp_dir, "qem", 0, filename);
}
#else
void get_tmp_filename(char *filename, int size)
{
    int fd;
    const char *tmpdir;
    /* XXX: race condition possible */
    tmpdir = getenv("TMPDIR");
    if (!tmpdir)
        tmpdir = "/tmp";
    snprintf(filename, size, "%s/vl.XXXXXX", tmpdir);
    fd = mkstemp(filename);
    close(fd);
}
#endif

#ifdef _WIN32
static int is_windows_drive_prefix(const char *filename)
{
    return (((filename[0] >= 'a' && filename[0] <= 'z') ||
             (filename[0] >= 'A' && filename[0] <= 'Z')) &&
            filename[1] == ':');
}

int is_windows_drive(const char *filename)
{
    if (is_windows_drive_prefix(filename) &&
        filename[2] == '\0')
        return 1;
    if (strstart(filename, "\\\\.\\", NULL) ||
        strstart(filename, "//./", NULL))
        return 1;
    return 0;
}
#endif

static BlockDriver *find_protocol(const char *filename)
{
    BlockDriver *drv1;
    char protocol[128];
    int len;
    const char *p;

#ifdef _WIN32
    if (is_windows_drive(filename) ||
        is_windows_drive_prefix(filename))
        return bdrv_find_format("raw");
#endif
    p = strchr(filename, ':');
    if (!p)
        return bdrv_find_format("raw");
    len = p - filename;
    if (len > sizeof(protocol) - 1)
        len = sizeof(protocol) - 1;
    memcpy(protocol, filename, len);
    protocol[len] = '\0';
    for(drv1 = first_drv; drv1 != NULL; drv1 = drv1->next) {
        if (drv1->protocol_name &&
            !strcmp(drv1->protocol_name, protocol))
            return drv1;
    }
    return NULL;
}

/*
 * Detect host devices. By convention, /dev/cdrom[N] is always
 * recognized as a host CDROM.
 */
static BlockDriver *find_hdev_driver(const char *filename)
{
    int score_max = 0, score;
    BlockDriver *drv = NULL, *d;

    for (d = first_drv; d; d = d->next) {
        if (d->bdrv_probe_device) {
            score = d->bdrv_probe_device(filename);
            if (score > score_max) {
                score_max = score;
                drv = d;
            }
        }
    }

    return drv;
}

static BlockDriver *find_image_format(const char *filename)
{
    int ret, score, score_max;
    BlockDriver *drv1, *drv;
    uint8_t buf[2048];
    BlockDriverState *bs;

    drv = find_protocol(filename);
    /* no need to test disk image formats for vvfat */
    if (drv && strcmp(drv->format_name, "vvfat") == 0)
        return drv;

    ret = bdrv_file_open(&bs, filename, 0);
    if (ret < 0)
        return NULL;
    ret = bdrv_pread(bs, 0, buf, sizeof(buf));
    bdrv_delete(bs);
    if (ret < 0) {
        return NULL;
    }

    score_max = 0;
    for(drv1 = first_drv; drv1 != NULL; drv1 = drv1->next) {
        if (drv1->bdrv_probe) {
            score = drv1->bdrv_probe(buf, ret, filename);
            if (score > score_max) {
                score_max = score;
                drv = drv1;
            }
        }
    }
    return drv;
}

int bdrv_file_open(BlockDriverState **pbs, const char *filename, int flags)
{
    BlockDriverState *bs;
    int ret;

    bs = bdrv_new("");
    ret = bdrv_open2(bs, filename, flags | BDRV_O_FILE, NULL);
    if (ret < 0) {
        bdrv_delete(bs);
        return ret;
    }
    bs->growable = 1;
    *pbs = bs;
    return 0;
}

int bdrv_open(BlockDriverState *bs, const char *filename, int flags)
{
    return bdrv_open2(bs, filename, flags, NULL);
}

int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
               BlockDriver *drv)
{
    int ret, open_flags;
    char tmp_filename[PATH_MAX];
    char backing_filename[PATH_MAX];

    bs->is_temporary = 0;
    bs->encrypted = 0;
    bs->valid_key = 0;
    /* buffer_alignment defaulted to 512, drivers can change this value */
    bs->buffer_alignment = 512;

    if (flags & BDRV_O_SNAPSHOT) {
        BlockDriverState *bs1;
        int64_t total_size;
        int is_protocol = 0;
        BlockDriver *bdrv_qcow2;
        QEMUOptionParameter *options;

        /* if snapshot, we create a temporary backing file and open it
           instead of opening 'filename' directly */

        /* if there is a backing file, use it */
        bs1 = bdrv_new("");
        ret = bdrv_open2(bs1, filename, 0, drv);
        if (ret < 0) {
            bdrv_delete(bs1);
            return ret;
        }
        total_size = bdrv_getlength(bs1) >> BDRV_SECTOR_BITS;

        if (bs1->drv && bs1->drv->protocol_name)
            is_protocol = 1;

        bdrv_delete(bs1);

        get_tmp_filename(tmp_filename, sizeof(tmp_filename));

        /* Real path is meaningless for protocols */
        if (is_protocol)
            snprintf(backing_filename, sizeof(backing_filename),
                     "%s", filename);
        else if (!realpath(filename, backing_filename))
            return -errno;

        bdrv_qcow2 = bdrv_find_format("qcow2");
        options = parse_option_parameters("", bdrv_qcow2->create_options, NULL);

        set_option_parameter_int(options, BLOCK_OPT_SIZE, total_size * 512);
        set_option_parameter(options, BLOCK_OPT_BACKING_FILE, backing_filename);
        if (drv) {
            set_option_parameter(options, BLOCK_OPT_BACKING_FMT,
                drv->format_name);
        }

        ret = bdrv_create(bdrv_qcow2, tmp_filename, options);
        if (ret < 0) {
            return ret;
        }

        filename = tmp_filename;
        drv = bdrv_qcow2;
        bs->is_temporary = 1;
    }

    pstrcpy(bs->filename, sizeof(bs->filename), filename);
    if (flags & BDRV_O_FILE) {
        drv = find_protocol(filename);
    } else if (!drv) {
        drv = find_hdev_driver(filename);
        if (!drv) {
            drv = find_image_format(filename);
        }
    }

    if (!drv) {
        ret = -ENOENT;
        goto unlink_and_fail;
    }
    if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv)) {
        ret = -ENOTSUP;
        goto unlink_and_fail;
    }

    bs->drv = drv;
    bs->opaque = qemu_mallocz(drv->instance_size);

    /*
     * Yes, BDRV_O_NOCACHE aka O_DIRECT means we have to present a
     * write cache to the guest.  We do need the fdatasync to flush
     * out transactions for block allocations, and we maybe have a
     * volatile write cache in our backing device to deal with.
     */
    if (flags & (BDRV_O_CACHE_WB|BDRV_O_NOCACHE))
        bs->enable_write_cache = 1;

    bs->read_only = (flags & BDRV_O_RDWR) == 0;
    if (!(flags & BDRV_O_FILE)) {
        open_flags = (flags & (BDRV_O_RDWR | BDRV_O_CACHE_MASK|BDRV_O_NATIVE_AIO));
        if (bs->is_temporary) { /* snapshot should be writeable */
            open_flags |= BDRV_O_RDWR;
        }
    } else {
        open_flags = flags & ~(BDRV_O_FILE | BDRV_O_SNAPSHOT);
    }

    ret = drv->bdrv_open(bs, filename, open_flags);
    if (ret < 0) {
        goto free_and_fail;
    }

    if (drv->bdrv_getlength) {
        bs->total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
    }
#ifndef _WIN32
    if (bs->is_temporary) {
        unlink(filename);
    }
#endif
    if ((flags & BDRV_O_NO_BACKING) == 0 && bs->backing_file[0] != '\0') {
        /* if there is a backing file, use it */
        BlockDriver *back_drv = NULL;
        bs->backing_hd = bdrv_new("");
        path_combine(backing_filename, sizeof(backing_filename),
                     filename, bs->backing_file);
        if (bs->backing_format[0] != '\0')
            back_drv = bdrv_find_format(bs->backing_format);
        ret = bdrv_open2(bs->backing_hd, backing_filename, open_flags,
                         back_drv);
        bs->backing_hd->read_only =  (open_flags & BDRV_O_RDWR) == 0;
        if (ret < 0) {
            bdrv_close(bs);
            return ret;
        }
    }

    if (!bdrv_key_required(bs)) {
        /* call the change callback */
        bs->media_changed = 1;
        if (bs->change_cb)
            bs->change_cb(bs->change_opaque);
    }
    return 0;

free_and_fail:
    qemu_free(bs->opaque);
    bs->opaque = NULL;
    bs->drv = NULL;
unlink_and_fail:
    if (bs->is_temporary)
        unlink(filename);
    return ret;
}

void bdrv_close(BlockDriverState *bs)
{
    if (bs->drv) {
        if (bs->backing_hd)
            bdrv_delete(bs->backing_hd);
        bs->drv->bdrv_close(bs);
        qemu_free(bs->opaque);
#ifdef _WIN32
        if (bs->is_temporary) {
            unlink(bs->filename);
        }
#endif
        bs->opaque = NULL;
        bs->drv = NULL;

        /* call the change callback */
        bs->media_changed = 1;
        if (bs->change_cb)
            bs->change_cb(bs->change_opaque);
    }
}

void bdrv_delete(BlockDriverState *bs)
{
    BlockDriverState **pbs;

    pbs = &bdrv_first;
    while (*pbs != bs && *pbs != NULL)
        pbs = &(*pbs)->next;
    if (*pbs == bs)
        *pbs = bs->next;

    bdrv_close(bs);
    qemu_free(bs);
}

/*
 * Run consistency checks on an image
 *
 * Returns the number of errors or -errno when an internal error occurs
 */
int bdrv_check(BlockDriverState *bs)
{
    if (bs->drv->bdrv_check == NULL) {
        return -ENOTSUP;
    }

    return bs->drv->bdrv_check(bs);
}

/* commit COW file into the raw image */
int bdrv_commit(BlockDriverState *bs)
{
    BlockDriver *drv = bs->drv;
    int64_t i, total_sectors;
    int n, j;
    int ret = 0;
    unsigned char sector[512];

    if (!drv)
        return -ENOMEDIUM;

    if (bs->read_only) {
        return -EACCES;
    }

    if (!bs->backing_hd) {
        return -ENOTSUP;
    }

    total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
    for (i = 0; i < total_sectors;) {
        if (drv->bdrv_is_allocated(bs, i, 65536, &n)) {
            for(j = 0; j < n; j++) {
                if (bdrv_read(bs, i, sector, 1) != 0) {
                    return -EIO;
                }

                if (bdrv_write(bs->backing_hd, i, sector, 1) != 0) {
                    return -EIO;
                }
                i++;
            }
        } else {
            i += n;
        }
    }

    if (drv->bdrv_make_empty) {
        ret = drv->bdrv_make_empty(bs);
        bdrv_flush(bs);
    }

    /*
     * Make sure all data we wrote to the backing device is actually
     * stable on disk.
     */
    if (bs->backing_hd)
        bdrv_flush(bs->backing_hd);
    return ret;
}

/*
 * Return values:
 * 0        - success
 * -EINVAL  - backing format specified, but no file
 * -ENOSPC  - can't update the backing file because no space is left in the
 *            image file header
 * -ENOTSUP - format driver doesn't support changing the backing file
 */
int bdrv_change_backing_file(BlockDriverState *bs,
    const char *backing_file, const char *backing_fmt)
{
    BlockDriver *drv = bs->drv;

    if (drv->bdrv_change_backing_file != NULL) {
        return drv->bdrv_change_backing_file(bs, backing_file, backing_fmt);
    } else {
        return -ENOTSUP;
    }
}

static int bdrv_check_byte_request(BlockDriverState *bs, int64_t offset,
                                   size_t size)
{
    int64_t len;

    if (!bdrv_is_inserted(bs))
        return -ENOMEDIUM;

    if (bs->growable)
        return 0;

    len = bdrv_getlength(bs);

    if (offset < 0)
        return -EIO;

    if ((offset > len) || (len - offset < size))
        return -EIO;

    return 0;
}

static int bdrv_check_request(BlockDriverState *bs, int64_t sector_num,
                              int nb_sectors)
{
    return bdrv_check_byte_request(bs, sector_num * 512, nb_sectors * 512);
}

/* return < 0 if error. See bdrv_write() for the return codes */
int bdrv_read(BlockDriverState *bs, int64_t sector_num,
              uint8_t *buf, int nb_sectors)
{
    BlockDriver *drv = bs->drv;

    if (!drv)
        return -ENOMEDIUM;
    if (bdrv_check_request(bs, sector_num, nb_sectors))
        return -EIO;

    return drv->bdrv_read(bs, sector_num, buf, nb_sectors);
}

static void set_dirty_bitmap(BlockDriverState *bs, int64_t sector_num,
                             int nb_sectors, int dirty)
{
    int64_t start, end;
    unsigned long val, idx, bit;

    start = sector_num / BDRV_SECTORS_PER_DIRTY_CHUNK;
    end = (sector_num + nb_sectors - 1) / BDRV_SECTORS_PER_DIRTY_CHUNK;

    for (; start <= end; start++) {
        idx = start / (sizeof(unsigned long) * 8);
        bit = start % (sizeof(unsigned long) * 8);
        val = bs->dirty_bitmap[idx];
        if (dirty) {
            if (!(val & (1 << bit))) {
                bs->dirty_count++;
                val |= 1 << bit;
            }
        } else {
            if (val & (1 << bit)) {
                bs->dirty_count--;
                val &= ~(1 << bit);
            }
        }
        bs->dirty_bitmap[idx] = val;
    }
}

/* Return < 0 if error. Important errors are:
  -EIO         generic I/O error (may happen for all errors)
  -ENOMEDIUM   No media inserted.
  -EINVAL      Invalid sector number or nb_sectors
  -EACCES      Trying to write a read-only device
*/
int bdrv_write(BlockDriverState *bs, int64_t sector_num,
               const uint8_t *buf, int nb_sectors)
{
    BlockDriver *drv = bs->drv;
    if (!bs->drv)
        return -ENOMEDIUM;
    if (bs->read_only)
        return -EACCES;
    if (bdrv_check_request(bs, sector_num, nb_sectors))
        return -EIO;

    if (bs->dirty_bitmap) {
        set_dirty_bitmap(bs, sector_num, nb_sectors, 1);
    }

    return drv->bdrv_write(bs, sector_num, buf, nb_sectors);
}

int bdrv_pread(BlockDriverState *bs, int64_t offset,
               void *buf, int count1)
{
    uint8_t tmp_buf[BDRV_SECTOR_SIZE];
    int len, nb_sectors, count;
    int64_t sector_num;
    int ret;

    count = count1;
    /* first read to align to sector start */
    len = (BDRV_SECTOR_SIZE - offset) & (BDRV_SECTOR_SIZE - 1);
    if (len > count)
        len = count;
    sector_num = offset >> BDRV_SECTOR_BITS;
    if (len > 0) {
        if ((ret = bdrv_read(bs, sector_num, tmp_buf, 1)) < 0)
            return ret;
        memcpy(buf, tmp_buf + (offset & (BDRV_SECTOR_SIZE - 1)), len);
        count -= len;
        if (count == 0)
            return count1;
        sector_num++;
        buf += len;
    }

    /* read the sectors "in place" */
    nb_sectors = count >> BDRV_SECTOR_BITS;
    if (nb_sectors > 0) {
        if ((ret = bdrv_read(bs, sector_num, buf, nb_sectors)) < 0)
            return ret;
        sector_num += nb_sectors;
        len = nb_sectors << BDRV_SECTOR_BITS;
        buf += len;
        count -= len;
    }

    /* add data from the last sector */
    if (count > 0) {
        if ((ret = bdrv_read(bs, sector_num, tmp_buf, 1)) < 0)
            return ret;
        memcpy(buf, tmp_buf, count);
    }
    return count1;
}

int bdrv_pwrite(BlockDriverState *bs, int64_t offset,
                const void *buf, int count1)
{
    uint8_t tmp_buf[BDRV_SECTOR_SIZE];
    int len, nb_sectors, count;
    int64_t sector_num;
    int ret;

    count = count1;
    /* first write to align to sector start */
    len = (BDRV_SECTOR_SIZE - offset) & (BDRV_SECTOR_SIZE - 1);
    if (len > count)
        len = count;
    sector_num = offset >> BDRV_SECTOR_BITS;
    if (len > 0) {
        if ((ret = bdrv_read(bs, sector_num, tmp_buf, 1)) < 0)
            return ret;
        memcpy(tmp_buf + (offset & (BDRV_SECTOR_SIZE - 1)), buf, len);
        if ((ret = bdrv_write(bs, sector_num, tmp_buf, 1)) < 0)
            return ret;
        count -= len;
        if (count == 0)
            return count1;
        sector_num++;
        buf += len;
    }

    /* write the sectors "in place" */
    nb_sectors = count >> BDRV_SECTOR_BITS;
    if (nb_sectors > 0) {
        if ((ret = bdrv_write(bs, sector_num, buf, nb_sectors)) < 0)
            return ret;
        sector_num += nb_sectors;
        len = nb_sectors << BDRV_SECTOR_BITS;
        buf += len;
        count -= len;
    }

    /* add data from the last sector */
    if (count > 0) {
        if ((ret = bdrv_read(bs, sector_num, tmp_buf, 1)) < 0)
            return ret;
        memcpy(tmp_buf, buf, count);
        if ((ret = bdrv_write(bs, sector_num, tmp_buf, 1)) < 0)
            return ret;
    }
    return count1;
}

/**
 * Truncate file to 'offset' bytes (needed only for file protocols)
 */
int bdrv_truncate(BlockDriverState *bs, int64_t offset)
{
    BlockDriver *drv = bs->drv;
    if (!drv)
        return -ENOMEDIUM;
    if (!drv->bdrv_truncate)
        return -ENOTSUP;
    if (bs->read_only)
        return -EACCES;
    return drv->bdrv_truncate(bs, offset);
}

/**
 * Length of a file in bytes. Return < 0 if error or unknown.
 */
int64_t bdrv_getlength(BlockDriverState *bs)
{
    BlockDriver *drv = bs->drv;
    if (!drv)
        return -ENOMEDIUM;
    if (!drv->bdrv_getlength) {
        /* legacy mode */
        return bs->total_sectors * BDRV_SECTOR_SIZE;
    }
    return drv->bdrv_getlength(bs);
}

/* return 0 as number of sectors if no device present or error */
void bdrv_get_geometry(BlockDriverState *bs, uint64_t *nb_sectors_ptr)
{
    int64_t length;
    length = bdrv_getlength(bs);
    if (length < 0)
        length = 0;
    else
        length = length >> BDRV_SECTOR_BITS;
    *nb_sectors_ptr = length;
}

struct partition {
        uint8_t boot_ind;           /* 0x80 - active */
        uint8_t head;               /* starting head */
        uint8_t sector;             /* starting sector */
        uint8_t cyl;                /* starting cylinder */
        uint8_t sys_ind;            /* What partition type */
        uint8_t end_head;           /* end head */
        uint8_t end_sector;         /* end sector */
        uint8_t end_cyl;            /* end cylinder */
        uint32_t start_sect;        /* starting sector counting from 0 */
        uint32_t nr_sects;          /* nr of sectors in partition */
} __attribute__((packed));

/* try to guess the disk logical geometry from the MSDOS partition table. Return 0 if OK, -1 if could not guess */
static int guess_disk_lchs(BlockDriverState *bs,
                           int *pcylinders, int *pheads, int *psectors)
{
    uint8_t buf[512];
    int ret, i, heads, sectors, cylinders;
    struct partition *p;
    uint32_t nr_sects;
    uint64_t nb_sectors;

    bdrv_get_geometry(bs, &nb_sectors);

    ret = bdrv_read(bs, 0, buf, 1);
    if (ret < 0)
        return -1;
    /* test msdos magic */
    if (buf[510] != 0x55 || buf[511] != 0xaa)
        return -1;
    for(i = 0; i < 4; i++) {
        p = ((struct partition *)(buf + 0x1be)) + i;
        nr_sects = le32_to_cpu(p->nr_sects);
        if (nr_sects && p->end_head) {
            /* We make the assumption that the partition terminates on
               a cylinder boundary */
            heads = p->end_head + 1;
            sectors = p->end_sector & 63;
            if (sectors == 0)
                continue;
            cylinders = nb_sectors / (heads * sectors);
            if (cylinders < 1 || cylinders > 16383)
                continue;
            *pheads = heads;
            *psectors = sectors;
            *pcylinders = cylinders;
#if 0
            printf("guessed geometry: LCHS=%d %d %d\n",
                   cylinders, heads, sectors);
#endif
            return 0;
        }
    }
    return -1;
}

void bdrv_guess_geometry(BlockDriverState *bs, int *pcyls, int *pheads, int *psecs)
{
    int translation, lba_detected = 0;
    int cylinders, heads, secs;
    uint64_t nb_sectors;

    /* if a geometry hint is available, use it */
    bdrv_get_geometry(bs, &nb_sectors);
    bdrv_get_geometry_hint(bs, &cylinders, &heads, &secs);
    translation = bdrv_get_translation_hint(bs);
    if (cylinders != 0) {
        *pcyls = cylinders;
        *pheads = heads;
        *psecs = secs;
    } else {
        if (guess_disk_lchs(bs, &cylinders, &heads, &secs) == 0) {
            if (heads > 16) {
                /* if heads > 16, it means that a BIOS LBA
                   translation was active, so the default
                   hardware geometry is OK */
                lba_detected = 1;
                goto default_geometry;
            } else {
                *pcyls = cylinders;
                *pheads = heads;
                *psecs = secs;
                /* disable any translation to be in sync with
                   the logical geometry */
                if (translation == BIOS_ATA_TRANSLATION_AUTO) {
                    bdrv_set_translation_hint(bs,
                                              BIOS_ATA_TRANSLATION_NONE);
                }
            }
        } else {
        default_geometry:
            /* if no geometry, use a standard physical disk geometry */
            cylinders = nb_sectors / (16 * 63);

            if (cylinders > 16383)
                cylinders = 16383;
            else if (cylinders < 2)
                cylinders = 2;
            *pcyls = cylinders;
            *pheads = 16;
            *psecs = 63;
            if ((lba_detected == 1) && (translation == BIOS_ATA_TRANSLATION_AUTO)) {
                if ((*pcyls * *pheads) <= 131072) {
                    bdrv_set_translation_hint(bs,
                                              BIOS_ATA_TRANSLATION_LARGE);
                } else {
                    bdrv_set_translation_hint(bs,
                                              BIOS_ATA_TRANSLATION_LBA);
                }
            }
        }
        bdrv_set_geometry_hint(bs, *pcyls, *pheads, *psecs);
    }
}

void bdrv_set_geometry_hint(BlockDriverState *bs,
                            int cyls, int heads, int secs)
{
    bs->cyls = cyls;
    bs->heads = heads;
    bs->secs = secs;
}

void bdrv_set_type_hint(BlockDriverState *bs, int type)
{
    bs->type = type;
    bs->removable = ((type == BDRV_TYPE_CDROM ||
                      type == BDRV_TYPE_FLOPPY));
}

void bdrv_set_translation_hint(BlockDriverState *bs, int translation)
{
    bs->translation = translation;
}

void bdrv_get_geometry_hint(BlockDriverState *bs,
                            int *pcyls, int *pheads, int *psecs)
{
    *pcyls = bs->cyls;
    *pheads = bs->heads;
    *psecs = bs->secs;
}

int bdrv_get_type_hint(BlockDriverState *bs)
{
    return bs->type;
}

int bdrv_get_translation_hint(BlockDriverState *bs)
{
    return bs->translation;
}

int bdrv_is_removable(BlockDriverState *bs)
{
    return bs->removable;
}

int bdrv_is_read_only(BlockDriverState *bs)
{
    return bs->read_only;
}

int bdrv_is_sg(BlockDriverState *bs)
{
    return bs->sg;
}

int bdrv_enable_write_cache(BlockDriverState *bs)
{
    return bs->enable_write_cache;
}

/* XXX: no longer used */
void bdrv_set_change_cb(BlockDriverState *bs,
                        void (*change_cb)(void *opaque), void *opaque)
{
    bs->change_cb = change_cb;
    bs->change_opaque = opaque;
}

int bdrv_is_encrypted(BlockDriverState *bs)
{
    if (bs->backing_hd && bs->backing_hd->encrypted)
        return 1;
    return bs->encrypted;
}

int bdrv_key_required(BlockDriverState *bs)
{
    BlockDriverState *backing_hd = bs->backing_hd;

    if (backing_hd && backing_hd->encrypted && !backing_hd->valid_key)
        return 1;
    return (bs->encrypted && !bs->valid_key);
}

int bdrv_set_key(BlockDriverState *bs, const char *key)
{
    int ret;
    if (bs->backing_hd && bs->backing_hd->encrypted) {
        ret = bdrv_set_key(bs->backing_hd, key);
        if (ret < 0)
            return ret;
        if (!bs->encrypted)
            return 0;
    }
    if (!bs->encrypted || !bs->drv || !bs->drv->bdrv_set_key)
        return -1;
    ret = bs->drv->bdrv_set_key(bs, key);
    if (ret < 0) {
        bs->valid_key = 0;
    } else if (!bs->valid_key) {
        bs->valid_key = 1;
        /* call the change callback now, we skipped it on open */
        bs->media_changed = 1;
        if (bs->change_cb)
            bs->change_cb(bs->change_opaque);
    }
    return ret;
}

void bdrv_get_format(BlockDriverState *bs, char *buf, int buf_size)
{
    if (!bs->drv) {
        buf[0] = '\0';
    } else {
        pstrcpy(buf, buf_size, bs->drv->format_name);
    }
}

void bdrv_iterate_format(void (*it)(void *opaque, const char *name),
                         void *opaque)
{
    BlockDriver *drv;

    for (drv = first_drv; drv != NULL; drv = drv->next) {
        it(opaque, drv->format_name);
    }
}

BlockDriverState *bdrv_find(const char *name)
{
    BlockDriverState *bs;

    for (bs = bdrv_first; bs != NULL; bs = bs->next) {
        if (!strcmp(name, bs->device_name))
            return bs;
    }
    return NULL;
}

void bdrv_iterate(void (*it)(void *opaque, BlockDriverState *bs), void *opaque)
{
    BlockDriverState *bs;

    for (bs = bdrv_first; bs != NULL; bs = bs->next) {
        it(opaque, bs);
    }
}

const char *bdrv_get_device_name(BlockDriverState *bs)
{
    return bs->device_name;
}

void bdrv_flush(BlockDriverState *bs)
{
    if (bs->drv && bs->drv->bdrv_flush)
        bs->drv->bdrv_flush(bs);
}

void bdrv_flush_all(void)
{
    BlockDriverState *bs;

    for (bs = bdrv_first; bs != NULL; bs = bs->next)
        if (bs->drv && !bdrv_is_read_only(bs) && 
            (!bdrv_is_removable(bs) || bdrv_is_inserted(bs)))
            bdrv_flush(bs);
}

/*
 * Returns true iff the specified sector is present in the disk image. Drivers
 * not implementing the functionality are assumed to not support backing files,
 * hence all their sectors are reported as allocated.
 *
 * 'pnum' is set to the number of sectors (including and immediately following
 * the specified sector) that are known to be in the same
 * allocated/unallocated state.
 *
 * 'nb_sectors' is the max value 'pnum' should be set to.
 */
int bdrv_is_allocated(BlockDriverState *bs, int64_t sector_num, int nb_sectors,
        int *pnum)
{
    int64_t n;
    if (!bs->drv->bdrv_is_allocated) {
        if (sector_num >= bs->total_sectors) {
            *pnum = 0;
            return 0;
        }
        n = bs->total_sectors - sector_num;
        *pnum = (n < nb_sectors) ? (n) : (nb_sectors);
        return 1;
    }
    return bs->drv->bdrv_is_allocated(bs, sector_num, nb_sectors, pnum);
}

static void bdrv_print_dict(QObject *obj, void *opaque)
{
    QDict *bs_dict;
    Monitor *mon = opaque;

    bs_dict = qobject_to_qdict(obj);

    monitor_printf(mon, "%s: type=%s removable=%d",
                        qdict_get_str(bs_dict, "device"),
                        qdict_get_str(bs_dict, "type"),
                        qdict_get_bool(bs_dict, "removable"));

    if (qdict_get_bool(bs_dict, "removable")) {
        monitor_printf(mon, " locked=%d", qdict_get_bool(bs_dict, "locked"));
    }

    if (qdict_haskey(bs_dict, "inserted")) {
        QDict *qdict = qobject_to_qdict(qdict_get(bs_dict, "inserted"));

        monitor_printf(mon, " file=");
        monitor_print_filename(mon, qdict_get_str(qdict, "file"));
        if (qdict_haskey(qdict, "backing_file")) {
            monitor_printf(mon, " backing_file=");
            monitor_print_filename(mon, qdict_get_str(qdict, "backing_file"));
        }
        monitor_printf(mon, " ro=%d drv=%s encrypted=%d",
                            qdict_get_bool(qdict, "ro"),
                            qdict_get_str(qdict, "drv"),
                            qdict_get_bool(qdict, "encrypted"));
    } else {
        monitor_printf(mon, " [not inserted]");
    }

    monitor_printf(mon, "\n");
}

void bdrv_info_print(Monitor *mon, const QObject *data)
{
    qlist_iter(qobject_to_qlist(data), bdrv_print_dict, mon);
}

/**
 * bdrv_info(): Block devices information
 *
 * Each block device information is stored in a QDict and the
 * returned QObject is a QList of all devices.
 *
 * The QDict contains the following:
 *
 * - "device": device name
 * - "type": device type
 * - "removable": true if the device is removable, false otherwise
 * - "locked": true if the device is locked, false otherwise
 * - "inserted": only present if the device is inserted, it is a QDict
 *    containing the following:
 *          - "file": device file name
 *          - "ro": true if read-only, false otherwise
 *          - "drv": driver format name
 *          - "backing_file": backing file name if one is used
 *          - "encrypted": true if encrypted, false otherwise
 *
 * Example:
 *
 * [ { "device": "ide0-hd0", "type": "hd", "removable": false, "locked": false,
 *     "inserted": { "file": "/tmp/foobar", "ro": false, "drv": "qcow2" } },
 *   { "device": "floppy0", "type": "floppy", "removable": true,
 *     "locked": false } ]
 */
void bdrv_info(Monitor *mon, QObject **ret_data)
{
    QList *bs_list;
    BlockDriverState *bs;

    bs_list = qlist_new();

    for (bs = bdrv_first; bs != NULL; bs = bs->next) {
        QObject *bs_obj;
        const char *type = "unknown";

        switch(bs->type) {
        case BDRV_TYPE_HD:
            type = "hd";
            break;
        case BDRV_TYPE_CDROM:
            type = "cdrom";
            break;
        case BDRV_TYPE_FLOPPY:
            type = "floppy";
            break;
        }

        bs_obj = qobject_from_jsonf("{ 'device': %s, 'type': %s, "
                                    "'removable': %i, 'locked': %i }",
                                    bs->device_name, type, bs->removable,
                                    bs->locked);
        assert(bs_obj != NULL);

        if (bs->drv) {
            QObject *obj;
            QDict *bs_dict = qobject_to_qdict(bs_obj);

            obj = qobject_from_jsonf("{ 'file': %s, 'ro': %i, 'drv': %s, "
                                     "'encrypted': %i }",
                                     bs->filename, bs->read_only,
                                     bs->drv->format_name,
                                     bdrv_is_encrypted(bs));
            assert(obj != NULL);
            if (bs->backing_file[0] != '\0') {
                QDict *qdict = qobject_to_qdict(obj);
                qdict_put(qdict, "backing_file",
                          qstring_from_str(bs->backing_file));
            }

            qdict_put_obj(bs_dict, "inserted", obj);
        }
        qlist_append_obj(bs_list, bs_obj);
    }

    *ret_data = QOBJECT(bs_list);
}

static void bdrv_stats_iter(QObject *data, void *opaque)
{
    QDict *qdict;
    Monitor *mon = opaque;

    qdict = qobject_to_qdict(data);
    monitor_printf(mon, "%s:", qdict_get_str(qdict, "device"));

    qdict = qobject_to_qdict(qdict_get(qdict, "stats"));
    monitor_printf(mon, " rd_bytes=%" PRId64
                        " wr_bytes=%" PRId64
                        " rd_operations=%" PRId64
                        " wr_operations=%" PRId64
                        "\n",
                        qdict_get_int(qdict, "rd_bytes"),
                        qdict_get_int(qdict, "wr_bytes"),
                        qdict_get_int(qdict, "rd_operations"),
                        qdict_get_int(qdict, "wr_operations"));
}

void bdrv_stats_print(Monitor *mon, const QObject *data)
{
    qlist_iter(qobject_to_qlist(data), bdrv_stats_iter, mon);
}

/**
 * bdrv_info_stats(): show block device statistics
 *
 * Each device statistic information is stored in a QDict and
 * the returned QObject is a QList of all devices.
 *
 * The QDict contains the following:
 *
 * - "device": device name
 * - "stats": A QDict with the statistics information, it contains:
 *     - "rd_bytes": bytes read
 *     - "wr_bytes": bytes written
 *     - "rd_operations": read operations
 *     - "wr_operations": write operations
 * 
 * Example:
 *
 * [ { "device": "ide0-hd0",
 *               "stats": { "rd_bytes": 512,
 *                          "wr_bytes": 0,
 *                          "rd_operations": 1,
 *                          "wr_operations": 0 } },
 *   { "device": "ide1-cd0",
 *               "stats": { "rd_bytes": 0,
 *                          "wr_bytes": 0,
 *                          "rd_operations": 0,
 *                          "wr_operations": 0 } } ]
 */
void bdrv_info_stats(Monitor *mon, QObject **ret_data)
{
    QObject *obj;
    QList *devices;
    BlockDriverState *bs;

    devices = qlist_new();

    for (bs = bdrv_first; bs != NULL; bs = bs->next) {
        obj = qobject_from_jsonf("{ 'device': %s, 'stats': {"
                                 "'rd_bytes': %" PRId64 ","
                                 "'wr_bytes': %" PRId64 ","
                                 "'rd_operations': %" PRId64 ","
                                 "'wr_operations': %" PRId64
                                 "} }",
                                 bs->device_name,
                                 bs->rd_bytes, bs->wr_bytes,
                                 bs->rd_ops, bs->wr_ops);
        assert(obj != NULL);
        qlist_append_obj(devices, obj);
    }

    *ret_data = QOBJECT(devices);
}

const char *bdrv_get_encrypted_filename(BlockDriverState *bs)
{
    if (bs->backing_hd && bs->backing_hd->encrypted)
        return bs->backing_file;
    else if (bs->encrypted)
        return bs->filename;
    else
        return NULL;
}

void bdrv_get_backing_filename(BlockDriverState *bs,
                               char *filename, int filename_size)
{
    if (!bs->backing_file) {
        pstrcpy(filename, filename_size, "");
    } else {
        pstrcpy(filename, filename_size, bs->backing_file);
    }
}

int bdrv_write_compressed(BlockDriverState *bs, int64_t sector_num,
                          const uint8_t *buf, int nb_sectors)
{
    BlockDriver *drv = bs->drv;
    if (!drv)
        return -ENOMEDIUM;
    if (!drv->bdrv_write_compressed)
        return -ENOTSUP;
    if (bdrv_check_request(bs, sector_num, nb_sectors))
        return -EIO;

    if (bs->dirty_bitmap) {
        set_dirty_bitmap(bs, sector_num, nb_sectors, 1);
    }

    return drv->bdrv_write_compressed(bs, sector_num, buf, nb_sectors);
}

int bdrv_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
{
    BlockDriver *drv = bs->drv;
    if (!drv)
        return -ENOMEDIUM;
    if (!drv->bdrv_get_info)
        return -ENOTSUP;
    memset(bdi, 0, sizeof(*bdi));
    return drv->bdrv_get_info(bs, bdi);
}

int bdrv_save_vmstate(BlockDriverState *bs, const uint8_t *buf,
                      int64_t pos, int size)
{
    BlockDriver *drv = bs->drv;
    if (!drv)
        return -ENOMEDIUM;
    if (!drv->bdrv_save_vmstate)
        return -ENOTSUP;
    return drv->bdrv_save_vmstate(bs, buf, pos, size);
}

int bdrv_load_vmstate(BlockDriverState *bs, uint8_t *buf,
                      int64_t pos, int size)
{
    BlockDriver *drv = bs->drv;
    if (!drv)
        return -ENOMEDIUM;
    if (!drv->bdrv_load_vmstate)
        return -ENOTSUP;
    return drv->bdrv_load_vmstate(bs, buf, pos, size);
}

/**************************************************************/
/* handling of snapshots */

int bdrv_snapshot_create(BlockDriverState *bs,
                         QEMUSnapshotInfo *sn_info)
{
    BlockDriver *drv = bs->drv;
    if (!drv)
        return -ENOMEDIUM;
    if (!drv->bdrv_snapshot_create)
        return -ENOTSUP;
    return drv->bdrv_snapshot_create(bs, sn_info);
}

int bdrv_snapshot_goto(BlockDriverState *bs,
                       const char *snapshot_id)
{
    BlockDriver *drv = bs->drv;
    if (!drv)
        return -ENOMEDIUM;
    if (!drv->bdrv_snapshot_goto)
        return -ENOTSUP;
    return drv->bdrv_snapshot_goto(bs, snapshot_id);
}

int bdrv_snapshot_delete(BlockDriverState *bs, const char *snapshot_id)
{
    BlockDriver *drv = bs->drv;
    if (!drv)
        return -ENOMEDIUM;
    if (!drv->bdrv_snapshot_delete)
        return -ENOTSUP;
    return drv->bdrv_snapshot_delete(bs, snapshot_id);
}

int bdrv_snapshot_list(BlockDriverState *bs,
                       QEMUSnapshotInfo **psn_info)
{
    BlockDriver *drv = bs->drv;
    if (!drv)
        return -ENOMEDIUM;
    if (!drv->bdrv_snapshot_list)
        return -ENOTSUP;
    return drv->bdrv_snapshot_list(bs, psn_info);
}

#define NB_SUFFIXES 4

char *get_human_readable_size(char *buf, int buf_size, int64_t size)
{
    static const char suffixes[NB_SUFFIXES] = "KMGT";
    int64_t base;
    int i;

    if (size <= 999) {
        snprintf(buf, buf_size, "%" PRId64, size);
    } else {
        base = 1024;
        for(i = 0; i < NB_SUFFIXES; i++) {
            if (size < (10 * base)) {
                snprintf(buf, buf_size, "%0.1f%c",
                         (double)size / base,
                         suffixes[i]);
                break;
            } else if (size < (1000 * base) || i == (NB_SUFFIXES - 1)) {
                snprintf(buf, buf_size, "%" PRId64 "%c",
                         ((size + (base >> 1)) / base),
                         suffixes[i]);
                break;
            }
            base = base * 1024;
        }
    }
    return buf;
}

char *bdrv_snapshot_dump(char *buf, int buf_size, QEMUSnapshotInfo *sn)
{
    char buf1[128], date_buf[128], clock_buf[128];
#ifdef _WIN32
    struct tm *ptm;
#else
    struct tm tm;
#endif
    time_t ti;
    int64_t secs;

    if (!sn) {
        snprintf(buf, buf_size,
                 "%-10s%-20s%7s%20s%15s",
                 "ID", "TAG", "VM SIZE", "DATE", "VM CLOCK");
    } else {
        ti = sn->date_sec;
#ifdef _WIN32
        ptm = localtime(&ti);
        strftime(date_buf, sizeof(date_buf),
                 "%Y-%m-%d %H:%M:%S", ptm);
#else
        localtime_r(&ti, &tm);
        strftime(date_buf, sizeof(date_buf),
                 "%Y-%m-%d %H:%M:%S", &tm);
#endif
        secs = sn->vm_clock_nsec / 1000000000;
        snprintf(clock_buf, sizeof(clock_buf),
                 "%02d:%02d:%02d.%03d",
                 (int)(secs / 3600),
                 (int)((secs / 60) % 60),
                 (int)(secs % 60),
                 (int)((sn->vm_clock_nsec / 1000000) % 1000));
        snprintf(buf, buf_size,
                 "%-10s%-20s%7s%20s%15s",
                 sn->id_str, sn->name,
                 get_human_readable_size(buf1, sizeof(buf1), sn->vm_state_size),
                 date_buf,
                 clock_buf);
    }
    return buf;
}


/**************************************************************/
/* async I/Os */

BlockDriverAIOCB *bdrv_aio_readv(BlockDriverState *bs, int64_t sector_num,
                                 QEMUIOVector *qiov, int nb_sectors,
                                 BlockDriverCompletionFunc *cb, void *opaque)
{
    BlockDriver *drv = bs->drv;
    BlockDriverAIOCB *ret;

    if (!drv)
        return NULL;
    if (bdrv_check_request(bs, sector_num, nb_sectors))
        return NULL;

    ret = drv->bdrv_aio_readv(bs, sector_num, qiov, nb_sectors,
                              cb, opaque);

    if (ret) {
        /* Update stats even though technically transfer has not happened. */
        bs->rd_bytes += (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
        bs->rd_ops ++;
    }

    return ret;
}

BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
                                  QEMUIOVector *qiov, int nb_sectors,
                                  BlockDriverCompletionFunc *cb, void *opaque)
{
    BlockDriver *drv = bs->drv;
    BlockDriverAIOCB *ret;

    if (!drv)
        return NULL;
    if (bs->read_only)
        return NULL;
    if (bdrv_check_request(bs, sector_num, nb_sectors))
        return NULL;

    if (bs->dirty_bitmap) {
        set_dirty_bitmap(bs, sector_num, nb_sectors, 1);
    }

    ret = drv->bdrv_aio_writev(bs, sector_num, qiov, nb_sectors,
                               cb, opaque);

    if (ret) {
        /* Update stats even though technically transfer has not happened. */
        bs->wr_bytes += (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
        bs->wr_ops ++;
    }

    return ret;
}


typedef struct MultiwriteCB {
    int error;
    int num_requests;
    int num_callbacks;
    struct {
        BlockDriverCompletionFunc *cb;
        void *opaque;
        QEMUIOVector *free_qiov;
        void *free_buf;
    } callbacks[];
} MultiwriteCB;

static void multiwrite_user_cb(MultiwriteCB *mcb)
{
    int i;

    for (i = 0; i < mcb->num_callbacks; i++) {
        mcb->callbacks[i].cb(mcb->callbacks[i].opaque, mcb->error);
        qemu_free(mcb->callbacks[i].free_qiov);
        qemu_vfree(mcb->callbacks[i].free_buf);
    }
}

static void multiwrite_cb(void *opaque, int ret)
{
    MultiwriteCB *mcb = opaque;

    if (ret < 0) {
        mcb->error = ret;
        multiwrite_user_cb(mcb);
    }

    mcb->num_requests--;
    if (mcb->num_requests == 0) {
        if (mcb->error == 0) {
            multiwrite_user_cb(mcb);
        }
        qemu_free(mcb);
    }
}

static int multiwrite_req_compare(const void *a, const void *b)
{
    return (((BlockRequest*) a)->sector - ((BlockRequest*) b)->sector);
}

/*
 * Takes a bunch of requests and tries to merge them. Returns the number of
 * requests that remain after merging.
 */
static int multiwrite_merge(BlockDriverState *bs, BlockRequest *reqs,
    int num_reqs, MultiwriteCB *mcb)
{
    int i, outidx;

    // Sort requests by start sector
    qsort(reqs, num_reqs, sizeof(*reqs), &multiwrite_req_compare);

    // Check if adjacent requests touch the same clusters. If so, combine them,
    // filling up gaps with zero sectors.
    outidx = 0;
    for (i = 1; i < num_reqs; i++) {
        int merge = 0;
        int64_t oldreq_last = reqs[outidx].sector + reqs[outidx].nb_sectors;

        // This handles the cases that are valid for all block drivers, namely
        // exactly sequential writes and overlapping writes.
        if (reqs[i].sector <= oldreq_last) {
            merge = 1;
        }

        // The block driver may decide that it makes sense to combine requests
        // even if there is a gap of some sectors between them. In this case,
        // the gap is filled with zeros (therefore only applicable for yet
        // unused space in format like qcow2).
        if (!merge && bs->drv->bdrv_merge_requests) {
            merge = bs->drv->bdrv_merge_requests(bs, &reqs[outidx], &reqs[i]);
        }

        if (reqs[outidx].qiov->niov + reqs[i].qiov->niov + 1 > IOV_MAX) {
            merge = 0;
        }

        if (merge) {
            size_t size;
            QEMUIOVector *qiov = qemu_mallocz(sizeof(*qiov));
            qemu_iovec_init(qiov,
                reqs[outidx].qiov->niov + reqs[i].qiov->niov + 1);

            // Add the first request to the merged one. If the requests are
            // overlapping, drop the last sectors of the first request.
            size = (reqs[i].sector - reqs[outidx].sector) << 9;
            qemu_iovec_concat(qiov, reqs[outidx].qiov, size);

            // We might need to add some zeros between the two requests
            if (reqs[i].sector > oldreq_last) {
                size_t zero_bytes = (reqs[i].sector - oldreq_last) << 9;
                uint8_t *buf = qemu_blockalign(bs, zero_bytes);
                memset(buf, 0, zero_bytes);
                qemu_iovec_add(qiov, buf, zero_bytes);
                mcb->callbacks[i].free_buf = buf;
            }

            // Add the second request
            qemu_iovec_concat(qiov, reqs[i].qiov, reqs[i].qiov->size);

            reqs[outidx].nb_sectors += reqs[i].nb_sectors;
            reqs[outidx].qiov = qiov;

            mcb->callbacks[i].free_qiov = reqs[outidx].qiov;
        } else {
            outidx++;
            reqs[outidx].sector     = reqs[i].sector;
            reqs[outidx].nb_sectors = reqs[i].nb_sectors;
            reqs[outidx].qiov       = reqs[i].qiov;
        }
    }

    return outidx + 1;
}

/*
 * Submit multiple AIO write requests at once.
 *
 * On success, the function returns 0 and all requests in the reqs array have
 * been submitted. In error case this function returns -1, and any of the
 * requests may or may not be submitted yet. In particular, this means that the
 * callback will be called for some of the requests, for others it won't. The
 * caller must check the error field of the BlockRequest to wait for the right
 * callbacks (if error != 0, no callback will be called).
 *
 * The implementation may modify the contents of the reqs array, e.g. to merge
 * requests. However, the fields opaque and error are left unmodified as they
 * are used to signal failure for a single request to the caller.
 */
int bdrv_aio_multiwrite(BlockDriverState *bs, BlockRequest *reqs, int num_reqs)
{
    BlockDriverAIOCB *acb;
    MultiwriteCB *mcb;
    int i;

    if (num_reqs == 0) {
        return 0;
    }

    // Create MultiwriteCB structure
    mcb = qemu_mallocz(sizeof(*mcb) + num_reqs * sizeof(*mcb->callbacks));
    mcb->num_requests = 0;
    mcb->num_callbacks = num_reqs;

    for (i = 0; i < num_reqs; i++) {
        mcb->callbacks[i].cb = reqs[i].cb;
        mcb->callbacks[i].opaque = reqs[i].opaque;
    }

    // Check for mergable requests
    num_reqs = multiwrite_merge(bs, reqs, num_reqs, mcb);

    // Run the aio requests
    for (i = 0; i < num_reqs; i++) {
        acb = bdrv_aio_writev(bs, reqs[i].sector, reqs[i].qiov,
            reqs[i].nb_sectors, multiwrite_cb, mcb);

        if (acb == NULL) {
            // We can only fail the whole thing if no request has been
            // submitted yet. Otherwise we'll wait for the submitted AIOs to
            // complete and report the error in the callback.
            if (mcb->num_requests == 0) {
                reqs[i].error = EIO;
                goto fail;
            } else {
                mcb->error = EIO;
                break;
            }
        } else {
            mcb->num_requests++;
        }
    }

    return 0;

fail:
    free(mcb);
    return -1;
}

BlockDriverAIOCB *bdrv_aio_flush(BlockDriverState *bs,
        BlockDriverCompletionFunc *cb, void *opaque)
{
    BlockDriver *drv = bs->drv;

    if (!drv)
        return NULL;
    return drv->bdrv_aio_flush(bs, cb, opaque);
}

void bdrv_aio_cancel(BlockDriverAIOCB *acb)
{
    acb->pool->cancel(acb);
}


/**************************************************************/
/* async block device emulation */

typedef struct BlockDriverAIOCBSync {
    BlockDriverAIOCB common;
    QEMUBH *bh;
    int ret;
    /* vector translation state */
    QEMUIOVector *qiov;
    uint8_t *bounce;
    int is_write;
} BlockDriverAIOCBSync;

static void bdrv_aio_cancel_em(BlockDriverAIOCB *blockacb)
{
    BlockDriverAIOCBSync *acb = (BlockDriverAIOCBSync *)blockacb;
    qemu_bh_delete(acb->bh);
    acb->bh = NULL;
    qemu_aio_release(acb);
}

static AIOPool bdrv_em_aio_pool = {
    .aiocb_size         = sizeof(BlockDriverAIOCBSync),
    .cancel             = bdrv_aio_cancel_em,
};

static void bdrv_aio_bh_cb(void *opaque)
{
    BlockDriverAIOCBSync *acb = opaque;

    if (!acb->is_write)
        qemu_iovec_from_buffer(acb->qiov, acb->bounce, acb->qiov->size);
    qemu_vfree(acb->bounce);
    acb->common.cb(acb->common.opaque, acb->ret);
    qemu_bh_delete(acb->bh);
    acb->bh = NULL;
    qemu_aio_release(acb);
}

static BlockDriverAIOCB *bdrv_aio_rw_vector(BlockDriverState *bs,
                                            int64_t sector_num,
                                            QEMUIOVector *qiov,
                                            int nb_sectors,
                                            BlockDriverCompletionFunc *cb,
                                            void *opaque,
                                            int is_write)

{
    BlockDriverAIOCBSync *acb;

    acb = qemu_aio_get(&bdrv_em_aio_pool, bs, cb, opaque);
    acb->is_write = is_write;
    acb->qiov = qiov;
    acb->bounce = qemu_blockalign(bs, qiov->size);

    if (!acb->bh)
        acb->bh = qemu_bh_new(bdrv_aio_bh_cb, acb);

    if (is_write) {
        qemu_iovec_to_buffer(acb->qiov, acb->bounce);
        acb->ret = bdrv_write(bs, sector_num, acb->bounce, nb_sectors);
    } else {
        acb->ret = bdrv_read(bs, sector_num, acb->bounce, nb_sectors);
    }

    qemu_bh_schedule(acb->bh);

    return &acb->common;
}

static BlockDriverAIOCB *bdrv_aio_readv_em(BlockDriverState *bs,
        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
        BlockDriverCompletionFunc *cb, void *opaque)
{
    return bdrv_aio_rw_vector(bs, sector_num, qiov, nb_sectors, cb, opaque, 0);
}

static BlockDriverAIOCB *bdrv_aio_writev_em(BlockDriverState *bs,
        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
        BlockDriverCompletionFunc *cb, void *opaque)
{
    return bdrv_aio_rw_vector(bs, sector_num, qiov, nb_sectors, cb, opaque, 1);
}

static BlockDriverAIOCB *bdrv_aio_flush_em(BlockDriverState *bs,
        BlockDriverCompletionFunc *cb, void *opaque)
{
    BlockDriverAIOCBSync *acb;

    acb = qemu_aio_get(&bdrv_em_aio_pool, bs, cb, opaque);
    acb->is_write = 1; /* don't bounce in the completion hadler */
    acb->qiov = NULL;
    acb->bounce = NULL;
    acb->ret = 0;

    if (!acb->bh)
        acb->bh = qemu_bh_new(bdrv_aio_bh_cb, acb);

    bdrv_flush(bs);
    qemu_bh_schedule(acb->bh);
    return &acb->common;
}

/**************************************************************/
/* sync block device emulation */

static void bdrv_rw_em_cb(void *opaque, int ret)
{
    *(int *)opaque = ret;
}

#define NOT_DONE 0x7fffffff

static int bdrv_read_em(BlockDriverState *bs, int64_t sector_num,
                        uint8_t *buf, int nb_sectors)
{
    int async_ret;
    BlockDriverAIOCB *acb;
    struct iovec iov;
    QEMUIOVector qiov;

    async_context_push();

    async_ret = NOT_DONE;
    iov.iov_base = (void *)buf;
    iov.iov_len = nb_sectors * 512;
    qemu_iovec_init_external(&qiov, &iov, 1);
    acb = bdrv_aio_readv(bs, sector_num, &qiov, nb_sectors,
        bdrv_rw_em_cb, &async_ret);
    if (acb == NULL) {
        async_ret = -1;
        goto fail;
    }

    while (async_ret == NOT_DONE) {
        qemu_aio_wait();
    }


fail:
    async_context_pop();
    return async_ret;
}

static int bdrv_write_em(BlockDriverState *bs, int64_t sector_num,
                         const uint8_t *buf, int nb_sectors)
{
    int async_ret;
    BlockDriverAIOCB *acb;
    struct iovec iov;
    QEMUIOVector qiov;

    async_context_push();

    async_ret = NOT_DONE;
    iov.iov_base = (void *)buf;
    iov.iov_len = nb_sectors * 512;
    qemu_iovec_init_external(&qiov, &iov, 1);
    acb = bdrv_aio_writev(bs, sector_num, &qiov, nb_sectors,
        bdrv_rw_em_cb, &async_ret);
    if (acb == NULL) {
        async_ret = -1;
        goto fail;
    }
    while (async_ret == NOT_DONE) {
        qemu_aio_wait();
    }

fail:
    async_context_pop();
    return async_ret;
}

void bdrv_init(void)
{
    module_call_init(MODULE_INIT_BLOCK);
}

void bdrv_init_with_whitelist(void)
{
    use_bdrv_whitelist = 1;
    bdrv_init();
}

void *qemu_aio_get(AIOPool *pool, BlockDriverState *bs,
                   BlockDriverCompletionFunc *cb, void *opaque)
{
    BlockDriverAIOCB *acb;

    if (pool->free_aiocb) {
        acb = pool->free_aiocb;
        pool->free_aiocb = acb->next;
    } else {
        acb = qemu_mallocz(pool->aiocb_size);
        acb->pool = pool;
    }
    acb->bs = bs;
    acb->cb = cb;
    acb->opaque = opaque;
    return acb;
}

void qemu_aio_release(void *p)
{
    BlockDriverAIOCB *acb = (BlockDriverAIOCB *)p;
    AIOPool *pool = acb->pool;
    acb->next = pool->free_aiocb;
    pool->free_aiocb = acb;
}

/**************************************************************/
/* removable device support */

/**
 * Return TRUE if the media is present
 */
int bdrv_is_inserted(BlockDriverState *bs)
{
    BlockDriver *drv = bs->drv;
    int ret;
    if (!drv)
        return 0;
    if (!drv->bdrv_is_inserted)
        return 1;
    ret = drv->bdrv_is_inserted(bs);
    return ret;
}

/**
 * Return TRUE if the media changed since the last call to this
 * function. It is currently only used for floppy disks
 */
int bdrv_media_changed(BlockDriverState *bs)
{
    BlockDriver *drv = bs->drv;
    int ret;

    if (!drv || !drv->bdrv_media_changed)
        ret = -ENOTSUP;
    else
        ret = drv->bdrv_media_changed(bs);
    if (ret == -ENOTSUP)
        ret = bs->media_changed;
    bs->media_changed = 0;
    return ret;
}

/**
 * If eject_flag is TRUE, eject the media. Otherwise, close the tray
 */
int bdrv_eject(BlockDriverState *bs, int eject_flag)
{
    BlockDriver *drv = bs->drv;
    int ret;

    if (bs->locked) {
        return -EBUSY;
    }

    if (!drv || !drv->bdrv_eject) {
        ret = -ENOTSUP;
    } else {
        ret = drv->bdrv_eject(bs, eject_flag);
    }
    if (ret == -ENOTSUP) {
        if (eject_flag)
            bdrv_close(bs);
        ret = 0;
    }

    return ret;
}

int bdrv_is_locked(BlockDriverState *bs)
{
    return bs->locked;
}

/**
 * Lock or unlock the media (if it is locked, the user won't be able
 * to eject it manually).
 */
void bdrv_set_locked(BlockDriverState *bs, int locked)
{
    BlockDriver *drv = bs->drv;

    bs->locked = locked;
    if (drv && drv->bdrv_set_locked) {
        drv->bdrv_set_locked(bs, locked);
    }
}

/* needed for generic scsi interface */

int bdrv_ioctl(BlockDriverState *bs, unsigned long int req, void *buf)
{
    BlockDriver *drv = bs->drv;

    if (drv && drv->bdrv_ioctl)
        return drv->bdrv_ioctl(bs, req, buf);
    return -ENOTSUP;
}

BlockDriverAIOCB *bdrv_aio_ioctl(BlockDriverState *bs,
        unsigned long int req, void *buf,
        BlockDriverCompletionFunc *cb, void *opaque)
{
    BlockDriver *drv = bs->drv;

    if (drv && drv->bdrv_aio_ioctl)
        return drv->bdrv_aio_ioctl(bs, req, buf, cb, opaque);
    return NULL;
}



void *qemu_blockalign(BlockDriverState *bs, size_t size)
{
    return qemu_memalign((bs && bs->buffer_alignment) ? bs->buffer_alignment : 512, size);
}

void bdrv_set_dirty_tracking(BlockDriverState *bs, int enable)
{
    int64_t bitmap_size;

    bs->dirty_count = 0;
    if (enable) {
        if (!bs->dirty_bitmap) {
            bitmap_size = (bdrv_getlength(bs) >> BDRV_SECTOR_BITS) +
                    BDRV_SECTORS_PER_DIRTY_CHUNK * 8 - 1;
            bitmap_size /= BDRV_SECTORS_PER_DIRTY_CHUNK * 8;

            bs->dirty_bitmap = qemu_mallocz(bitmap_size);
        }
    } else {
        if (bs->dirty_bitmap) {
            qemu_free(bs->dirty_bitmap);
            bs->dirty_bitmap = NULL;
        }
    }
}

int bdrv_get_dirty(BlockDriverState *bs, int64_t sector)
{
    int64_t chunk = sector / (int64_t)BDRV_SECTORS_PER_DIRTY_CHUNK;

    if (bs->dirty_bitmap &&
        (sector << BDRV_SECTOR_BITS) < bdrv_getlength(bs)) {
        return bs->dirty_bitmap[chunk / (sizeof(unsigned long) * 8)] &
            (1 << (chunk % (sizeof(unsigned long) * 8)));
    } else {
        return 0;
    }
}

void bdrv_reset_dirty(BlockDriverState *bs, int64_t cur_sector,
                      int nr_sectors)
{
    set_dirty_bitmap(bs, cur_sector, nr_sectors, 0);
}

int64_t bdrv_get_dirty_count(BlockDriverState *bs)
{
    return bs->dirty_count;
}