xref: /openbmc/qemu/block/rbd.c (revision f27aaf4b531bc0eb4f3e1f7accf4931cae36db0d)

/*
 * QEMU Block driver for RADOS (Ceph)
 *
 * Copyright (C) 2010 Christian Brunner <chb@muc.de>
 *
 * This work is licensed under the terms of the GNU GPL, version 2.  See
 * the COPYING file in the top-level directory.
 *
 */

#include "qemu-common.h"
#include "qemu-error.h"

#include "rbd_types.h"
#include "block_int.h"

#include <rados/librados.h>



/*
 * When specifying the image filename use:
 *
 * rbd:poolname/devicename
 *
 * poolname must be the name of an existing rados pool
 *
 * devicename is the basename for all objects used to
 * emulate the raw device.
 *
 * Metadata information (image size, ...) is stored in an
 * object with the name "devicename.rbd".
 *
 * The raw device is split into 4MB sized objects by default.
 * The sequencenumber is encoded in a 12 byte long hex-string,
 * and is attached to the devicename, separated by a dot.
 * e.g. "devicename.1234567890ab"
 *
 */

#define OBJ_MAX_SIZE (1UL << OBJ_DEFAULT_OBJ_ORDER)

typedef struct RBDAIOCB {
    BlockDriverAIOCB common;
    QEMUBH *bh;
    int ret;
    QEMUIOVector *qiov;
    char *bounce;
    int write;
    int64_t sector_num;
    int aiocnt;
    int error;
    struct BDRVRBDState *s;
    int cancelled;
} RBDAIOCB;

typedef struct RADOSCB {
    int rcbid;
    RBDAIOCB *acb;
    struct BDRVRBDState *s;
    int done;
    int64_t segsize;
    char *buf;
    int ret;
} RADOSCB;

#define RBD_FD_READ 0
#define RBD_FD_WRITE 1

typedef struct BDRVRBDState {
    int fds[2];
    rados_pool_t pool;
    rados_pool_t header_pool;
    char name[RBD_MAX_OBJ_NAME_SIZE];
    char block_name[RBD_MAX_BLOCK_NAME_SIZE];
    uint64_t size;
    uint64_t objsize;
    int qemu_aio_count;
    int event_reader_pos;
    RADOSCB *event_rcb;
} BDRVRBDState;

typedef struct rbd_obj_header_ondisk RbdHeader1;

static void rbd_aio_bh_cb(void *opaque);

static int rbd_next_tok(char *dst, int dst_len,
                        char *src, char delim,
                        const char *name,
                        char **p)
{
    int l;
    char *end;

    *p = NULL;

    if (delim != '\0') {
        end = strchr(src, delim);
        if (end) {
            *p = end + 1;
            *end = '\0';
        }
    }
    l = strlen(src);
    if (l >= dst_len) {
        error_report("%s too long", name);
        return -EINVAL;
    } else if (l == 0) {
        error_report("%s too short", name);
        return -EINVAL;
    }

    pstrcpy(dst, dst_len, src);

    return 0;
}

static int rbd_parsename(const char *filename,
                         char *pool, int pool_len,
                         char *snap, int snap_len,
                         char *name, int name_len)
{
    const char *start;
    char *p, *buf;
    int ret;

    if (!strstart(filename, "rbd:", &start)) {
        return -EINVAL;
    }

    buf = qemu_strdup(start);
    p = buf;

    ret = rbd_next_tok(pool, pool_len, p, '/', "pool name", &p);
    if (ret < 0 || !p) {
        ret = -EINVAL;
        goto done;
    }
    ret = rbd_next_tok(name, name_len, p, '@', "object name", &p);
    if (ret < 0) {
        goto done;
    }
    if (!p) {
        *snap = '\0';
        goto done;
    }

    ret = rbd_next_tok(snap, snap_len, p, '\0', "snap name", &p);

done:
    qemu_free(buf);
    return ret;
}

static int create_tmap_op(uint8_t op, const char *name, char **tmap_desc)
{
    uint32_t len = strlen(name);
    uint32_t len_le = cpu_to_le32(len);
    /* total_len = encoding op + name + empty buffer */
    uint32_t total_len = 1 + (sizeof(uint32_t) + len) + sizeof(uint32_t);
    uint8_t *desc = NULL;

    desc = qemu_malloc(total_len);

    *tmap_desc = (char *)desc;

    *desc = op;
    desc++;
    memcpy(desc, &len_le, sizeof(len_le));
    desc += sizeof(len_le);
    memcpy(desc, name, len);
    desc += len;
    len = 0; /* no need for endian conversion for 0 */
    memcpy(desc, &len, sizeof(len));
    desc += sizeof(len);

    return (char *)desc - *tmap_desc;
}

static void free_tmap_op(char *tmap_desc)
{
    qemu_free(tmap_desc);
}

static int rbd_register_image(rados_pool_t pool, const char *name)
{
    char *tmap_desc;
    const char *dir = RBD_DIRECTORY;
    int ret;

    ret = create_tmap_op(CEPH_OSD_TMAP_SET, name, &tmap_desc);
    if (ret < 0) {
        return ret;
    }

    ret = rados_tmap_update(pool, dir, tmap_desc, ret);
    free_tmap_op(tmap_desc);

    return ret;
}

static int touch_rbd_info(rados_pool_t pool, const char *info_oid)
{
    int r = rados_write(pool, info_oid, 0, NULL, 0);
    if (r < 0) {
        return r;
    }
    return 0;
}

static int rbd_assign_bid(rados_pool_t pool, uint64_t *id)
{
    uint64_t out[1];
    const char *info_oid = RBD_INFO;

    *id = 0;

    int r = touch_rbd_info(pool, info_oid);
    if (r < 0) {
        return r;
    }

    r = rados_exec(pool, info_oid, "rbd", "assign_bid", NULL,
                   0, (char *)out, sizeof(out));
    if (r < 0) {
        return r;
    }

    le64_to_cpus(out);
    *id = out[0];

    return 0;
}

static int rbd_create(const char *filename, QEMUOptionParameter *options)
{
    int64_t bytes = 0;
    int64_t objsize;
    uint64_t size;
    time_t mtime;
    uint8_t obj_order = RBD_DEFAULT_OBJ_ORDER;
    char pool[RBD_MAX_SEG_NAME_SIZE];
    char n[RBD_MAX_SEG_NAME_SIZE];
    char name[RBD_MAX_OBJ_NAME_SIZE];
    char snap_buf[RBD_MAX_SEG_NAME_SIZE];
    char *snap = NULL;
    RbdHeader1 header;
    rados_pool_t p;
    uint64_t bid;
    uint32_t hi, lo;
    int ret;

    if (rbd_parsename(filename,
                      pool, sizeof(pool),
                      snap_buf, sizeof(snap_buf),
                      name, sizeof(name)) < 0) {
        return -EINVAL;
    }
    if (snap_buf[0] != '\0') {
        snap = snap_buf;
    }

    snprintf(n, sizeof(n), "%s%s", name, RBD_SUFFIX);

    /* Read out options */
    while (options && options->name) {
        if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
            bytes = options->value.n;
        } else if (!strcmp(options->name, BLOCK_OPT_CLUSTER_SIZE)) {
            if (options->value.n) {
                objsize = options->value.n;
                if ((objsize - 1) & objsize) {    /* not a power of 2? */
                    error_report("obj size needs to be power of 2");
                    return -EINVAL;
                }
                if (objsize < 4096) {
                    error_report("obj size too small");
                    return -EINVAL;
                }
		obj_order = ffs(objsize) - 1;
            }
        }
        options++;
    }

    memset(&header, 0, sizeof(header));
    pstrcpy(header.text, sizeof(header.text), RBD_HEADER_TEXT);
    pstrcpy(header.signature, sizeof(header.signature), RBD_HEADER_SIGNATURE);
    pstrcpy(header.version, sizeof(header.version), RBD_HEADER_VERSION);
    header.image_size = cpu_to_le64(bytes);
    header.options.order = obj_order;
    header.options.crypt_type = RBD_CRYPT_NONE;
    header.options.comp_type = RBD_COMP_NONE;
    header.snap_seq = 0;
    header.snap_count = 0;

    if (rados_initialize(0, NULL) < 0) {
        error_report("error initializing");
        return -EIO;
    }

    if (rados_open_pool(pool, &p)) {
        error_report("error opening pool %s", pool);
        rados_deinitialize();
        return -EIO;
    }

    /* check for existing rbd header file */
    ret = rados_stat(p, n, &size, &mtime);
    if (ret == 0) {
        ret=-EEXIST;
        goto done;
    }

    ret = rbd_assign_bid(p, &bid);
    if (ret < 0) {
        error_report("failed assigning block id");
        rados_deinitialize();
        return -EIO;
    }
    hi = bid >> 32;
    lo = bid & 0xFFFFFFFF;
    snprintf(header.block_name, sizeof(header.block_name), "rb.%x.%x", hi, lo);

    /* create header file */
    ret = rados_write(p, n, 0, (const char *)&header, sizeof(header));
    if (ret < 0) {
        goto done;
    }

    ret = rbd_register_image(p, name);
done:
    rados_close_pool(p);
    rados_deinitialize();

    return ret;
}

/*
 * This aio completion is being called from rbd_aio_event_reader() and
 * runs in qemu context. It schedules a bh, but just in case the aio
 * was not cancelled before.
 */
static void rbd_complete_aio(RADOSCB *rcb)
{
    RBDAIOCB *acb = rcb->acb;
    int64_t r;

    acb->aiocnt--;

    if (acb->cancelled) {
        if (!acb->aiocnt) {
            qemu_vfree(acb->bounce);
            qemu_aio_release(acb);
        }
        goto done;
    }

    r = rcb->ret;

    if (acb->write) {
        if (r < 0) {
            acb->ret = r;
            acb->error = 1;
        } else if (!acb->error) {
            acb->ret += rcb->segsize;
        }
    } else {
        if (r == -ENOENT) {
            memset(rcb->buf, 0, rcb->segsize);
            if (!acb->error) {
                acb->ret += rcb->segsize;
            }
        } else if (r < 0) {
	    memset(rcb->buf, 0, rcb->segsize);
            acb->ret = r;
            acb->error = 1;
        } else if (r < rcb->segsize) {
            memset(rcb->buf + r, 0, rcb->segsize - r);
            if (!acb->error) {
                acb->ret += rcb->segsize;
            }
        } else if (!acb->error) {
            acb->ret += r;
        }
    }
    /* Note that acb->bh can be NULL in case where the aio was cancelled */
    if (!acb->aiocnt) {
        acb->bh = qemu_bh_new(rbd_aio_bh_cb, acb);
        qemu_bh_schedule(acb->bh);
    }
done:
    qemu_free(rcb);
}

/*
 * aio fd read handler. It runs in the qemu context and calls the
 * completion handling of completed rados aio operations.
 */
static void rbd_aio_event_reader(void *opaque)
{
    BDRVRBDState *s = opaque;

    ssize_t ret;

    do {
        char *p = (char *)&s->event_rcb;

        /* now read the rcb pointer that was sent from a non qemu thread */
        if ((ret = read(s->fds[RBD_FD_READ], p + s->event_reader_pos,
                        sizeof(s->event_rcb) - s->event_reader_pos)) > 0) {
            if (ret > 0) {
                s->event_reader_pos += ret;
                if (s->event_reader_pos == sizeof(s->event_rcb)) {
                    s->event_reader_pos = 0;
                    rbd_complete_aio(s->event_rcb);
                    s->qemu_aio_count --;
                }
            }
        }
    } while (ret < 0 && errno == EINTR);
}

static int rbd_aio_flush_cb(void *opaque)
{
    BDRVRBDState *s = opaque;

    return (s->qemu_aio_count > 0);
}


static int rbd_set_snapc(rados_pool_t pool, const char *snap, RbdHeader1 *header)
{
    uint32_t snap_count = le32_to_cpu(header->snap_count);
    rados_snap_t *snaps = NULL;
    rados_snap_t seq;
    uint32_t i;
    uint64_t snap_names_len = le64_to_cpu(header->snap_names_len);
    int r;
    rados_snap_t snapid = 0;

    if (snap_count) {
        const char *header_snap = (const char *)&header->snaps[snap_count];
        const char *end = header_snap + snap_names_len;
        snaps = qemu_malloc(sizeof(rados_snap_t) * header->snap_count);

        for (i=0; i < snap_count; i++) {
            snaps[i] = le64_to_cpu(header->snaps[i].id);

            if (snap && strcmp(snap, header_snap) == 0) {
                snapid = snaps[i];
            }

            header_snap += strlen(header_snap) + 1;
            if (header_snap > end) {
                error_report("bad header, snapshot list broken");
            }
        }
    }

    if (snap && !snapid) {
        error_report("snapshot not found");
        qemu_free(snaps);
        return -ENOENT;
    }
    seq = le32_to_cpu(header->snap_seq);

    r = rados_set_snap_context(pool, seq, snaps, snap_count);

    rados_set_snap(pool, snapid);

    qemu_free(snaps);

    return r;
}

#define BUF_READ_START_LEN    4096

static int rbd_read_header(BDRVRBDState *s, char **hbuf)
{
    char *buf = NULL;
    char n[RBD_MAX_SEG_NAME_SIZE];
    uint64_t len = BUF_READ_START_LEN;
    int r;

    snprintf(n, sizeof(n), "%s%s", s->name, RBD_SUFFIX);

    buf = qemu_malloc(len);

    r = rados_read(s->header_pool, n, 0, buf, len);
    if (r < 0) {
        goto failed;
    }

    if (r < len) {
        goto done;
    }

    qemu_free(buf);
    buf = qemu_malloc(len);

    r = rados_stat(s->header_pool, n, &len, NULL);
    if (r < 0) {
        goto failed;
    }

    r = rados_read(s->header_pool, n, 0, buf, len);
    if (r < 0) {
        goto failed;
    }

done:
    *hbuf = buf;
    return 0;

failed:
    qemu_free(buf);
    return r;
}

static int rbd_open(BlockDriverState *bs, const char *filename, int flags)
{
    BDRVRBDState *s = bs->opaque;
    RbdHeader1 *header;
    char pool[RBD_MAX_SEG_NAME_SIZE];
    char snap_buf[RBD_MAX_SEG_NAME_SIZE];
    char *snap = NULL;
    char *hbuf = NULL;
    int r;

    if (rbd_parsename(filename, pool, sizeof(pool),
                      snap_buf, sizeof(snap_buf),
                      s->name, sizeof(s->name)) < 0) {
        return -EINVAL;
    }
    if (snap_buf[0] != '\0') {
        snap = snap_buf;
    }

    if ((r = rados_initialize(0, NULL)) < 0) {
        error_report("error initializing");
        return r;
    }

    if ((r = rados_open_pool(pool, &s->pool))) {
        error_report("error opening pool %s", pool);
        rados_deinitialize();
        return r;
    }

    if ((r = rados_open_pool(pool, &s->header_pool))) {
        error_report("error opening pool %s", pool);
        rados_deinitialize();
        return r;
    }

    if ((r = rbd_read_header(s, &hbuf)) < 0) {
        error_report("error reading header from %s", s->name);
        goto failed;
    }

    if (memcmp(hbuf + 64, RBD_HEADER_SIGNATURE, 4)) {
        error_report("Invalid header signature");
        r = -EMEDIUMTYPE;
        goto failed;
    }

    if (memcmp(hbuf + 68, RBD_HEADER_VERSION, 8)) {
        error_report("Unknown image version");
        r = -EMEDIUMTYPE;
        goto failed;
    }

    header = (RbdHeader1 *) hbuf;
    s->size = le64_to_cpu(header->image_size);
    s->objsize = 1ULL << header->options.order;
    memcpy(s->block_name, header->block_name, sizeof(header->block_name));

    r = rbd_set_snapc(s->pool, snap, header);
    if (r < 0) {
        error_report("failed setting snap context: %s", strerror(-r));
        goto failed;
    }

    bs->read_only = (snap != NULL);

    s->event_reader_pos = 0;
    r = qemu_pipe(s->fds);
    if (r < 0) {
        error_report("error opening eventfd");
        goto failed;
    }
    fcntl(s->fds[0], F_SETFL, O_NONBLOCK);
    fcntl(s->fds[1], F_SETFL, O_NONBLOCK);
    qemu_aio_set_fd_handler(s->fds[RBD_FD_READ], rbd_aio_event_reader, NULL,
        rbd_aio_flush_cb, NULL, s);

    qemu_free(hbuf);

    return 0;

failed:
    qemu_free(hbuf);

    rados_close_pool(s->header_pool);
    rados_close_pool(s->pool);
    rados_deinitialize();
    return r;
}

static void rbd_close(BlockDriverState *bs)
{
    BDRVRBDState *s = bs->opaque;

    close(s->fds[0]);
    close(s->fds[1]);
    qemu_aio_set_fd_handler(s->fds[RBD_FD_READ], NULL , NULL, NULL, NULL,
        NULL);

    rados_close_pool(s->header_pool);
    rados_close_pool(s->pool);
    rados_deinitialize();
}

/*
 * Cancel aio. Since we don't reference acb in a non qemu threads,
 * it is safe to access it here.
 */
static void rbd_aio_cancel(BlockDriverAIOCB *blockacb)
{
    RBDAIOCB *acb = (RBDAIOCB *) blockacb;
    acb->cancelled = 1;
}

static AIOPool rbd_aio_pool = {
    .aiocb_size = sizeof(RBDAIOCB),
    .cancel = rbd_aio_cancel,
};

/*
 * This is the callback function for rados_aio_read and _write
 *
 * Note: this function is being called from a non qemu thread so
 * we need to be careful about what we do here. Generally we only
 * write to the block notification pipe, and do the rest of the
 * io completion handling from rbd_aio_event_reader() which
 * runs in a qemu context.
 */
static void rbd_finish_aiocb(rados_completion_t c, RADOSCB *rcb)
{
    int ret;
    rcb->ret = rados_aio_get_return_value(c);
    rados_aio_release(c);
    while (1) {
        fd_set wfd;
        int fd = rcb->s->fds[RBD_FD_WRITE];

        /* send the rcb pointer to the qemu thread that is responsible
           for the aio completion. Must do it in a qemu thread context */
        ret = write(fd, (void *)&rcb, sizeof(rcb));
        if (ret >= 0) {
            break;
        }
        if (errno == EINTR) {
            continue;
	}
        if (errno != EAGAIN) {
            break;
	}

        FD_ZERO(&wfd);
        FD_SET(fd, &wfd);
        do {
            ret = select(fd + 1, NULL, &wfd, NULL, NULL);
        } while (ret < 0 && errno == EINTR);
    }

    if (ret < 0) {
        error_report("failed writing to acb->s->fds\n");
        qemu_free(rcb);
    }
}

/* Callback when all queued rados_aio requests are complete */

static void rbd_aio_bh_cb(void *opaque)
{
    RBDAIOCB *acb = opaque;

    if (!acb->write) {
        qemu_iovec_from_buffer(acb->qiov, acb->bounce, acb->qiov->size);
    }
    qemu_vfree(acb->bounce);
    acb->common.cb(acb->common.opaque, (acb->ret > 0 ? 0 : acb->ret));
    qemu_bh_delete(acb->bh);
    acb->bh = NULL;

    qemu_aio_release(acb);
}

static BlockDriverAIOCB *rbd_aio_rw_vector(BlockDriverState *bs,
                                           int64_t sector_num,
                                           QEMUIOVector *qiov,
                                           int nb_sectors,
                                           BlockDriverCompletionFunc *cb,
                                           void *opaque, int write)
{
    RBDAIOCB *acb;
    RADOSCB *rcb;
    rados_completion_t c;
    char n[RBD_MAX_SEG_NAME_SIZE];
    int64_t segnr, segoffs, segsize, last_segnr;
    int64_t off, size;
    char *buf;

    BDRVRBDState *s = bs->opaque;

    acb = qemu_aio_get(&rbd_aio_pool, bs, cb, opaque);
    acb->write = write;
    acb->qiov = qiov;
    acb->bounce = qemu_blockalign(bs, qiov->size);
    acb->aiocnt = 0;
    acb->ret = 0;
    acb->error = 0;
    acb->s = s;
    acb->cancelled = 0;
    acb->bh = NULL;

    if (write) {
        qemu_iovec_to_buffer(acb->qiov, acb->bounce);
    }

    buf = acb->bounce;

    off = sector_num * BDRV_SECTOR_SIZE;
    size = nb_sectors * BDRV_SECTOR_SIZE;
    segnr = off / s->objsize;
    segoffs = off % s->objsize;
    segsize = s->objsize - segoffs;

    last_segnr = ((off + size - 1) / s->objsize);
    acb->aiocnt = (last_segnr - segnr) + 1;

    s->qemu_aio_count += acb->aiocnt; /* All the RADOSCB */

    while (size > 0) {
        if (size < segsize) {
            segsize = size;
        }

        snprintf(n, sizeof(n), "%s.%012" PRIx64, s->block_name,
                 segnr);

        rcb = qemu_malloc(sizeof(RADOSCB));
        rcb->done = 0;
        rcb->acb = acb;
        rcb->segsize = segsize;
        rcb->buf = buf;
        rcb->s = acb->s;

        if (write) {
            rados_aio_create_completion(rcb, NULL,
                                        (rados_callback_t) rbd_finish_aiocb,
                                        &c);
            rados_aio_write(s->pool, n, segoffs, buf, segsize, c);
        } else {
            rados_aio_create_completion(rcb,
                                        (rados_callback_t) rbd_finish_aiocb,
                                        NULL, &c);
            rados_aio_read(s->pool, n, segoffs, buf, segsize, c);
        }

        buf += segsize;
        size -= segsize;
        segoffs = 0;
        segsize = s->objsize;
        segnr++;
    }

    return &acb->common;
}

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

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

static int rbd_getinfo(BlockDriverState * bs, BlockDriverInfo * bdi)
{
    BDRVRBDState *s = bs->opaque;
    bdi->cluster_size = s->objsize;
    return 0;
}

static int64_t rbd_getlength(BlockDriverState * bs)
{
    BDRVRBDState *s = bs->opaque;

    return s->size;
}

static int rbd_snap_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
{
    BDRVRBDState *s = bs->opaque;
    char inbuf[512], outbuf[128];
    uint64_t snap_id;
    int r;
    char *p = inbuf;
    char *end = inbuf + sizeof(inbuf);
    char n[RBD_MAX_SEG_NAME_SIZE];
    char *hbuf = NULL;
    RbdHeader1 *header;

    if (sn_info->name[0] == '\0') {
        return -EINVAL; /* we need a name for rbd snapshots */
    }

    /*
     * rbd snapshots are using the name as the user controlled unique identifier
     * we can't use the rbd snapid for that purpose, as it can't be set
     */
    if (sn_info->id_str[0] != '\0' &&
        strcmp(sn_info->id_str, sn_info->name) != 0) {
        return -EINVAL;
    }

    if (strlen(sn_info->name) >= sizeof(sn_info->id_str)) {
        return -ERANGE;
    }

    r = rados_selfmanaged_snap_create(s->header_pool, &snap_id);
    if (r < 0) {
        error_report("failed to create snap id: %s", strerror(-r));
        return r;
    }

    *(uint32_t *)p = strlen(sn_info->name);
    cpu_to_le32s((uint32_t *)p);
    p += sizeof(uint32_t);
    strncpy(p, sn_info->name, end - p);
    p += strlen(p);
    if (p + sizeof(snap_id) > end) {
        error_report("invalid input parameter");
        return -EINVAL;
    }

    *(uint64_t *)p = snap_id;
    cpu_to_le64s((uint64_t *)p);

    snprintf(n, sizeof(n), "%s%s", s->name, RBD_SUFFIX);

    r = rados_exec(s->header_pool, n, "rbd", "snap_add", inbuf,
                   sizeof(inbuf), outbuf, sizeof(outbuf));
    if (r < 0) {
        error_report("rbd.snap_add execution failed failed: %s", strerror(-r));
        return r;
    }

    sprintf(sn_info->id_str, "%s", sn_info->name);

    r = rbd_read_header(s, &hbuf);
    if (r < 0) {
        error_report("failed reading header: %s", strerror(-r));
        return r;
    }

    header = (RbdHeader1 *) hbuf;
    r = rbd_set_snapc(s->pool, sn_info->name, header);
    if (r < 0) {
        error_report("failed setting snap context: %s", strerror(-r));
        goto failed;
    }

    return 0;

failed:
    qemu_free(header);
    return r;
}

static int decode32(char **p, const char *end, uint32_t *v)
{
    if (*p + 4 > end) {
	return -ERANGE;
    }

    *v = *(uint32_t *)(*p);
    le32_to_cpus(v);
    *p += 4;
    return 0;
}

static int decode64(char **p, const char *end, uint64_t *v)
{
    if (*p + 8 > end) {
        return -ERANGE;
    }

    *v = *(uint64_t *)(*p);
    le64_to_cpus(v);
    *p += 8;
    return 0;
}

static int decode_str(char **p, const char *end, char **s)
{
    uint32_t len;
    int r;

    if ((r = decode32(p, end, &len)) < 0) {
        return r;
    }

    *s = qemu_malloc(len + 1);
    memcpy(*s, *p, len);
    *p += len;
    (*s)[len] = '\0';

    return len;
}

static int rbd_snap_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
{
    BDRVRBDState *s = bs->opaque;
    char n[RBD_MAX_SEG_NAME_SIZE];
    QEMUSnapshotInfo *sn_info, *sn_tab = NULL;
    RbdHeader1 *header;
    char *hbuf = NULL;
    char *outbuf = NULL, *end, *buf;
    uint64_t len;
    uint64_t snap_seq;
    uint32_t snap_count;
    int r, i;

    /* read header to estimate how much space we need to read the snap
     * list */
    if ((r = rbd_read_header(s, &hbuf)) < 0) {
        goto done_err;
    }
    header = (RbdHeader1 *)hbuf;
    len = le64_to_cpu(header->snap_names_len);
    len += 1024; /* should have already been enough, but new snapshots might
                    already been created since we read the header. just allocate
                    a bit more, so that in most cases it'll suffice anyway */
    qemu_free(hbuf);

    snprintf(n, sizeof(n), "%s%s", s->name, RBD_SUFFIX);
    while (1) {
        qemu_free(outbuf);
        outbuf = qemu_malloc(len);

        r = rados_exec(s->header_pool, n, "rbd", "snap_list", NULL, 0,
                       outbuf, len);
        if (r < 0) {
            error_report("rbd.snap_list execution failed failed: %s", strerror(-r));
            goto done_err;
        }
        if (r != len) {
            break;
	}

        /* if we're here, we probably raced with some snaps creation */
        len *= 2;
    }
    buf = outbuf;
    end = buf + len;

    if ((r = decode64(&buf, end, &snap_seq)) < 0) {
        goto done_err;
    }
    if ((r = decode32(&buf, end, &snap_count)) < 0) {
        goto done_err;
    }

    sn_tab = qemu_mallocz(snap_count * sizeof(QEMUSnapshotInfo));
    for (i = 0; i < snap_count; i++) {
        uint64_t id, image_size;
        char *snap_name;

        if ((r = decode64(&buf, end, &id)) < 0) {
            goto done_err;
        }
        if ((r = decode64(&buf, end, &image_size)) < 0) {
            goto done_err;
        }
        if ((r = decode_str(&buf, end, &snap_name)) < 0) {
            goto done_err;
        }

        sn_info = sn_tab + i;
        pstrcpy(sn_info->id_str, sizeof(sn_info->id_str), snap_name);
        pstrcpy(sn_info->name, sizeof(sn_info->name), snap_name);
        qemu_free(snap_name);

        sn_info->vm_state_size = image_size;
        sn_info->date_sec = 0;
        sn_info->date_nsec = 0;
        sn_info->vm_clock_nsec = 0;
    }
    *psn_tab = sn_tab;
    qemu_free(outbuf);
    return snap_count;
done_err:
    qemu_free(sn_tab);
    qemu_free(outbuf);
    return r;
}

static QEMUOptionParameter rbd_create_options[] = {
    {
     .name = BLOCK_OPT_SIZE,
     .type = OPT_SIZE,
     .help = "Virtual disk size"
    },
    {
     .name = BLOCK_OPT_CLUSTER_SIZE,
     .type = OPT_SIZE,
     .help = "RBD object size"
    },
    {NULL}
};

static BlockDriver bdrv_rbd = {
    .format_name        = "rbd",
    .instance_size      = sizeof(BDRVRBDState),
    .bdrv_file_open     = rbd_open,
    .bdrv_close         = rbd_close,
    .bdrv_create        = rbd_create,
    .bdrv_get_info      = rbd_getinfo,
    .create_options     = rbd_create_options,
    .bdrv_getlength     = rbd_getlength,
    .protocol_name      = "rbd",

    .bdrv_aio_readv     = rbd_aio_readv,
    .bdrv_aio_writev    = rbd_aio_writev,

    .bdrv_snapshot_create = rbd_snap_create,
    .bdrv_snapshot_list = rbd_snap_list,
};

static void bdrv_rbd_init(void)
{
    bdrv_register(&bdrv_rbd);
}

block_init(bdrv_rbd_init);