Archipelago » qemu

/*

 * QEMU Block driver for RADOS (Ceph)

 *

 * Copyright (C) 2010-2011 Christian Brunner <chb@muc.de>,

 *                         Josh Durgin <josh.durgin@dreamhost.com>

 *

 * This work is licensed under the terms of the GNU GPL, version 2.  See

 * the COPYING file in the top-level directory.

 *

 * Contributions after 2012-01-13 are licensed under the terms of the

 * GNU GPL, version 2 or (at your option) any later version.

 */

#include <inttypes.h>

#include "qemu-common.h"

#include "qemu/error-report.h"

#include "block/block_int.h"

#include <rbd/librbd.h>

/*

 * When specifying the image filename use:

 *

 * rbd:poolname/devicename[@snapshotname][:option1=value1[:option2=value2...]]

 *

 * poolname must be the name of an existing rados pool.

 *

 * devicename is the name of the rbd image.

 *

 * Each option given is used to configure rados, and may be any valid

 * Ceph option, "id", or "conf".

 *

 * The "id" option indicates what user we should authenticate as to

 * the Ceph cluster.  If it is excluded we will use the Ceph default

 * (normally 'admin').

 *

 * The "conf" option specifies a Ceph configuration file to read.  If

 * it is not specified, we will read from the default Ceph locations

 * (e.g., /etc/ceph/ceph.conf).  To avoid reading _any_ configuration

 * file, specify conf=/dev/null.

 *

 * Configuration values containing :, @, or = can be escaped with a

 * leading "\".

 */

/* rbd_aio_discard added in 0.1.2 */

#if LIBRBD_VERSION_CODE >= LIBRBD_VERSION(0, 1, 2)

#define LIBRBD_SUPPORTS_DISCARD

#else

#undef LIBRBD_SUPPORTS_DISCARD

#endif

#define OBJ_MAX_SIZE (1UL << OBJ_DEFAULT_OBJ_ORDER)

#define RBD_MAX_CONF_NAME_SIZE 128

#define RBD_MAX_CONF_VAL_SIZE 512

#define RBD_MAX_CONF_SIZE 1024

#define RBD_MAX_POOL_NAME_SIZE 128

#define RBD_MAX_SNAP_NAME_SIZE 128

#define RBD_MAX_SNAPS 100

typedef enum {

    RBD_AIO_READ,

    RBD_AIO_WRITE,

    RBD_AIO_DISCARD,

    RBD_AIO_FLUSH

} RBDAIOCmd;

typedef struct RBDAIOCB {

    BlockDriverAIOCB common;

    QEMUBH *bh;

    int64_t ret;

    QEMUIOVector *qiov;

    char *bounce;

    RBDAIOCmd cmd;

    int64_t sector_num;

    int error;

    struct BDRVRBDState *s;

    int cancelled;

    int status;

} RBDAIOCB;

typedef struct RADOSCB {

    int rcbid;

    RBDAIOCB *acb;

    struct BDRVRBDState *s;

    int done;

    int64_t size;

    char *buf;

    int64_t ret;

} RADOSCB;

#define RBD_FD_READ 0

#define RBD_FD_WRITE 1

typedef struct BDRVRBDState {

    int fds[2];

    rados_t cluster;

    rados_ioctx_t io_ctx;

    rbd_image_t image;

    char name[RBD_MAX_IMAGE_NAME_SIZE];

    char *snap;

    int event_reader_pos;

    RADOSCB *event_rcb;

} BDRVRBDState;

static void rbd_aio_bh_cb(void *opaque);

static int qemu_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') {

        for (end = src; *end; ++end) {

            if (*end == delim) {

                break;

            }

            if (*end == '\\' && end[1] != '\0') {

                end++;

            }

        }

        if (*end == delim) {

            *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 void qemu_rbd_unescape(char *src)

{

    char *p;

    for (p = src; *src; ++src, ++p) {

        if (*src == '\\' && src[1] != '\0') {

            src++;

        }

        *p = *src;

    }

    *p = '\0';

}

static int qemu_rbd_parsename(const char *filename,

                              char *pool, int pool_len,

                              char *snap, int snap_len,

                              char *name, int name_len,

                              char *conf, int conf_len)

{

    const char *start;

    char *p, *buf;

    int ret;

    if (!strstart(filename, "rbd:", &start)) {

        return -EINVAL;

    }

    buf = g_strdup(start);

    p = buf;

    *snap = '\0';

    *conf = '\0';

    ret = qemu_rbd_next_tok(pool, pool_len, p, '/', "pool name", &p);

    if (ret < 0 || !p) {

        ret = -EINVAL;

        goto done;

    }

    qemu_rbd_unescape(pool);

    if (strchr(p, '@')) {

        ret = qemu_rbd_next_tok(name, name_len, p, '@', "object name", &p);

        if (ret < 0) {

            goto done;

        }

        ret = qemu_rbd_next_tok(snap, snap_len, p, ':', "snap name", &p);

        qemu_rbd_unescape(snap);

    } else {

        ret = qemu_rbd_next_tok(name, name_len, p, ':', "object name", &p);

    }

    qemu_rbd_unescape(name);

    if (ret < 0 || !p) {

        goto done;

    }

    ret = qemu_rbd_next_tok(conf, conf_len, p, '\0', "configuration", &p);

done:

    g_free(buf);

    return ret;

}

static char *qemu_rbd_parse_clientname(const char *conf, char *clientname)

{

    const char *p = conf;

    while (*p) {

        int len;

        const char *end = strchr(p, ':');

        if (end) {

            len = end - p;

        } else {

            len = strlen(p);

        }

        if (strncmp(p, "id=", 3) == 0) {

            len -= 3;

            strncpy(clientname, p + 3, len);

            clientname[len] = '\0';

            return clientname;

        }

        if (end == NULL) {

            break;

        }

        p = end + 1;

    }

    return NULL;

}

static int qemu_rbd_set_conf(rados_t cluster, const char *conf)

{

    char *p, *buf;

    char name[RBD_MAX_CONF_NAME_SIZE];

    char value[RBD_MAX_CONF_VAL_SIZE];

    int ret = 0;

    buf = g_strdup(conf);

    p = buf;

    while (p) {

        ret = qemu_rbd_next_tok(name, sizeof(name), p,

                                '=', "conf option name", &p);

        if (ret < 0) {

            break;

        }

        qemu_rbd_unescape(name);

        if (!p) {

            error_report("conf option %s has no value", name);

            ret = -EINVAL;

            break;

        }

        ret = qemu_rbd_next_tok(value, sizeof(value), p,

                                ':', "conf option value", &p);

        if (ret < 0) {

            break;

        }

        qemu_rbd_unescape(value);

        if (strcmp(name, "conf") == 0) {

            ret = rados_conf_read_file(cluster, value);

            if (ret < 0) {

                error_report("error reading conf file %s", value);

                break;

            }

        } else if (strcmp(name, "id") == 0) {

            /* ignore, this is parsed by qemu_rbd_parse_clientname() */

        } else {

            ret = rados_conf_set(cluster, name, value);

            if (ret < 0) {

                error_report("invalid conf option %s", name);

                ret = -EINVAL;

                break;

            }

        }

    }

    g_free(buf);

    return ret;

}

static int qemu_rbd_create(const char *filename, QEMUOptionParameter *options)

{

    int64_t bytes = 0;

    int64_t objsize;

    int obj_order = 0;

    char pool[RBD_MAX_POOL_NAME_SIZE];

    char name[RBD_MAX_IMAGE_NAME_SIZE];

    char snap_buf[RBD_MAX_SNAP_NAME_SIZE];

    char conf[RBD_MAX_CONF_SIZE];

    char clientname_buf[RBD_MAX_CONF_SIZE];

    char *clientname;

    rados_t cluster;

    rados_ioctx_t io_ctx;

    int ret;

    if (qemu_rbd_parsename(filename, pool, sizeof(pool),

                           snap_buf, sizeof(snap_buf),

                           name, sizeof(name),

                           conf, sizeof(conf)) < 0) {

        return -EINVAL;

    }

    /* 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++;

    }

    clientname = qemu_rbd_parse_clientname(conf, clientname_buf);

    if (rados_create(&cluster, clientname) < 0) {

        error_report("error initializing");

        return -EIO;

    }

    if (strstr(conf, "conf=") == NULL) {

        /* try default location, but ignore failure */

        rados_conf_read_file(cluster, NULL);

    }

    if (conf[0] != '\0' &&

        qemu_rbd_set_conf(cluster, conf) < 0) {

        error_report("error setting config options");

        rados_shutdown(cluster);

        return -EIO;

    }

    if (rados_connect(cluster) < 0) {

        error_report("error connecting");

        rados_shutdown(cluster);

        return -EIO;

    }

    if (rados_ioctx_create(cluster, pool, &io_ctx) < 0) {

        error_report("error opening pool %s", pool);

        rados_shutdown(cluster);

        return -EIO;

    }

    ret = rbd_create(io_ctx, name, bytes, &obj_order);

    rados_ioctx_destroy(io_ctx);

    rados_shutdown(cluster);

    return ret;

}

/*

 * This aio completion is being called from qemu_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 qemu_rbd_complete_aio(RADOSCB *rcb)

{

    RBDAIOCB *acb = rcb->acb;

    int64_t r;

    r = rcb->ret;

    if (acb->cmd != RBD_AIO_READ) {

        if (r < 0) {

            acb->ret = r;

            acb->error = 1;

        } else if (!acb->error) {

            acb->ret = rcb->size;

        }

    } else {

        if (r < 0) {

            memset(rcb->buf, 0, rcb->size);

            acb->ret = r;

            acb->error = 1;

        } else if (r < rcb->size) {

            memset(rcb->buf + r, 0, rcb->size - r);

            if (!acb->error) {

                acb->ret = rcb->size;

            }

        } else if (!acb->error) {

            acb->ret = r;

        }

    }

    /* Note that acb->bh can be NULL in case where the aio was cancelled */

    acb->bh = qemu_bh_new(rbd_aio_bh_cb, acb);

    qemu_bh_schedule(acb->bh);

    g_free(rcb);

}

/*

 * aio fd read handler. It runs in the qemu context and calls the

 * completion handling of completed rados aio operations.

 */

static void qemu_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 */

        ret = read(s->fds[RBD_FD_READ], p + s->event_reader_pos,

                   sizeof(s->event_rcb) - s->event_reader_pos);

        if (ret > 0) {

            s->event_reader_pos += ret;

            if (s->event_reader_pos == sizeof(s->event_rcb)) {

                s->event_reader_pos = 0;

                qemu_rbd_complete_aio(s->event_rcb);

            }

        }

    } while (ret < 0 && errno == EINTR);

}

/* TODO Convert to fine grained options */

static QemuOptsList runtime_opts = {

    .name = "rbd",

    .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),

    .desc = {

        {

            .name = "filename",

            .type = QEMU_OPT_STRING,

            .help = "Specification of the rbd image",

        },

        { /* end of list */ }

    },

};

static int qemu_rbd_open(BlockDriverState *bs, QDict *options, int flags)

{

    BDRVRBDState *s = bs->opaque;

    char pool[RBD_MAX_POOL_NAME_SIZE];

    char snap_buf[RBD_MAX_SNAP_NAME_SIZE];

    char conf[RBD_MAX_CONF_SIZE];

    char clientname_buf[RBD_MAX_CONF_SIZE];

    char *clientname;

    QemuOpts *opts;

    Error *local_err = NULL;

    const char *filename;

    int r;

    opts = qemu_opts_create_nofail(&runtime_opts);

    qemu_opts_absorb_qdict(opts, options, &local_err);

    if (error_is_set(&local_err)) {

        qerror_report_err(local_err);

        error_free(local_err);

        qemu_opts_del(opts);

        return -EINVAL;

    }

    filename = qemu_opt_get(opts, "filename");

    if (qemu_rbd_parsename(filename, pool, sizeof(pool),

                           snap_buf, sizeof(snap_buf),

                           s->name, sizeof(s->name),

                           conf, sizeof(conf)) < 0) {

        r = -EINVAL;

        goto failed_opts;

    }

    clientname = qemu_rbd_parse_clientname(conf, clientname_buf);

    r = rados_create(&s->cluster, clientname);

    if (r < 0) {

        error_report("error initializing");

        goto failed_opts;

    }

    s->snap = NULL;

    if (snap_buf[0] != '\0') {

        s->snap = g_strdup(snap_buf);

    }

    /*

     * Fallback to more conservative semantics if setting cache

     * options fails. Ignore errors from setting rbd_cache because the

     * only possible error is that the option does not exist, and

     * librbd defaults to no caching. If write through caching cannot

     * be set up, fall back to no caching.

     */

    if (flags & BDRV_O_NOCACHE) {

        rados_conf_set(s->cluster, "rbd_cache", "false");

    } else {

        rados_conf_set(s->cluster, "rbd_cache", "true");

    }

    if (strstr(conf, "conf=") == NULL) {

        /* try default location, but ignore failure */

        rados_conf_read_file(s->cluster, NULL);

    }

    if (conf[0] != '\0') {

        r = qemu_rbd_set_conf(s->cluster, conf);

        if (r < 0) {

            error_report("error setting config options");

            goto failed_shutdown;

        }

    }

    r = rados_connect(s->cluster);

    if (r < 0) {

        error_report("error connecting");

        goto failed_shutdown;

    }

    r = rados_ioctx_create(s->cluster, pool, &s->io_ctx);

    if (r < 0) {

        error_report("error opening pool %s", pool);

        goto failed_shutdown;

    }

    r = rbd_open(s->io_ctx, s->name, &s->image, s->snap);

    if (r < 0) {

        error_report("error reading header from %s", s->name);

        goto failed_open;

    }

    bs->read_only = (s->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], qemu_rbd_aio_event_reader,

                            NULL, s);

    qemu_opts_del(opts);

    return 0;

failed:

    rbd_close(s->image);

failed_open:

    rados_ioctx_destroy(s->io_ctx);

failed_shutdown:

    rados_shutdown(s->cluster);

    g_free(s->snap);

failed_opts:

    qemu_opts_del(opts);

    return r;

}

static void qemu_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);

    rbd_close(s->image);

    rados_ioctx_destroy(s->io_ctx);

    g_free(s->snap);

    rados_shutdown(s->cluster);

}

/*

 * Cancel aio. Since we don't reference acb in a non qemu threads,

 * it is safe to access it here.

 */

static void qemu_rbd_aio_cancel(BlockDriverAIOCB *blockacb)

{

    RBDAIOCB *acb = (RBDAIOCB *) blockacb;

    acb->cancelled = 1;

    while (acb->status == -EINPROGRESS) {

        qemu_aio_wait();

    }

    qemu_aio_release(acb);

}

static const AIOCBInfo rbd_aiocb_info = {

    .aiocb_size = sizeof(RBDAIOCB),

    .cancel = qemu_rbd_aio_cancel,

};

static int qemu_rbd_send_pipe(BDRVRBDState *s, RADOSCB *rcb)

{

    int ret = 0;

    while (1) {

        fd_set wfd;

        int fd = s->fds[RBD_FD_WRITE];

        /* send the op pointer to the qemu thread that is responsible

           for the aio/op 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);

    }

    return ret;

}

/*

 * This is the callback function for rbd_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 qemu_rbd_aio_event_reader() which

 * runs in a qemu context.

 */

static void rbd_finish_aiocb(rbd_completion_t c, RADOSCB *rcb)

{

    int ret;

    rcb->ret = rbd_aio_get_return_value(c);

    rbd_aio_release(c);

    ret = qemu_rbd_send_pipe(rcb->s, rcb);

    if (ret < 0) {

        error_report("failed writing to acb->s->fds");

        g_free(rcb);

    }

}

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

static void rbd_aio_bh_cb(void *opaque)

{

    RBDAIOCB *acb = opaque;

    if (acb->cmd == RBD_AIO_READ) {

        qemu_iovec_from_buf(acb->qiov, 0, 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;

    acb->status = 0;

    if (!acb->cancelled) {

        qemu_aio_release(acb);

    }

}

static int rbd_aio_discard_wrapper(rbd_image_t image,

                                   uint64_t off,

                                   uint64_t len,

                                   rbd_completion_t comp)

{

#ifdef LIBRBD_SUPPORTS_DISCARD

    return rbd_aio_discard(image, off, len, comp);

#else

    return -ENOTSUP;

#endif

}

static int rbd_aio_flush_wrapper(rbd_image_t image,

                                 rbd_completion_t comp)

{

#ifdef LIBRBD_SUPPORTS_AIO_FLUSH

    return rbd_aio_flush(image, comp);

#else

    return -ENOTSUP;

#endif

}

static BlockDriverAIOCB *rbd_start_aio(BlockDriverState *bs,

                                       int64_t sector_num,

                                       QEMUIOVector *qiov,

                                       int nb_sectors,

                                       BlockDriverCompletionFunc *cb,

                                       void *opaque,

                                       RBDAIOCmd cmd)

{

    RBDAIOCB *acb;

    RADOSCB *rcb;

    rbd_completion_t c;

    int64_t off, size;

    char *buf;

    int r;

    BDRVRBDState *s = bs->opaque;

    acb = qemu_aio_get(&rbd_aiocb_info, bs, cb, opaque);

    acb->cmd = cmd;

    acb->qiov = qiov;

    if (cmd == RBD_AIO_DISCARD || cmd == RBD_AIO_FLUSH) {

        acb->bounce = NULL;

    } else {

        acb->bounce = qemu_blockalign(bs, qiov->size);

    }

    acb->ret = 0;

    acb->error = 0;

    acb->s = s;

    acb->cancelled = 0;

    acb->bh = NULL;

    acb->status = -EINPROGRESS;

    if (cmd == RBD_AIO_WRITE) {

        qemu_iovec_to_buf(acb->qiov, 0, acb->bounce, qiov->size);

    }

    buf = acb->bounce;

    off = sector_num * BDRV_SECTOR_SIZE;

    size = nb_sectors * BDRV_SECTOR_SIZE;

    rcb = g_malloc(sizeof(RADOSCB));

    rcb->done = 0;

    rcb->acb = acb;

    rcb->buf = buf;

    rcb->s = acb->s;

    rcb->size = size;

    r = rbd_aio_create_completion(rcb, (rbd_callback_t) rbd_finish_aiocb, &c);

    if (r < 0) {

        goto failed;

    }

    switch (cmd) {

    case RBD_AIO_WRITE:

        r = rbd_aio_write(s->image, off, size, buf, c);

        break;

    case RBD_AIO_READ:

        r = rbd_aio_read(s->image, off, size, buf, c);

        break;

    case RBD_AIO_DISCARD:

        r = rbd_aio_discard_wrapper(s->image, off, size, c);

        break;

    case RBD_AIO_FLUSH:

        r = rbd_aio_flush_wrapper(s->image, c);

        break;

    default:

        r = -EINVAL;

    }

    if (r < 0) {

        goto failed;

    }

    return &acb->common;

failed:

    g_free(rcb);

    qemu_aio_release(acb);

    return NULL;

}

static BlockDriverAIOCB *qemu_rbd_aio_readv(BlockDriverState *bs,

                                            int64_t sector_num,

                                            QEMUIOVector *qiov,

                                            int nb_sectors,

                                            BlockDriverCompletionFunc *cb,

                                            void *opaque)

{

    return rbd_start_aio(bs, sector_num, qiov, nb_sectors, cb, opaque,

                         RBD_AIO_READ);

}

static BlockDriverAIOCB *qemu_rbd_aio_writev(BlockDriverState *bs,

                                             int64_t sector_num,

                                             QEMUIOVector *qiov,

                                             int nb_sectors,

                                             BlockDriverCompletionFunc *cb,

                                             void *opaque)

{

    return rbd_start_aio(bs, sector_num, qiov, nb_sectors, cb, opaque,

                         RBD_AIO_WRITE);

}

#ifdef LIBRBD_SUPPORTS_AIO_FLUSH

static BlockDriverAIOCB *qemu_rbd_aio_flush(BlockDriverState *bs,

                                            BlockDriverCompletionFunc *cb,

                                            void *opaque)

{

    return rbd_start_aio(bs, 0, NULL, 0, cb, opaque, RBD_AIO_FLUSH);

}

#else

static int qemu_rbd_co_flush(BlockDriverState *bs)

{

#if LIBRBD_VERSION_CODE >= LIBRBD_VERSION(0, 1, 1)

    /* rbd_flush added in 0.1.1 */

    BDRVRBDState *s = bs->opaque;

    return rbd_flush(s->image);

#else

    return 0;

#endif

}

#endif

static int qemu_rbd_getinfo(BlockDriverState *bs, BlockDriverInfo *bdi)

{

    BDRVRBDState *s = bs->opaque;

    rbd_image_info_t info;

    int r;

    r = rbd_stat(s->image, &info, sizeof(info));

    if (r < 0) {

        return r;

    }

    bdi->cluster_size = info.obj_size;

    return 0;

}

static int64_t qemu_rbd_getlength(BlockDriverState *bs)

{

    BDRVRBDState *s = bs->opaque;

    rbd_image_info_t info;

    int r;

    r = rbd_stat(s->image, &info, sizeof(info));

    if (r < 0) {

        return r;

    }

    return info.size;

}

static int qemu_rbd_truncate(BlockDriverState *bs, int64_t offset)

{

    BDRVRBDState *s = bs->opaque;

    int r;

    r = rbd_resize(s->image, offset);

    if (r < 0) {

        return r;

    }

    return 0;

}

static int qemu_rbd_snap_create(BlockDriverState *bs,

                                QEMUSnapshotInfo *sn_info)

{

    BDRVRBDState *s = bs->opaque;

    int r;

    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 = rbd_snap_create(s->image, sn_info->name);

    if (r < 0) {

        error_report("failed to create snap: %s", strerror(-r));

        return r;

    }

    return 0;

}

static int qemu_rbd_snap_remove(BlockDriverState *bs,

                                const char *snapshot_name)