qemu/block/gluster.c

/*
 * GlusterFS backend for QEMU
 *
 * Copyright (C) 2012 Bharata B Rao <bharata@linux.vnet.ibm.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or later.
 * See the COPYING file in the top-level directory.
 *
 */
#include "qemu/osdep.h"
#include <glusterfs/api/glfs.h>
#include "block/block_int.h"
#include "qapi/error.h"
#include "qemu/uri.h"
#include "qemu/error-report.h"

#define GLUSTER_OPT_FILENAME        "filename"
#define GLUSTER_OPT_DEBUG           "debug"
#define GLUSTER_DEBUG_DEFAULT       4
#define GLUSTER_DEBUG_MAX           9


typedef struct GlusterAIOCB {
    int64_t size;
    int ret;
    QEMUBH *bh;
    Coroutine *coroutine;
    AioContext *aio_context;
} GlusterAIOCB;

typedef struct BDRVGlusterState {
    struct glfs *glfs;
    struct glfs_fd *fd;
    bool supports_seek_data;
    int debug_level;
} BDRVGlusterState;

typedef struct BDRVGlusterReopenState {
    struct glfs *glfs;
    struct glfs_fd *fd;
} BDRVGlusterReopenState;

typedef struct GlusterConf {
    char *host;
    int port;
    char *volume;
    char *path;
    char *transport;
    int debug_level;
} GlusterConf;


static QemuOptsList qemu_gluster_create_opts = {
    .name = "qemu-gluster-create-opts",
    .head = QTAILQ_HEAD_INITIALIZER(qemu_gluster_create_opts.head),
    .desc = {
        {
            .name = BLOCK_OPT_SIZE,
            .type = QEMU_OPT_SIZE,
            .help = "Virtual disk size"
        },
        {
            .name = BLOCK_OPT_PREALLOC,
            .type = QEMU_OPT_STRING,
            .help = "Preallocation mode (allowed values: off, full)"
        },
        {
            .name = GLUSTER_OPT_DEBUG,
            .type = QEMU_OPT_NUMBER,
            .help = "Gluster log level, valid range is 0-9",
        },
        { /* end of list */ }
    }
};

static QemuOptsList runtime_opts = {
    .name = "gluster",
    .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
    .desc = {
        {
            .name = GLUSTER_OPT_FILENAME,
            .type = QEMU_OPT_STRING,
            .help = "URL to the gluster image",
        },
        {
            .name = GLUSTER_OPT_DEBUG,
            .type = QEMU_OPT_NUMBER,
            .help = "Gluster log level, valid range is 0-9",
        },
        { /* end of list */ }
    },
};


static void qemu_gluster_gconf_free(GlusterConf *gconf)
{
    if (gconf) {
        g_free(gconf->host);
        g_free(gconf->volume);
        g_free(gconf->path);
        g_free(gconf->transport);
        g_free(gconf);
    }
}

static int parse_volume_options(GlusterConf *gconf, char *path)
{
    char *p, *q;

    if (!path) {
        return -EINVAL;
    }

    /* volume */
    p = q = path + strspn(path, "/");
    p += strcspn(p, "/");
    if (*p == '\0') {
        return -EINVAL;
    }
    gconf->volume = g_strndup(q, p - q);

    /* path */
    p += strspn(p, "/");
    if (*p == '\0') {
        return -EINVAL;
    }
    gconf->path = g_strdup(p);
    return 0;
}

/*
 * file=gluster[+transport]://[host[:port]]/volume/path[?socket=...]
 *
 * 'gluster' is the protocol.
 *
 * 'transport' specifies the transport type used to connect to gluster
 * management daemon (glusterd). Valid transport types are
 * tcp or unix. If a transport type isn't specified, then tcp type is assumed.
 *
 * 'host' specifies the host where the volume file specification for
 * the given volume resides. This can be either hostname or ipv4 address.
 * If transport type is 'unix', then 'host' field should not be specified.
 * The 'socket' field needs to be populated with the path to unix domain
 * socket.
 *
 * 'port' is the port number on which glusterd is listening. This is optional
 * and if not specified, QEMU will send 0 which will make gluster to use the
 * default port. If the transport type is unix, then 'port' should not be
 * specified.
 *
 * 'volume' is the name of the gluster volume which contains the VM image.
 *
 * 'path' is the path to the actual VM image that resides on gluster volume.
 *
 * Examples:
 *
 * file=gluster://1.2.3.4/testvol/a.img
 * file=gluster+tcp://1.2.3.4/testvol/a.img
 * file=gluster+tcp://1.2.3.4:24007/testvol/dir/a.img
 * file=gluster+tcp://host.domain.com:24007/testvol/dir/a.img
 * file=gluster+unix:///testvol/dir/a.img?socket=/tmp/glusterd.socket
 */
static int qemu_gluster_parseuri(GlusterConf *gconf, const char *filename)
{
    URI *uri;
    QueryParams *qp = NULL;
    bool is_unix = false;
    int ret = 0;

    uri = uri_parse(filename);
    if (!uri) {
        return -EINVAL;
    }

    /* transport */
    if (!uri->scheme || !strcmp(uri->scheme, "gluster")) {
        gconf->transport = g_strdup("tcp");
    } else if (!strcmp(uri->scheme, "gluster+tcp")) {
        gconf->transport = g_strdup("tcp");
    } else if (!strcmp(uri->scheme, "gluster+unix")) {
        gconf->transport = g_strdup("unix");
        is_unix = true;
    } else if (!strcmp(uri->scheme, "gluster+rdma")) {
        gconf->transport = g_strdup("tcp");
        error_report("Warning: rdma feature is not supported, falling "
                     "back to tcp");
    } else {
        ret = -EINVAL;
        goto out;
    }

    ret = parse_volume_options(gconf, uri->path);
    if (ret < 0) {
        goto out;
    }

    qp = query_params_parse(uri->query);
    if (qp->n > 1 || (is_unix && !qp->n) || (!is_unix && qp->n)) {
        ret = -EINVAL;
        goto out;
    }

    if (is_unix) {
        if (uri->server || uri->port) {
            ret = -EINVAL;
            goto out;
        }
        if (strcmp(qp->p[0].name, "socket")) {
            ret = -EINVAL;
            goto out;
        }
        gconf->host = g_strdup(qp->p[0].value);
    } else {
        gconf->host = g_strdup(uri->server ? uri->server : "localhost");
        gconf->port = uri->port;
    }

out:
    if (qp) {
        query_params_free(qp);
    }
    uri_free(uri);
    return ret;
}

static struct glfs *qemu_gluster_init(GlusterConf *gconf, const char *filename,
                                      Error **errp)
{
    struct glfs *glfs = NULL;
    int ret;
    int old_errno;

    ret = qemu_gluster_parseuri(gconf, filename);
    if (ret < 0) {
        error_setg(errp, "Usage: file=gluster[+transport]://[host[:port]]/"
                         "volume/path[?socket=...]");
        errno = -ret;
        goto out;
    }

    glfs = glfs_new(gconf->volume);
    if (!glfs) {
        goto out;
    }

    ret = glfs_set_volfile_server(glfs, gconf->transport, gconf->host,
            gconf->port);
    if (ret < 0) {
        goto out;
    }

    ret = glfs_set_logging(glfs, "-", gconf->debug_level);
    if (ret < 0) {
        goto out;
    }

    ret = glfs_init(glfs);
    if (ret) {
        error_setg_errno(errp, errno,
                         "Gluster connection failed for host=%s port=%d "
                         "volume=%s path=%s transport=%s", gconf->host,
                         gconf->port, gconf->volume, gconf->path,
                         gconf->transport);

        /* glfs_init sometimes doesn't set errno although docs suggest that */
        if (errno == 0)
            errno = EINVAL;

        goto out;
    }
    return glfs;

out:
    if (glfs) {
        old_errno = errno;
        glfs_fini(glfs);
        errno = old_errno;
    }
    return NULL;
}

static void qemu_gluster_complete_aio(void *opaque)
{
    GlusterAIOCB *acb = (GlusterAIOCB *)opaque;

    qemu_bh_delete(acb->bh);
    acb->bh = NULL;
    qemu_coroutine_enter(acb->coroutine);
}

/*
 * AIO callback routine called from GlusterFS thread.
 */
static void gluster_finish_aiocb(struct glfs_fd *fd, ssize_t ret, void *arg)
{
    GlusterAIOCB *acb = (GlusterAIOCB *)arg;

    if (!ret || ret == acb->size) {
        acb->ret = 0; /* Success */
    } else if (ret < 0) {
        acb->ret = -errno; /* Read/Write failed */
    } else {
        acb->ret = -EIO; /* Partial read/write - fail it */
    }

    acb->bh = aio_bh_new(acb->aio_context, qemu_gluster_complete_aio, acb);
    qemu_bh_schedule(acb->bh);
}

static void qemu_gluster_parse_flags(int bdrv_flags, int *open_flags)
{
    assert(open_flags != NULL);

    *open_flags |= O_BINARY;

    if (bdrv_flags & BDRV_O_RDWR) {
        *open_flags |= O_RDWR;
    } else {
        *open_flags |= O_RDONLY;
    }

    if ((bdrv_flags & BDRV_O_NOCACHE)) {
        *open_flags |= O_DIRECT;
    }
}

/*
 * Do SEEK_DATA/HOLE to detect if it is functional. Older broken versions of
 * gfapi incorrectly return the current offset when SEEK_DATA/HOLE is used.
 * - Corrected versions return -1 and set errno to EINVAL.
 * - Versions that support SEEK_DATA/HOLE correctly, will return -1 and set
 *   errno to ENXIO when SEEK_DATA is called with a position of EOF.
 */
static bool qemu_gluster_test_seek(struct glfs_fd *fd)
{
    off_t ret, eof;

    eof = glfs_lseek(fd, 0, SEEK_END);
    if (eof < 0) {
        /* this should never occur */
        return false;
    }

    /* this should always fail with ENXIO if SEEK_DATA is supported */
    ret = glfs_lseek(fd, eof, SEEK_DATA);
    return (ret < 0) && (errno == ENXIO);
}

static int qemu_gluster_open(BlockDriverState *bs,  QDict *options,
                             int bdrv_flags, Error **errp)
{
    BDRVGlusterState *s = bs->opaque;
    int open_flags = 0;
    int ret = 0;
    GlusterConf *gconf = g_new0(GlusterConf, 1);
    QemuOpts *opts;
    Error *local_err = NULL;
    const char *filename;

    opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
    qemu_opts_absorb_qdict(opts, options, &local_err);
    if (local_err) {
        error_propagate(errp, local_err);
        ret = -EINVAL;
        goto out;
    }

    filename = qemu_opt_get(opts, GLUSTER_OPT_FILENAME);

    s->debug_level = qemu_opt_get_number(opts, GLUSTER_OPT_DEBUG,
                                         GLUSTER_DEBUG_DEFAULT);
    if (s->debug_level < 0) {
        s->debug_level = 0;
    } else if (s->debug_level > GLUSTER_DEBUG_MAX) {
        s->debug_level = GLUSTER_DEBUG_MAX;
    }

    gconf->debug_level = s->debug_level;
    s->glfs = qemu_gluster_init(gconf, filename, errp);
    if (!s->glfs) {
        ret = -errno;
        goto out;
    }

#ifdef CONFIG_GLUSTERFS_XLATOR_OPT
    /* Without this, if fsync fails for a recoverable reason (for instance,
     * ENOSPC), gluster will dump its cache, preventing retries.  This means
     * almost certain data loss.  Not all gluster versions support the
     * 'resync-failed-syncs-after-fsync' key value, but there is no way to
     * discover during runtime if it is supported (this api returns success for
     * unknown key/value pairs) */
    ret = glfs_set_xlator_option(s->glfs, "*-write-behind",
                                          "resync-failed-syncs-after-fsync",
                                          "on");
    if (ret < 0) {
        error_setg_errno(errp, errno, "Unable to set xlator key/value pair");
        ret = -errno;
        goto out;
    }
#endif

    qemu_gluster_parse_flags(bdrv_flags, &open_flags);

    s->fd = glfs_open(s->glfs, gconf->path, open_flags);
    if (!s->fd) {
        ret = -errno;
    }

    s->supports_seek_data = qemu_gluster_test_seek(s->fd);

out:
    qemu_opts_del(opts);
    qemu_gluster_gconf_free(gconf);
    if (!ret) {
        return ret;
    }
    if (s->fd) {
        glfs_close(s->fd);
    }
    if (s->glfs) {
        glfs_fini(s->glfs);
    }
    return ret;
}

static int qemu_gluster_reopen_prepare(BDRVReopenState *state,
                                       BlockReopenQueue *queue, Error **errp)
{
    int ret = 0;
    BDRVGlusterState *s;
    BDRVGlusterReopenState *reop_s;
    GlusterConf *gconf = NULL;
    int open_flags = 0;

    assert(state != NULL);
    assert(state->bs != NULL);

    s = state->bs->opaque;

    state->opaque = g_new0(BDRVGlusterReopenState, 1);
    reop_s = state->opaque;

    qemu_gluster_parse_flags(state->flags, &open_flags);

    gconf = g_new0(GlusterConf, 1);

    gconf->debug_level = s->debug_level;
    reop_s->glfs = qemu_gluster_init(gconf, state->bs->filename, errp);
    if (reop_s->glfs == NULL) {
        ret = -errno;
        goto exit;
    }

#ifdef CONFIG_GLUSTERFS_XLATOR_OPT
    ret = glfs_set_xlator_option(reop_s->glfs, "*-write-behind",
                                 "resync-failed-syncs-after-fsync", "on");
    if (ret < 0) {
        error_setg_errno(errp, errno, "Unable to set xlator key/value pair");
        ret = -errno;
        goto exit;
    }
#endif

    reop_s->fd = glfs_open(reop_s->glfs, gconf->path, open_flags);
    if (reop_s->fd == NULL) {
        /* reops->glfs will be cleaned up in _abort */
        ret = -errno;
        goto exit;
    }

exit:
    /* state->opaque will be freed in either the _abort or _commit */
    qemu_gluster_gconf_free(gconf);
    return ret;
}

static void qemu_gluster_reopen_commit(BDRVReopenState *state)
{
    BDRVGlusterReopenState *reop_s = state->opaque;
    BDRVGlusterState *s = state->bs->opaque;


    /* close the old */
    if (s->fd) {
        glfs_close(s->fd);
    }
    if (s->glfs) {
        glfs_fini(s->glfs);
    }

    /* use the newly opened image / connection */
    s->fd         = reop_s->fd;
    s->glfs       = reop_s->glfs;

    g_free(state->opaque);
    state->opaque = NULL;

    return;
}


static void qemu_gluster_reopen_abort(BDRVReopenState *state)
{
    BDRVGlusterReopenState *reop_s = state->opaque;

    if (reop_s == NULL) {
        return;
    }

    if (reop_s->fd) {
        glfs_close(reop_s->fd);
    }

    if (reop_s->glfs) {
        glfs_fini(reop_s->glfs);
    }

    g_free(state->opaque);
    state->opaque = NULL;

    return;
}

#ifdef CONFIG_GLUSTERFS_ZEROFILL
static coroutine_fn int qemu_gluster_co_pwrite_zeroes(BlockDriverState *bs,
                                                      int64_t offset,
                                                      int size,
                                                      BdrvRequestFlags flags)
{
    int ret;
    GlusterAIOCB acb;
    BDRVGlusterState *s = bs->opaque;

    acb.size = size;
    acb.ret = 0;
    acb.coroutine = qemu_coroutine_self();
    acb.aio_context = bdrv_get_aio_context(bs);

    ret = glfs_zerofill_async(s->fd, offset, size, gluster_finish_aiocb, &acb);
    if (ret < 0) {
        return -errno;
    }

    qemu_coroutine_yield();
    return acb.ret;
}

static inline bool gluster_supports_zerofill(void)
{
    return 1;
}

static inline int qemu_gluster_zerofill(struct glfs_fd *fd, int64_t offset,
                                        int64_t size)
{
    return glfs_zerofill(fd, offset, size);
}

#else
static inline bool gluster_supports_zerofill(void)
{
    return 0;
}

static inline int qemu_gluster_zerofill(struct glfs_fd *fd, int64_t offset,
                                        int64_t size)
{
    return 0;
}
#endif

static int qemu_gluster_create(const char *filename,
                               QemuOpts *opts, Error **errp)
{
    struct glfs *glfs;
    struct glfs_fd *fd;
    int ret = 0;
    int prealloc = 0;
    int64_t total_size = 0;
    char *tmp = NULL;
    GlusterConf *gconf = g_new0(GlusterConf, 1);

    gconf->debug_level = qemu_opt_get_number_del(opts, GLUSTER_OPT_DEBUG,
                                                 GLUSTER_DEBUG_DEFAULT);
    if (gconf->debug_level < 0) {
        gconf->debug_level = 0;
    } else if (gconf->debug_level > GLUSTER_DEBUG_MAX) {
        gconf->debug_level = GLUSTER_DEBUG_MAX;
    }

    glfs = qemu_gluster_init(gconf, filename, errp);
    if (!glfs) {
        ret = -errno;
        goto out;
    }

    total_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
                          BDRV_SECTOR_SIZE);

    tmp = qemu_opt_get_del(opts, BLOCK_OPT_PREALLOC);
    if (!tmp || !strcmp(tmp, "off")) {
        prealloc = 0;
    } else if (!strcmp(tmp, "full") && gluster_supports_zerofill()) {
        prealloc = 1;
    } else {
        error_setg(errp, "Invalid preallocation mode: '%s'"
                         " or GlusterFS doesn't support zerofill API", tmp);
        ret = -EINVAL;
        goto out;
    }

    fd = glfs_creat(glfs, gconf->path,
                    O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, S_IRUSR | S_IWUSR);
    if (!fd) {
        ret = -errno;
    } else {
        if (!glfs_ftruncate(fd, total_size)) {
            if (prealloc && qemu_gluster_zerofill(fd, 0, total_size)) {
                ret = -errno;
            }
        } else {
            ret = -errno;
        }

        if (glfs_close(fd) != 0) {
            ret = -errno;
        }
    }
out:
    g_free(tmp);
    qemu_gluster_gconf_free(gconf);
    if (glfs) {
        glfs_fini(glfs);
    }
    return ret;
}

static coroutine_fn int qemu_gluster_co_rw(BlockDriverState *bs,
                                           int64_t sector_num, int nb_sectors,
                                           QEMUIOVector *qiov, int write)
{
    int ret;
    GlusterAIOCB acb;
    BDRVGlusterState *s = bs->opaque;
    size_t size = nb_sectors * BDRV_SECTOR_SIZE;
    off_t offset = sector_num * BDRV_SECTOR_SIZE;

    acb.size = size;
    acb.ret = 0;
    acb.coroutine = qemu_coroutine_self();
    acb.aio_context = bdrv_get_aio_context(bs);

    if (write) {
        ret = glfs_pwritev_async(s->fd, qiov->iov, qiov->niov, offset, 0,
                                 gluster_finish_aiocb, &acb);
    } else {
        ret = glfs_preadv_async(s->fd, qiov->iov, qiov->niov, offset, 0,
                                gluster_finish_aiocb, &acb);
    }

    if (ret < 0) {
        return -errno;
    }

    qemu_coroutine_yield();
    return acb.ret;
}

static int qemu_gluster_truncate(BlockDriverState *bs, int64_t offset)
{
    int ret;
    BDRVGlusterState *s = bs->opaque;

    ret = glfs_ftruncate(s->fd, offset);
    if (ret < 0) {
        return -errno;
    }

    return 0;
}

static coroutine_fn int qemu_gluster_co_readv(BlockDriverState *bs,
                                              int64_t sector_num,
                                              int nb_sectors,
                                              QEMUIOVector *qiov)
{
    return qemu_gluster_co_rw(bs, sector_num, nb_sectors, qiov, 0);
}

static coroutine_fn int qemu_gluster_co_writev(BlockDriverState *bs,
                                               int64_t sector_num,
                                               int nb_sectors,
                                               QEMUIOVector *qiov)
{
    return qemu_gluster_co_rw(bs, sector_num, nb_sectors, qiov, 1);
}

static void qemu_gluster_close(BlockDriverState *bs)
{
    BDRVGlusterState *s = bs->opaque;

    if (s->fd) {
        glfs_close(s->fd);
        s->fd = NULL;
    }
    glfs_fini(s->glfs);
}

static coroutine_fn int qemu_gluster_co_flush_to_disk(BlockDriverState *bs)
{
    int ret;
    GlusterAIOCB acb;
    BDRVGlusterState *s = bs->opaque;

    acb.size = 0;
    acb.ret = 0;
    acb.coroutine = qemu_coroutine_self();
    acb.aio_context = bdrv_get_aio_context(bs);

    ret = glfs_fsync_async(s->fd, gluster_finish_aiocb, &acb);
    if (ret < 0) {
        ret = -errno;
        goto error;
    }

    qemu_coroutine_yield();
    if (acb.ret < 0) {
        ret = acb.ret;
        goto error;
    }

    return acb.ret;

error:
    /* Some versions of Gluster (3.5.6 -> 3.5.8?) will not retain its cache
     * after a fsync failure, so we have no way of allowing the guest to safely
     * continue.  Gluster versions prior to 3.5.6 don't retain the cache
     * either, but will invalidate the fd on error, so this is again our only
     * option.
     *
     * The 'resync-failed-syncs-after-fsync' xlator option for the
     * write-behind cache will cause later gluster versions to retain its
     * cache after error, so long as the fd remains open.  However, we
     * currently have no way of knowing if this option is supported.
     *
     * TODO: Once gluster provides a way for us to determine if the option
     * is supported, bypass the closure and setting drv to NULL.  */
    qemu_gluster_close(bs);
    bs->drv = NULL;
    return ret;
}

#ifdef CONFIG_GLUSTERFS_DISCARD
static coroutine_fn int qemu_gluster_co_discard(BlockDriverState *bs,
                                                int64_t sector_num,
                                                int nb_sectors)
{
    int ret;
    GlusterAIOCB acb;
    BDRVGlusterState *s = bs->opaque;
    size_t size = nb_sectors * BDRV_SECTOR_SIZE;
    off_t offset = sector_num * BDRV_SECTOR_SIZE;

    acb.size = 0;
    acb.ret = 0;
    acb.coroutine = qemu_coroutine_self();
    acb.aio_context = bdrv_get_aio_context(bs);

    ret = glfs_discard_async(s->fd, offset, size, gluster_finish_aiocb, &acb);
    if (ret < 0) {
        return -errno;
    }

    qemu_coroutine_yield();
    return acb.ret;
}
#endif

static int64_t qemu_gluster_getlength(BlockDriverState *bs)
{
    BDRVGlusterState *s = bs->opaque;
    int64_t ret;

    ret = glfs_lseek(s->fd, 0, SEEK_END);
    if (ret < 0) {
        return -errno;
    } else {
        return ret;
    }
}

static int64_t qemu_gluster_allocated_file_size(BlockDriverState *bs)
{
    BDRVGlusterState *s = bs->opaque;
    struct stat st;
    int ret;

    ret = glfs_fstat(s->fd, &st);
    if (ret < 0) {
        return -errno;
    } else {
        return st.st_blocks * 512;
    }
}

static int qemu_gluster_has_zero_init(BlockDriverState *bs)
{
    /* GlusterFS volume could be backed by a block device */
    return 0;
}

/*
 * Find allocation range in @bs around offset @start.
 * May change underlying file descriptor's file offset.
 * If @start is not in a hole, store @start in @data, and the
 * beginning of the next hole in @hole, and return 0.
 * If @start is in a non-trailing hole, store @start in @hole and the
 * beginning of the next non-hole in @data, and return 0.
 * If @start is in a trailing hole or beyond EOF, return -ENXIO.
 * If we can't find out, return a negative errno other than -ENXIO.
 *
 * (Shamefully copied from raw-posix.c, only miniscule adaptions.)
 */
static int find_allocation(BlockDriverState *bs, off_t start,
                           off_t *data, off_t *hole)
{
    BDRVGlusterState *s = bs->opaque;
    off_t offs;

    if (!s->supports_seek_data) {
        return -ENOTSUP;
    }

    /*
     * SEEK_DATA cases:
     * D1. offs == start: start is in data
     * D2. offs > start: start is in a hole, next data at offs
     * D3. offs < 0, errno = ENXIO: either start is in a trailing hole
     *                              or start is beyond EOF
     *     If the latter happens, the file has been truncated behind
     *     our back since we opened it.  All bets are off then.
     *     Treating like a trailing hole is simplest.
     * D4. offs < 0, errno != ENXIO: we learned nothing
     */
    offs = glfs_lseek(s->fd, start, SEEK_DATA);
    if (offs < 0) {
        return -errno;          /* D3 or D4 */
    }
    assert(offs >= start);

    if (offs > start) {
        /* D2: in hole, next data at offs */
        *hole = start;
        *data = offs;
        return 0;
    }

    /* D1: in data, end not yet known */

    /*
     * SEEK_HOLE cases:
     * H1. offs == start: start is in a hole
     *     If this happens here, a hole has been dug behind our back
     *     since the previous lseek().
     * H2. offs > start: either start is in data, next hole at offs,
     *                   or start is in trailing hole, EOF at offs
     *     Linux treats trailing holes like any other hole: offs ==
     *     start.  Solaris seeks to EOF instead: offs > start (blech).
     *     If that happens here, a hole has been dug behind our back
     *     since the previous lseek().
     * H3. offs < 0, errno = ENXIO: start is beyond EOF
     *     If this happens, the file has been truncated behind our
     *     back since we opened it.  Treat it like a trailing hole.
     * H4. offs < 0, errno != ENXIO: we learned nothing
     *     Pretend we know nothing at all, i.e. "forget" about D1.
     */
    offs = glfs_lseek(s->fd, start, SEEK_HOLE);
    if (offs < 0) {
        return -errno;          /* D1 and (H3 or H4) */
    }
    assert(offs >= start);

    if (offs > start) {
        /*
         * D1 and H2: either in data, next hole at offs, or it was in
         * data but is now in a trailing hole.  In the latter case,
         * all bets are off.  Treating it as if it there was data all
         * the way to EOF is safe, so simply do that.
         */
        *data = start;
        *hole = offs;
        return 0;
    }

    /* D1 and H1 */
    return -EBUSY;
}

/*
 * Returns the allocation status of the specified sectors.
 *
 * If 'sector_num' is beyond the end of the disk image the return value is 0
 * and 'pnum' is set to 0.
 *
 * '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.  If nb_sectors goes
 * beyond the end of the disk image it will be clamped.
 *
 * (Based on raw_co_get_block_status() from raw-posix.c.)
 */
static int64_t coroutine_fn qemu_gluster_co_get_block_status(
        BlockDriverState *bs, int64_t sector_num, int nb_sectors, int *pnum,
        BlockDriverState **file)
{
    BDRVGlusterState *s = bs->opaque;
    off_t start, data = 0, hole = 0;
    int64_t total_size;
    int ret = -EINVAL;

    if (!s->fd) {
        return ret;
    }

    start = sector_num * BDRV_SECTOR_SIZE;
    total_size = bdrv_getlength(bs);
    if (total_size < 0) {
        return total_size;
    } else if (start >= total_size) {
        *pnum = 0;
        return 0;
    } else if (start + nb_sectors * BDRV_SECTOR_SIZE > total_size) {
        nb_sectors = DIV_ROUND_UP(total_size - start, BDRV_SECTOR_SIZE);
    }

    ret = find_allocation(bs, start, &data, &hole);
    if (ret == -ENXIO) {
        /* Trailing hole */
        *pnum = nb_sectors;
        ret = BDRV_BLOCK_ZERO;
    } else if (ret < 0) {
        /* No info available, so pretend there are no holes */
        *pnum = nb_sectors;
        ret = BDRV_BLOCK_DATA;
    } else if (data == start) {
        /* On a data extent, compute sectors to the end of the extent,
         * possibly including a partial sector at EOF. */
        *pnum = MIN(nb_sectors, DIV_ROUND_UP(hole - start, BDRV_SECTOR_SIZE));
        ret = BDRV_BLOCK_DATA;
    } else {
        /* On a hole, compute sectors to the beginning of the next extent.  */
        assert(hole == start);
        *pnum = MIN(nb_sectors, (data - start) / BDRV_SECTOR_SIZE);
        ret = BDRV_BLOCK_ZERO;
    }

    *file = bs;

    return ret | BDRV_BLOCK_OFFSET_VALID | start;
}


static BlockDriver bdrv_gluster = {
    .format_name                  = "gluster",
    .protocol_name                = "gluster",
    .instance_size                = sizeof(BDRVGlusterState),
    .bdrv_needs_filename          = true,
    .bdrv_file_open               = qemu_gluster_open,
    .bdrv_reopen_prepare          = qemu_gluster_reopen_prepare,
    .bdrv_reopen_commit           = qemu_gluster_reopen_commit,
    .bdrv_reopen_abort            = qemu_gluster_reopen_abort,
    .bdrv_close                   = qemu_gluster_close,
    .bdrv_create                  = qemu_gluster_create,
    .bdrv_getlength               = qemu_gluster_getlength,
    .bdrv_get_allocated_file_size = qemu_gluster_allocated_file_size,
    .bdrv_truncate                = qemu_gluster_truncate,
    .bdrv_co_readv                = qemu_gluster_co_readv,
    .bdrv_co_writev               = qemu_gluster_co_writev,
    .bdrv_co_flush_to_disk        = qemu_gluster_co_flush_to_disk,
    .bdrv_has_zero_init           = qemu_gluster_has_zero_init,
#ifdef CONFIG_GLUSTERFS_DISCARD
    .bdrv_co_discard              = qemu_gluster_co_discard,
#endif
#ifdef CONFIG_GLUSTERFS_ZEROFILL
    .bdrv_co_pwrite_zeroes        = qemu_gluster_co_pwrite_zeroes,
#endif
    .bdrv_co_get_block_status     = qemu_gluster_co_get_block_status,
    .create_opts                  = &qemu_gluster_create_opts,
};

static BlockDriver bdrv_gluster_tcp = {
    .format_name                  = "gluster",
    .protocol_name                = "gluster+tcp",
    .instance_size                = sizeof(BDRVGlusterState),
    .bdrv_needs_filename          = true,
    .bdrv_file_open               = qemu_gluster_open,
    .bdrv_reopen_prepare          = qemu_gluster_reopen_prepare,
    .bdrv_reopen_commit           = qemu_gluster_reopen_commit,
    .bdrv_reopen_abort            = qemu_gluster_reopen_abort,
    .bdrv_close                   = qemu_gluster_close,
    .bdrv_create                  = qemu_gluster_create,
    .bdrv_getlength               = qemu_gluster_getlength,
    .bdrv_get_allocated_file_size = qemu_gluster_allocated_file_size,
    .bdrv_truncate                = qemu_gluster_truncate,
    .bdrv_co_readv                = qemu_gluster_co_readv,
    .bdrv_co_writev               = qemu_gluster_co_writev,
    .bdrv_co_flush_to_disk        = qemu_gluster_co_flush_to_disk,
    .bdrv_has_zero_init           = qemu_gluster_has_zero_init,
#ifdef CONFIG_GLUSTERFS_DISCARD
    .bdrv_co_discard              = qemu_gluster_co_discard,
#endif
#ifdef CONFIG_GLUSTERFS_ZEROFILL
    .bdrv_co_pwrite_zeroes        = qemu_gluster_co_pwrite_zeroes,
#endif
    .bdrv_co_get_block_status     = qemu_gluster_co_get_block_status,
    .create_opts                  = &qemu_gluster_create_opts,
};

static BlockDriver bdrv_gluster_unix = {
    .format_name                  = "gluster",
    .protocol_name                = "gluster+unix",
    .instance_size                = sizeof(BDRVGlusterState),
    .bdrv_needs_filename          = true,
    .bdrv_file_open               = qemu_gluster_open,
    .bdrv_reopen_prepare          = qemu_gluster_reopen_prepare,
    .bdrv_reopen_commit           = qemu_gluster_reopen_commit,
    .bdrv_reopen_abort            = qemu_gluster_reopen_abort,
    .bdrv_close                   = qemu_gluster_close,
    .bdrv_create                  = qemu_gluster_create,
    .bdrv_getlength               = qemu_gluster_getlength,
    .bdrv_get_allocated_file_size = qemu_gluster_allocated_file_size,
    .bdrv_truncate                = qemu_gluster_truncate,
    .bdrv_co_readv                = qemu_gluster_co_readv,
    .bdrv_co_writev               = qemu_gluster_co_writev,
    .bdrv_co_flush_to_disk        = qemu_gluster_co_flush_to_disk,
    .bdrv_has_zero_init           = qemu_gluster_has_zero_init,
#ifdef CONFIG_GLUSTERFS_DISCARD
    .bdrv_co_discard              = qemu_gluster_co_discard,
#endif
#ifdef CONFIG_GLUSTERFS_ZEROFILL
    .bdrv_co_pwrite_zeroes        = qemu_gluster_co_pwrite_zeroes,
#endif
    .bdrv_co_get_block_status     = qemu_gluster_co_get_block_status,
    .create_opts                  = &qemu_gluster_create_opts,
};

/* rdma is deprecated (actually never supported for volfile fetch).
 * Let's maintain it for the protocol compatibility, to make sure things
 * won't break immediately. For now, gluster+rdma will fall back to gluster+tcp
 * protocol with a warning.
 * TODO: remove gluster+rdma interface support
 */
static BlockDriver bdrv_gluster_rdma = {
    .format_name                  = "gluster",
    .protocol_name                = "gluster+rdma",
    .instance_size                = sizeof(BDRVGlusterState),
    .bdrv_needs_filename          = true,
    .bdrv_file_open               = qemu_gluster_open,
    .bdrv_reopen_prepare          = qemu_gluster_reopen_prepare,
    .bdrv_reopen_commit           = qemu_gluster_reopen_commit,
    .bdrv_reopen_abort            = qemu_gluster_reopen_abort,
    .bdrv_close                   = qemu_gluster_close,
    .bdrv_create                  = qemu_gluster_create,
    .bdrv_getlength               = qemu_gluster_getlength,
    .bdrv_get_allocated_file_size = qemu_gluster_allocated_file_size,
    .bdrv_truncate                = qemu_gluster_truncate,
    .bdrv_co_readv                = qemu_gluster_co_readv,
    .bdrv_co_writev               = qemu_gluster_co_writev,
    .bdrv_co_flush_to_disk        = qemu_gluster_co_flush_to_disk,
    .bdrv_has_zero_init           = qemu_gluster_has_zero_init,
#ifdef CONFIG_GLUSTERFS_DISCARD
    .bdrv_co_discard              = qemu_gluster_co_discard,
#endif
#ifdef CONFIG_GLUSTERFS_ZEROFILL
    .bdrv_co_pwrite_zeroes        = qemu_gluster_co_pwrite_zeroes,
#endif
    .bdrv_co_get_block_status     = qemu_gluster_co_get_block_status,
    .create_opts                  = &qemu_gluster_create_opts,
};

static void bdrv_gluster_init(void)
{
    bdrv_register(&bdrv_gluster_rdma);
    bdrv_register(&bdrv_gluster_unix);
    bdrv_register(&bdrv_gluster_tcp);
    bdrv_register(&bdrv_gluster);
}

block_init(bdrv_gluster_init);