Re: [Qemu-devel] [PATCH 1/1] ceph/rbd block driver for qemu-kvm (v2)

[Kevin Wolf]

Am 27.05.2010 21:11, schrieb Christian Brunner:
> This is a block driver for the distributed file system Ceph 
> (http://ceph.newdream.net/). This driver uses librados (which 
> is part of the Ceph server) for direct access to the Ceph object 
> store and is running entirely in userspace. Therefore it is 
> called "rbd" - rados block device.
> 
> To compile the driver a recent version of ceph (unstable/testin git 
> head or 0.20.3 once it is released) is needed and you have to 
> "--enable-rbd" when running configure.
> 
> Additional information is available on the Ceph-Wiki:
> 
> http://ceph.newdream.net/wiki/Kvm-rbd
> 
> The patch is based on git://repo.or.cz/qemu/kevin.git block

Signed-off-by line is missing.

> ---
>  Makefile          |    3 +
>  Makefile.objs     |    1 +
>  block/rbd.c       |  584 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  block/rbd_types.h |   52 +++++
>  configure         |   27 +++
>  5 files changed, 667 insertions(+), 0 deletions(-)
>  create mode 100644 block/rbd.c
>  create mode 100644 block/rbd_types.h
> 
> diff --git a/Makefile b/Makefile
> index 7986bf6..8d09612 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -27,6 +27,9 @@ configure: ;
>  $(call set-vpath, $(SRC_PATH):$(SRC_PATH)/hw)
>  
>  LIBS+=-lz $(LIBS_TOOLS)
> +ifdef CONFIG_RBD
> +LIBS+=-lrados
> +endif

You already write the -lrados option to config-host.mak in configure, so
this looks unnecessary.

>  
>  ifdef BUILD_DOCS
>  DOCS=qemu-doc.html qemu-tech.html qemu.1 qemu-img.1 qemu-nbd.8
> diff --git a/Makefile.objs b/Makefile.objs
> index 1a942e5..08dc11f 100644
> --- a/Makefile.objs
> +++ b/Makefile.objs
> @@ -18,6 +18,7 @@ block-nested-y += parallels.o nbd.o blkdebug.o
>  block-nested-$(CONFIG_WIN32) += raw-win32.o
>  block-nested-$(CONFIG_POSIX) += raw-posix.o
>  block-nested-$(CONFIG_CURL) += curl.o
> +block-nested-$(CONFIG_RBD) += rbd.o
>  
>  block-obj-y +=  $(addprefix block/, $(block-nested-y))
>  
> diff --git a/block/rbd.c b/block/rbd.c
> new file mode 100644
> index 0000000..375ae9d
> --- /dev/null
> +++ b/block/rbd.c
> @@ -0,0 +1,584 @@
> +/*
> + * QEMU Block driver for RADOS (Ceph)
> + *
> + * Copyright (C) 2010 Christian Brunner <address@hidden>
> + *
> + * 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 <sys/types.h>
> +#include <stdbool.h>
> +
> +#include <qemu-common.h>
> +
> +#include "rbd_types.h"
> +#include "module.h"
> +#include "block_int.h"
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <rados/librados.h>
> +
> +#include <signal.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;
> +} RBDAIOCB;
> +
> +typedef struct RADOSCB {
> +    int rcbid;
> +    RBDAIOCB *acb;
> +    int done;
> +    int64_t segsize;
> +    char *buf;
> +} RADOSCB;
> +
> +typedef struct RBDRVRBDState {
> +    rados_pool_t pool;
> +    char name[RBD_MAX_OBJ_NAME_SIZE];
> +    int name_len;

name_len looks unused.

> +    uint64_t size;
> +    uint64_t objsize;
> +} RBDRVRBDState;

Hm, you mean BDRVRBDState?

Maybe ceph would have been a better driver name to avoid such type
names. ;-)

> +
> +typedef struct rbd_obj_header_ondisk RbdHeader1;
> +
> +static int rbd_parsename(const char *filename, char *pool, char *name)
> +{
> +    const char *rbdname;
> +    char *p, *n;
> +    int l;
> +
> +    if (!strstart(filename, "rbd:", &rbdname)) {
> +        return -EINVAL;
> +    }
> +
> +    pstrcpy(pool, 2 * RBD_MAX_SEG_NAME_SIZE, rbdname);

Why twice the size? The callers pass a char[RBD_MAX_SEG_NAME_SIZE], so
doesn't this allow buffer overflows?

> +    p = strchr(pool, '/');
> +    if (p == NULL) {
> +        return -EINVAL;
> +    }
> +
> +    *p = '\0';
> +    n = ++p;

Why introduce a new variable here? p isn't used any more afterwards.

> +
> +    l = strlen(n);
> +
> +    if (l > RBD_MAX_OBJ_NAME_SIZE) {
> +        fprintf(stderr, "object name to long\n");

Off by one, you need to consider the trailing '\0'.

Also, please use error_report instead of fprintf(stderr, ...) for real
error messages. Directly printing to stderr is okay for debug code.

> +        return -EINVAL;
> +    } else if (l <= 0) {
> +        fprintf(stderr, "object name to short\n");
> +        return -EINVAL;
> +    }
> +
> +    strcpy(name, n);
> +
> +    return l;
> +}
> +
> +static int create_tmap_op(uint8_t op, const char *name, char **tmap_desc)
> +{
> +    uint32_t len = strlen(name);
> +    uint32_t total_len = 1 + (sizeof(uint32_t) + len) + sizeof(uint32_t);    
>    /* encoding op + name + empty buffer */

This is more than 80 characters.

> +    char *desc;
> +
> +    desc = qemu_malloc(total_len);
> +    if (!desc) {
> +        return -ENOMEM;
> +    }

qemu_malloc never returns NULL.

> +
> +    *tmap_desc = desc;
> +
> +    *desc = op;
> +    desc++;
> +    memcpy(desc, &len, sizeof(len));
> +    desc += sizeof(len);
> +    memcpy(desc, name, len);
> +    desc += len;
> +    len = 0;
> +    memcpy(desc, &len, sizeof(len));
> +    desc += sizeof(len);
> +
> +    return 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 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_SEG_NAME_SIZE];
> +    RbdHeader1 header;
> +    rados_pool_t p;
> +    int name_len;
> +    int ret;
> +
> +    if ((name_len = rbd_parsename(filename, pool, name)) < 0) {

name_len is unused.

> +        return -EINVAL;
> +    }
> +
> +    snprintf(n, RBD_MAX_SEG_NAME_SIZE, "%s%s", name, RBD_SUFFIX);

n should probably be some bytes longer than name to contain RBD_SUFFIX
additionally. Otherwise, checking the return value might be a good idea.

> +
> +    /* 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 || ((objsize - 1) & objsize)) {    /* not a 
> power of 2? */

!objsize can't happen here, it's the if condition above.

> +                    fprintf(stderr, "obj size needs to be power of 2\n");
> +                    return -EINVAL;
> +                }
> +                if (objsize < 4096) {
> +                    fprintf(stderr, "obj size too small\n");
> +                    return -EINVAL;
> +                }
> +
> +                for (obj_order = 0; obj_order < 64; obj_order++) {
> +                    if (objsize == 1)
> +                        break;

Missing braces.

> +                    objsize >>= 1;
> +                }
> +            }
> +        }
> +        options++;
> +    }
> +
> +    memset(&header, 0, sizeof(header));
> +    pstrcpy(header.text, sizeof(header.text), rbd_text);
> +    pstrcpy(header.signature, sizeof(header.signature), rbd_signature);
> +    pstrcpy(header.version, sizeof(header.version), rbd_version);
> +    header.image_size = bytes;
> +    cpu_to_le64s((uint64_t *) & header.image_size);
> +    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;
> +    cpu_to_le32s(&header.snap_count);
> +
> +    if (rados_initialize(0, NULL) < 0) {
> +        fprintf(stderr, "error initializing\n");
> +        return -EIO;
> +    }
> +
> +    if (rados_open_pool(pool, &p)) {
> +        fprintf(stderr, "error opening pool %s\n", pool);
> +        return -EIO;

No need for rados_deinitialize() here?

> +    }
> +
> +    /* check for existing rbd header file */
> +    ret = rados_stat(p, n, &size, &mtime);
> +    if (ret == 0) {
> +        ret=-EEXIST;
> +        goto done;
> +    }
> +
> +    /* 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;
> +}
> +
> +static int rbd_open(BlockDriverState *bs, const char *filename, int flags)
> +{
> +    RBDRVRBDState *s = bs->opaque;
> +    char pool[RBD_MAX_SEG_NAME_SIZE];
> +    char n[RBD_MAX_SEG_NAME_SIZE];
> +    char hbuf[4096];
> +
> +    if ((s->name_len = rbd_parsename(filename, pool, s->name)) < 0) {
> +        return -EINVAL;
> +    }
> +    snprintf(n, RBD_MAX_SEG_NAME_SIZE, "%s%s", s->name, RBD_SUFFIX);
> +
> +    if (rados_initialize(0, NULL) < 0) {
> +        fprintf(stderr, "error initializing\n");
> +        return -EIO;
> +    }

What error codes do these rados_* functions return? Can we return
something more meaningful than -EIO? Same question for the following calls.

> +
> +    if (rados_open_pool(pool, &s->pool)) {
> +        fprintf(stderr, "error opening pool %s\n", pool);
> +        return -EIO;
> +    }

rados_deinitialize? (same for the following return statements)

> +
> +    if (rados_read(s->pool, n, 0, hbuf, 4096) < 0) {
> +        fprintf(stderr, "error reading header from %s\n", s->name);
> +        return -EIO;
> +    }
> +    if (!strncmp(hbuf + 64, rbd_signature, 4)) {
> +        if (!strncmp(hbuf + 68, rbd_version, 8)) {
> +            RbdHeader1 *header;
> +
> +            header = (RbdHeader1 *) hbuf;
> +            le64_to_cpus((uint64_t *) & header->image_size);
> +            s->size = header->image_size;
> +            s->objsize = 1 << header->options.order;
> +        } else {
> +            fprintf(stderr, "Unknown image version %s\n", hbuf + 68);
> +            return -EIO;
> +        }
> +    } else {
> +        fprintf(stderr, "Invalid header signature %s\n", hbuf + 64);
> +        return -EIO;
> +    }

Can't you go on like above, i.e. check the string and if the check fails
return an error? Would probably be more readable than this nesting.

Also, EIO for a failed string comparison is surely not the right error code?

> +
> +    return 0;
> +}
> +
> +static void rbd_close(BlockDriverState *bs)
> +{
> +    RBDRVRBDState *s = bs->opaque;
> +
> +    rados_close_pool(s->pool);
> +    rados_deinitialize();
> +}
> +
> +static int rbd_rw(BlockDriverState *bs, int64_t sector_num,
> +                  uint8_t *buf, int nb_sectors, int write)
> +{
> +    RBDRVRBDState *s = bs->opaque;
> +    char n[RBD_MAX_SEG_NAME_SIZE];
> +
> +    int64_t segnr, segoffs, segsize, r;
> +    int64_t off, size;
> +
> +    off = sector_num * 512;
> +    size = nb_sectors * 512;

Please use BDRV_SECTOR_SIZE.

> +    segnr = (int64_t) (off / s->objsize);
> +    segoffs = (int64_t) (off % s->objsize);
> +    segsize = (int64_t) (s->objsize - segoffs);

Why the type casts? Do they make any difference in this place?

> +
> +    while (size > 0) {
> +        if (size < segsize) {
> +            segsize = size;
> +        }
> +
> +        snprintf(n, RBD_MAX_SEG_NAME_SIZE, "%s.%012llx", s->name,
> +                 (long long unsigned int)segnr);

n is possibly to short, see above. Also you could use PRIx64 instead of
casting to long long.

> +
> +        if (write) {
> +            if ((r = rados_write(s->pool, n, segoffs, (const char *)buf,
> +                segsize)) < 0) {
> +                return r;
> +            }
> +        } else {
> +            r = rados_read(s->pool, n, segoffs, (char *)buf, segsize);
> +            if (r == -ENOENT) {
> +                memset(buf, 0, segsize);
> +            } else if (r < 0) {
> +                return(r);

These brackets look strange (and inconsistent with all other returns in
the code)

> +            } else if (r < segsize) {
> +                memset(buf + r, 0, segsize - r);
> +            }
> +            r = segsize;

What is this good for? r isn't used before it's overwritten in the next
loop iteration.

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

Again brackets.

> +}
> +
> +static int rbd_read(BlockDriverState *bs, int64_t sector_num,
> +                    uint8_t *buf, int nb_sectors)
> +{
> +    return rbd_rw(bs, sector_num, buf, nb_sectors, 0);
> +}
> +
> +static int rbd_write(BlockDriverState *bs, int64_t sector_num,
> +                     const uint8_t *buf, int nb_sectors)
> +{
> +    return rbd_rw(bs, sector_num, (uint8_t *) buf, nb_sectors, 1);
> +}
> +
> +static void rbd_aio_cancel(BlockDriverAIOCB *blockacb)
> +{
> +    RBDAIOCB *acb = (RBDAIOCB *) blockacb;
> +    qemu_bh_delete(acb->bh);
> +    acb->bh = NULL;
> +    qemu_aio_release(acb);
> +}
> +
> +static AIOPool rbd_aio_pool = {
> +    .aiocb_size = sizeof(RBDAIOCB),
> +    .cancel = rbd_aio_cancel,
> +};
> +
> +/* This is the callback function for rados_aio_read and _write */
> +static void rbd_finish_aiocb(rados_completion_t c, RADOSCB *rcb)
> +{
> +    RBDAIOCB *acb = rcb->acb;
> +    int64_t r;
> +    int i;
> +
> +    acb->aiocnt--;
> +    r = rados_aio_get_return_value(c);
> +    rados_aio_release(c);
> +    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) {
> +            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;
> +        }
> +    }
> +    qemu_free(rcb);
> +    i = 0;
> +    if (!acb->aiocnt && acb->bh) {
> +        qemu_bh_schedule(acb->bh);
> +    }
> +}
> +
> +/* 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)

For this function the same applies as for the synchronous one.

> +{
> +    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;
> +
> +    RBDRVRBDState *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;
> +
> +    if (!acb->bh) {
> +        acb->bh = qemu_bh_new(rbd_aio_bh_cb, acb);
> +    }
> +
> +    if (write) {
> +        qemu_iovec_to_buffer(acb->qiov, acb->bounce);
> +    }
> +
> +    buf = acb->bounce;
> +
> +    off = sector_num * 512;
> +    size = nb_sectors * 512;
> +    segnr = (int64_t) (off / s->objsize);
> +    segoffs = (int64_t) (off % s->objsize);
> +    segsize = (int64_t) (s->objsize - segoffs);
> +
> +    last_segnr = ((off + size - 1) / s->objsize);
> +    acb->aiocnt = (last_segnr - segnr) + 1;
> +
> +    while (size > 0) {
> +        if (size < segsize) {
> +            segsize = size;
> +        }
> +
> +        snprintf(n, RBD_MAX_SEG_NAME_SIZE, "%s.%012llx", s->name,
> +                 (long long unsigned int)segnr);
> +
> +        rcb = qemu_malloc(sizeof(RADOSCB));
> +        rcb->done = 0;
> +        rcb->acb = acb;
> +        rcb->segsize = segsize;
> +        rcb->buf = buf;
> +
> +        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)
> +{
> +    RBDRVRBDState *s = bs->opaque;
> +    bdi->cluster_size = s->objsize;
> +    return 0;
> +}
> +
> +static int64_t rbd_getlength(BlockDriverState * bs)
> +{
> +    RBDRVRBDState *s = bs->opaque;
> +
> +    return s->size;
> +}
> +
> +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(RBDRVRBDState),
> +    .bdrv_file_open = rbd_open,
> +    .bdrv_read = rbd_read,
> +    .bdrv_write = rbd_write,
> +    .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,
> +};

Could you align the = to be on the same column?

> +
> +static void bdrv_rbd_init(void)
> +{
> +    bdrv_register(&bdrv_rbd);
> +}
> +
> +block_init(bdrv_rbd_init);
> diff --git a/block/rbd_types.h b/block/rbd_types.h
> new file mode 100644
> index 0000000..3a16a26
> --- /dev/null
> +++ b/block/rbd_types.h
> @@ -0,0 +1,52 @@

We need a header comment with copyright/license.

> +#ifndef QEMU_BLOCK_RBD_TYPES_H
> +#define QEMU_BLOCK_RBD_TYPES_H
> +
> +
> +/*
> + * rbd image 'foo' consists of objects
> + *   foo.rbd      - image metadata
> + *   foo.00000000 

Trailing whitespace.

> + *   foo.00000001
> + *   ...          - data
> + */
> +
> +#define RBD_SUFFIX              ".rbd"
> +#define RBD_DIRECTORY           "rbd_directory"
> +
> +#define RBD_DEFAULT_OBJ_ORDER   22   /* 4MB */
> +
> +#define RBD_MAX_OBJ_NAME_SIZE   96
> +#define RBD_MAX_SEG_NAME_SIZE   128
> +
> +#define RBD_COMP_NONE           0
> +#define RBD_CRYPT_NONE          0
> +
> +static const char rbd_text[] = "<<< Rados Block Device Image >>>\n";
> +static const char rbd_signature[] = "RBD";
> +static const char rbd_version[] = "001.004";

Move these to rbd.c?

> +
> +struct rbd_obj_snap_ondisk {
> +    uint64_t id;
> +    uint64_t image_size;
> +} __attribute__((packed));
> +
> +struct rbd_obj_header_ondisk {
> +    char text[64];
> +    char signature[4];
> +    char version[8];
> +    struct {
> +        uint8_t order;
> +        uint8_t crypt_type;
> +        uint8_t comp_type;
> +        uint8_t unused;
> +    } __attribute__((packed)) options;
> +    uint64_t image_size;
> +    uint64_t snap_seq;
> +    uint32_t snap_count;
> +    uint32_t reserved;
> +    uint64_t snap_names_len;
> +    struct rbd_obj_snap_ondisk snaps[0];
> +} __attribute__((packed));
> +
> +
> +#endif
> diff --git a/configure b/configure
> index 3cd2c5f..7d70bf8 100755
> --- a/configure
> +++ b/configure
> @@ -299,6 +299,7 @@ pkgversion=""
>  check_utests="no"
>  user_pie="no"
>  zero_malloc=""
> +rbd="no"

Shouldn't it default to auto-detection? (rbd="")

>  
>  # OS specific
>  if check_define __linux__ ; then
> @@ -660,6 +661,8 @@ for opt do
>    ;;
>    --enable-vhost-net) vhost_net="yes"
>    ;;
> +  --enable-rbd) rbd="yes"
> +  ;;

Would need a --disable-rbd flag then, too.

>    *) echo "ERROR: unknown option $opt"; show_help="yes"
>    ;;
>    esac
> @@ -826,6 +829,7 @@ echo "  --enable-docs            enable documentation 
> build"
>  echo "  --disable-docs           disable documentation build"
>  echo "  --disable-vhost-net      disable vhost-net acceleration support"
>  echo "  --enable-vhost-net       enable vhost-net acceleration support"
> +echo "  --enable-rbd          enable building the rados block device (rbd)"
>  echo ""
>  echo "NOTE: The object files are built at the place where configure is 
> launched"
>  exit 1
> @@ -1579,6 +1583,25 @@ if test "$mingw32" != yes -a "$pthread" = no; then
>  fi
>  
>  ##########################################
> +# rbd probe
> +if test "$rbd" != "no" ; then
> +  cat > $TMPC <<EOF
> +#include <stdio.h>
> +#include <rados/librados.h>
> +int main(void) { rados_initialize(0, NULL); return 0; }
> +EOF
> +  if compile_prog "" "-lrados -lcrypto" ; then
> +    rbd=yes
> +    LIBS="$LIBS -lrados -lcrypto"

Other block features like curl or Linux AIO use $lib_tools and
$lib_softmmu here.

> +  else
> +    if test "$rbd" = "yes" ; then
> +      feature_not_found "rados block device"
> +    fi
> +    rbd=no
> +  fi
> +fi

But if you didn't want to auto-detect, this is more complicated than it
needs to be.

Kevin