Since Ceph version Infernalis (9.2.0) the new fast-diff mechanism
of RBD allows for querying actual rbd image usage.

Prior to this version there was no easy and fast way to query how
much allocation a RBD image had inside a Ceph cluster.

To use the fast-diff feature it needs to be enabled per RBD image
and is only supported by Ceph cluster running version Infernalis
(9.2.0) or newer.

The fast-diff feature disabled or fast-diff map is marked as invalid,
qemu-img will report an allocation identical to the image capacity.

'qemu-img info rbd:cepharm/liyi-rbd' might output for example:

  image: json:{"driver": "raw", "file": {"pool": "cepharm",
  "image": "liyi-rbd", "driver": "rbd"}}
  file format: raw
  virtual size: 20 GiB (21474836480 bytes)
  disk size: 0 B
  cluster_size: 4194304

Newly created rbds will have the fast-diff feature enabled.

Signed-off-by: Yi Li <yili@winhong.com>
---
 block/rbd.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 103 insertions(+)

diff --git a/block/rbd.c b/block/rbd.c
index 617553b022..c1e68ff7e9 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -1107,6 +1107,108 @@ static int64_t qemu_rbd_getlength(BlockDriverState *bs)
     return info.size;
 }
 
+#if LIBRBD_VERSION_CODE > 265
+static int disk_usage_callback(uint64_t offset, size_t len, int exists,
+                               void *arg)
+{
+  uint64_t *used_size = (uint64_t *)(arg);
+  if (exists) {
+    (*used_size) += len;
+  }
+  return 0;
+}
+
+static int qemu_rbd_getflags(rbd_image_t image, uint64_t *flags)
+{
+    int r;
+
+    r = rbd_get_flags(image, flags);
+    if (r < 0) {
+        return r;
+    }
+    return 0;
+}
+
+static bool qemu_rbd_use_fastdiff(uint64_t features, uint64_t flags)
+{
+    return (((features & RBD_FEATURE_FAST_DIFF) != 0ULL) &&
+            ((flags & RBD_FLAG_FAST_DIFF_INVALID) == 0ULL));
+}
+
+static int qemu_rbd_set_allocation(rbd_image_t image,
+                                   rbd_image_info_t *info,
+                                   uint64_t *used_size)
+{
+    int r;
+    /*
+     * RBD image fast-diff feature enabled
+     * Querying for actual allocation.
+     */
+    r = rbd_diff_iterate2(image, NULL, 0, info->size, 0, 1,
+                          &disk_usage_callback,
+                          used_size);
+    if (r < 0) {
+        return r;
+    }
+    return 0;
+}
+
+#else
+static int qemu_rbd_getflags(rbd_image_t image G_GNUC_UNUSED, uint64_t *flags)
+{
+    *flags = 0;
+    return 0;
+}
+
+static bool qemu_rbd_use_fastdiff(uint64_t features G_GNUC_UNUSED,
+                                  uint64_t feature_flags G_GNUC_UNUSED)
+{
+    return false;
+}
+
+static int qemu_rbd_set_allocation(rbd_image_t image G_GNUC_UNUSED,
+                                   rbd_image_info_t *info _GNUC_UNUSED,
+                                   uint64_t *used_size _GNUC_UNUSED)
+{
+    return 0;
+}
+#endif
+
+static int64_t qemu_rbd_allocated_file_size(BlockDriverState *bs)
+{
+    BDRVRBDState *s = bs->opaque;
+    rbd_image_info_t info;
+    int r;
+    uint64_t used_size = 0;
+    uint64_t features = 0;
+    uint64_t flags = 0;
+
+    r = rbd_stat(s->image, &info, sizeof(info));
+    if (r < 0) {
+        return r;
+    }
+
+    r = rbd_get_features(s->image, &features);
+    if (r < 0) {
+        return r;
+    }
+
+    r = qemu_rbd_getflags(s->image, &flags);
+    if (r < 0) {
+        return r;
+    }
+
+    if (qemu_rbd_use_fastdiff(features, flags)) {
+        r = qemu_rbd_set_allocation(s->image, &info, &used_size);
+        if (r < 0) {
+            return r;
+        }
+    } else {
+        used_size = info.size;
+    }
+    return used_size;
+}
+
 static int coroutine_fn qemu_rbd_co_truncate(BlockDriverState *bs,
                                              int64_t offset,
                                              bool exact,
@@ -1316,6 +1418,7 @@ static BlockDriver bdrv_rbd = {
     .bdrv_get_info          = qemu_rbd_getinfo,
     .create_opts            = &qemu_rbd_create_opts,
     .bdrv_getlength         = qemu_rbd_getlength,
+    .bdrv_get_allocated_file_size = qemu_rbd_allocated_file_size,
     .bdrv_co_truncate       = qemu_rbd_co_truncate,
     .protocol_name          = "rbd",
 
-- 
2.25.3

ping ?

On 6/11/20, Yi Li <yili@winhong.com> wrote:
> Since Ceph version Infernalis (9.2.0) the new fast-diff mechanism
> of RBD allows for querying actual rbd image usage.
>
> Prior to this version there was no easy and fast way to query how
> much allocation a RBD image had inside a Ceph cluster.
>
> To use the fast-diff feature it needs to be enabled per RBD image
> and is only supported by Ceph cluster running version Infernalis
> (9.2.0) or newer.
>
> The fast-diff feature disabled or fast-diff map is marked as invalid,
> qemu-img will report an allocation identical to the image capacity.
>
> 'qemu-img info rbd:cepharm/liyi-rbd' might output for example:
>
>   image: json:{"driver": "raw", "file": {"pool": "cepharm",
>   "image": "liyi-rbd", "driver": "rbd"}}
>   file format: raw
>   virtual size: 20 GiB (21474836480 bytes)
>   disk size: 0 B
>   cluster_size: 4194304
>
> Newly created rbds will have the fast-diff feature enabled.
>
> Signed-off-by: Yi Li <yili@winhong.com>
> ---
>  block/rbd.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 103 insertions(+)
>
> diff --git a/block/rbd.c b/block/rbd.c
> index 617553b022..c1e68ff7e9 100644
> --- a/block/rbd.c
> +++ b/block/rbd.c
> @@ -1107,6 +1107,108 @@ static int64_t qemu_rbd_getlength(BlockDriverState
> *bs)
>      return info.size;
>  }
>
> +#if LIBRBD_VERSION_CODE > 265
> +static int disk_usage_callback(uint64_t offset, size_t len, int exists,
> +                               void *arg)
> +{
> +  uint64_t *used_size = (uint64_t *)(arg);
> +  if (exists) {
> +    (*used_size) += len;
> +  }
> +  return 0;
> +}
> +
> +static int qemu_rbd_getflags(rbd_image_t image, uint64_t *flags)
> +{
> +    int r;
> +
> +    r = rbd_get_flags(image, flags);
> +    if (r < 0) {
> +        return r;
> +    }
> +    return 0;
> +}
> +
> +static bool qemu_rbd_use_fastdiff(uint64_t features, uint64_t flags)
> +{
> +    return (((features & RBD_FEATURE_FAST_DIFF) != 0ULL) &&
> +            ((flags & RBD_FLAG_FAST_DIFF_INVALID) == 0ULL));
> +}
> +
> +static int qemu_rbd_set_allocation(rbd_image_t image,
> +                                   rbd_image_info_t *info,
> +                                   uint64_t *used_size)
> +{
> +    int r;
> +    /*
> +     * RBD image fast-diff feature enabled
> +     * Querying for actual allocation.
> +     */
> +    r = rbd_diff_iterate2(image, NULL, 0, info->size, 0, 1,
> +                          &disk_usage_callback,
> +                          used_size);
> +    if (r < 0) {
> +        return r;
> +    }
> +    return 0;
> +}
> +
> +#else
> +static int qemu_rbd_getflags(rbd_image_t image G_GNUC_UNUSED, uint64_t
> *flags)
> +{
> +    *flags = 0;
> +    return 0;
> +}
> +
> +static bool qemu_rbd_use_fastdiff(uint64_t features G_GNUC_UNUSED,
> +                                  uint64_t feature_flags G_GNUC_UNUSED)
> +{
> +    return false;
> +}
> +
> +static int qemu_rbd_set_allocation(rbd_image_t image G_GNUC_UNUSED,
> +                                   rbd_image_info_t *info _GNUC_UNUSED,
> +                                   uint64_t *used_size _GNUC_UNUSED)
> +{
> +    return 0;
> +}
> +#endif
> +
> +static int64_t qemu_rbd_allocated_file_size(BlockDriverState *bs)
> +{
> +    BDRVRBDState *s = bs->opaque;
> +    rbd_image_info_t info;
> +    int r;
> +    uint64_t used_size = 0;
> +    uint64_t features = 0;
> +    uint64_t flags = 0;
> +
> +    r = rbd_stat(s->image, &info, sizeof(info));
> +    if (r < 0) {
> +        return r;
> +    }
> +
> +    r = rbd_get_features(s->image, &features);
> +    if (r < 0) {
> +        return r;
> +    }
> +
> +    r = qemu_rbd_getflags(s->image, &flags);
> +    if (r < 0) {
> +        return r;
> +    }
> +
> +    if (qemu_rbd_use_fastdiff(features, flags)) {
> +        r = qemu_rbd_set_allocation(s->image, &info, &used_size);
> +        if (r < 0) {
> +            return r;
> +        }
> +    } else {
> +        used_size = info.size;
> +    }
> +    return used_size;
> +}
> +
>  static int coroutine_fn qemu_rbd_co_truncate(BlockDriverState *bs,
>                                               int64_t offset,
>                                               bool exact,
> @@ -1316,6 +1418,7 @@ static BlockDriver bdrv_rbd = {
>      .bdrv_get_info          = qemu_rbd_getinfo,
>      .create_opts            = &qemu_rbd_create_opts,
>      .bdrv_getlength         = qemu_rbd_getlength,
> +    .bdrv_get_allocated_file_size = qemu_rbd_allocated_file_size,
>      .bdrv_co_truncate       = qemu_rbd_co_truncate,
>      .protocol_name          = "rbd",
>
> --
> 2.25.3
>
>
>
>