Fiona Ebner <f.eb...@proxmox.com> writes:
> Useful to make discard-source work in the context of backup fleecing
> when the fleecing image has a larger granularity than the backup
> target.
>
> Copy-before-write operations will use at least this granularity and in
> particular, discard requests to the source node will too. If the
> granularity is too small, they will just be aligned down in
> cbw_co_pdiscard_snapshot() and thus effectively ignored.
>
> The QAPI uses uint32 so the value will be non-negative, but still fit
> into a uint64_t.
>
> Suggested-by: Vladimir Sementsov-Ogievskiy <vsement...@yandex-team.ru>
> Signed-off-by: Fiona Ebner <f.eb...@proxmox.com>
> ---
> block/block-copy.c | 17 +++++++++++++----
> block/copy-before-write.c | 3 ++-
> include/block/block-copy.h | 1 +
> qapi/block-core.json | 8 +++++++-
> 4 files changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/block/block-copy.c b/block/block-copy.c
> index 7e3b378528..adb1cbb440 100644
> --- a/block/block-copy.c
> +++ b/block/block-copy.c
> @@ -310,6 +310,7 @@ void block_copy_set_copy_opts(BlockCopyState *s, bool
> use_copy_range,
> }
>
> static int64_t block_copy_calculate_cluster_size(BlockDriverState *target,
> + int64_t min_cluster_size,
> Error **errp)
> {
> int ret;
> @@ -335,7 +336,7 @@ static int64_t
> block_copy_calculate_cluster_size(BlockDriverState *target,
> "used. If the actual block size of the target exceeds "
> "this default, the backup may be unusable",
> BLOCK_COPY_CLUSTER_SIZE_DEFAULT);
> - return BLOCK_COPY_CLUSTER_SIZE_DEFAULT;
> + return MAX(min_cluster_size, BLOCK_COPY_CLUSTER_SIZE_DEFAULT);
min_cluster_size is int64_t, BLOCK_COPY_CLUSTER_SIZE_DEFAULT is int, and
gets converted to int64_t. The return type is int64_t. Okay.
> } else if (ret < 0 && !target_does_cow) {
> error_setg_errno(errp, -ret,
> "Couldn't determine the cluster size of the target image, "
> @@ -345,16 +346,18 @@ static int64_t
> block_copy_calculate_cluster_size(BlockDriverState *target,
> return ret;
> } else if (ret < 0 && target_does_cow) {
> /* Not fatal; just trudge on ahead. */
> - return BLOCK_COPY_CLUSTER_SIZE_DEFAULT;
> + return MAX(min_cluster_size, BLOCK_COPY_CLUSTER_SIZE_DEFAULT);
Same.
> }
>
> - return MAX(BLOCK_COPY_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
> + return MAX(min_cluster_size,
> + MAX(BLOCK_COPY_CLUSTER_SIZE_DEFAULT, bdi.cluster_size));
Similar: bdi.cluster_size is int.
> }
>
> BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
> BlockDriverState *copy_bitmap_bs,
> const BdrvDirtyBitmap *bitmap,
> bool discard_source,
> + int64_t min_cluster_size,
> Error **errp)
> {
> ERRP_GUARD();
> @@ -365,7 +368,13 @@ BlockCopyState *block_copy_state_new(BdrvChild *source,
> BdrvChild *target,
>
> GLOBAL_STATE_CODE();
>
> - cluster_size = block_copy_calculate_cluster_size(target->bs, errp);
> + if (min_cluster_size && !is_power_of_2(min_cluster_size)) {
min_cluster_size is int64_t, is_power_of_2() takes uint64_t. Bad if
min_cluster_size is negative. Could this happen?
> + error_setg(errp, "min-cluster-size needs to be a power of 2");
> + return NULL;
> + }
> +
> + cluster_size = block_copy_calculate_cluster_size(target->bs,
> + min_cluster_size, errp);
min_cluster_size is int64_t, block_copy_calculate_cluster_size() takes
int64_t, returns int64_t, and cluster_size is int64_t. Good.
> if (cluster_size < 0) {
> return NULL;
> }
> diff --git a/block/copy-before-write.c b/block/copy-before-write.c
> index dac57481c5..f9896c6c1e 100644
> --- a/block/copy-before-write.c
> +++ b/block/copy-before-write.c
> @@ -476,7 +476,8 @@ static int cbw_open(BlockDriverState *bs, QDict *options,
> int flags,
>
> s->discard_source = flags & BDRV_O_CBW_DISCARD_SOURCE;
> s->bcs = block_copy_state_new(bs->file, s->target, bs, bitmap,
> - flags & BDRV_O_CBW_DISCARD_SOURCE, errp);
> + flags & BDRV_O_CBW_DISCARD_SOURCE,
> + opts->min_cluster_size, errp);
@opts is BlockdevOptionsCbw *, opts->min_cluster_size is uint32_t (see
last hunk), block_copy_state_new() takes int64_t: opts->min_cluster_size
gets zero-extended. Okay.
> if (!s->bcs) {
> error_prepend(errp, "Cannot create block-copy-state: ");
> return -EINVAL;
> diff --git a/include/block/block-copy.h b/include/block/block-copy.h
> index bdc703bacd..77857c6c68 100644
> --- a/include/block/block-copy.h
> +++ b/include/block/block-copy.h
> @@ -28,6 +28,7 @@ BlockCopyState *block_copy_state_new(BdrvChild *source,
> BdrvChild *target,
> BlockDriverState *copy_bitmap_bs,
> const BdrvDirtyBitmap *bitmap,
> bool discard_source,
> + int64_t min_cluster_size,
> Error **errp);
>
> /* Function should be called prior any actual copy request */
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 0a72c590a8..85c8f88f6e 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -4625,12 +4625,18 @@
> # @on-cbw-error parameter will decide how this failure is handled.
> # Default 0. (Since 7.1)
> #
> +# @min-cluster-size: Minimum size of blocks used by copy-before-write
> +# operations. Has to be a power of 2. No effect if smaller than
> +# the maximum of the target's cluster size and 64 KiB. Default 0.
> +# (Since 9.0)
> +#
> # Since: 6.2
> ##
> { 'struct': 'BlockdevOptionsCbw',
> 'base': 'BlockdevOptionsGenericFormat',
> 'data': { 'target': 'BlockdevRef', '*bitmap': 'BlockDirtyBitmap',
> - '*on-cbw-error': 'OnCbwError', '*cbw-timeout': 'uint32' } }
> + '*on-cbw-error': 'OnCbwError', '*cbw-timeout': 'uint32',
> + '*min-cluster-size': 'uint32' } }
Elsewhere in the schema, we use either 'int' or 'size' for cluster-size.
Why the difference?
>
> ##
> # @BlockdevOptions:
