--- /dev/null
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Fiona Ebner <f.ebner@proxmox.com>
+Date: Thu, 11 Apr 2024 11:29:26 +0200
+Subject: [PATCH] copy-before-write: allow specifying minimum cluster size
+
+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.
+
+Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
+Signed-off-by: Thomas Lamprecht <t.lamprecht@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);
+ } 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);
+ }
+
+- return MAX(BLOCK_COPY_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
++ return MAX(min_cluster_size,
++ MAX(BLOCK_COPY_CLUSTER_SIZE_DEFAULT, bdi.cluster_size));
+ }
+
+ 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)) {
++ 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);
+ if (cluster_size < 0) {
+ return NULL;
+ }
+diff --git a/block/copy-before-write.c b/block/copy-before-write.c
+index cd65524e26..ac05a4993f 100644
+--- a/block/copy-before-write.c
++++ b/block/copy-before-write.c
+@@ -477,7 +477,8 @@ 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);
+ 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 d796d49abb..edbf6e78b9 100644
+--- a/qapi/block-core.json
++++ b/qapi/block-core.json
+@@ -4930,12 +4930,18 @@
+ # @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 8.1)
++#
+ # 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' } }
+
+ ##
+ # @BlockdevOptions:
projects / pve-qemu.git / blobdiff