[pve-devel] [HACK qemu 07/13] block/block-copy: always consider source cluster size too

[Fiona Ebner]

With backup fleecing, it might be necessary to discard the source.
There will be an assertion failure if bitmaps on the source side have
a bigger granularity than the block copy's cluster size, so just
consider the source side too.

This also supersedes the hunk in block/backup.c added by
"PVE-Backup: add backup-dump block driver".

Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>
---

Still need to wait on a response from upstream. For now this hack, so
that the RFC as a whole doesn't have to wait.

 block/backup.c     |  8 --------
 block/block-copy.c | 22 ++++++++++++++--------
 2 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/block/backup.c b/block/backup.c
index 51f9d28115..7950bff27e 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -435,14 +435,6 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
     }
 
     cluster_size = block_copy_cluster_size(bcs);
-    if (cluster_size < 0) {
-        goto error;
-    }
-
-    BlockDriverInfo bdi;
-    if (bdrv_get_info(bs, &bdi) == 0) {
-        cluster_size = MAX(cluster_size, bdi.cluster_size);
-    }
 
     if (perf->max_chunk && perf->max_chunk < cluster_size) {
         error_setg(errp, "Required max-chunk (%" PRIi64 ") is less than backup "
diff --git a/block/block-copy.c b/block/block-copy.c
index 05cfccfda8..cf750ef670 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -310,13 +310,19 @@ void block_copy_set_copy_opts(BlockCopyState *s, bool use_copy_range,
     }
 }
 
-static int64_t block_copy_calculate_cluster_size(BlockDriverState *target,
+static int64_t block_copy_calculate_cluster_size(BlockDriverState *source,
+                                                 BlockDriverState *target,
                                                  Error **errp)
 {
     int ret;
+    int64_t source_cluster_size = BLOCK_COPY_CLUSTER_SIZE_DEFAULT;
     BlockDriverInfo bdi;
     bool target_does_cow = bdrv_backing_chain_next(target);
 
+    if (bdrv_get_info(source, &bdi) == 0) {
+        source_cluster_size = MAX(source_cluster_size, bdi.cluster_size);
+    }
+
     /*
      * If there is no backing file on the target, we cannot rely on COW if our
      * backup cluster size is smaller than the target cluster size. Even for
@@ -327,11 +333,11 @@ static int64_t block_copy_calculate_cluster_size(BlockDriverState *target,
         /* Cluster size is not defined */
         warn_report("The target block device doesn't provide "
                     "information about the block size and it doesn't have a "
-                    "backing file. The default block size of %u bytes is "
+                    "backing file. The source's or default block size of %ld bytes is "
                     "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;
+                    "this value, the backup may be unusable",
+                    source_cluster_size);
+        return source_cluster_size;
     } else if (ret < 0 && !target_does_cow) {
         error_setg_errno(errp, -ret,
             "Couldn't determine the cluster size of the target image, "
@@ -341,10 +347,10 @@ 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 source_cluster_size;
     }
 
-    return MAX(BLOCK_COPY_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
+    return MAX(source_cluster_size, bdi.cluster_size);
 }
 
 BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
@@ -358,7 +364,7 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
     BdrvDirtyBitmap *copy_bitmap;
     bool is_fleecing;
 
-    cluster_size = block_copy_calculate_cluster_size(target->bs, errp);
+    cluster_size = block_copy_calculate_cluster_size(source->bs, target->bs, errp);
     if (cluster_size < 0) {
         return NULL;
     }
-- 
2.39.2