diff options
| author | Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> | 2021-08-24 11:38:28 +0300 |
|---|---|---|
| committer | Hanna Reitz <hreitz@redhat.com> | 2021-09-01 12:57:31 +0200 |
| commit | 49577723d40f56f7ac3d2f880423ae6652a2922d (patch) | |
| tree | 24edb6cca1e166358bf78be39ffe1cee0f2e8c37 /block/block-copy.c | |
| parent | d003e0aeced533074341c88fe6b58f97f8136397 (diff) | |
block-copy: move detecting fleecing scheme to block-copy
We want to simplify initialization interface of copy-before-write
filter as we are going to make it public. So, let's detect fleecing
scheme exactly in block-copy code, to not pass this information through
extra levels.
Why not just set BDRV_REQ_SERIALISING unconditionally: because we are
going to implement new more efficient fleecing scheme which will not
rely on backing feature.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20210824083856.17408-7-vsementsov@virtuozzo.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Diffstat (limited to 'block/block-copy.c')
| -rw-r--r-- | block/block-copy.c | 24 |
1 files changed, 21 insertions, 3 deletions
diff --git a/block/block-copy.c b/block/block-copy.c index 0becad52da..58b4345a5a 100644 --- a/block/block-copy.c +++ b/block/block-copy.c @@ -317,10 +317,11 @@ static uint32_t block_copy_max_transfer(BdrvChild *source, BdrvChild *target) BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target, int64_t cluster_size, bool use_copy_range, - BdrvRequestFlags write_flags, Error **errp) + bool compress, Error **errp) { BlockCopyState *s; BdrvDirtyBitmap *copy_bitmap; + bool is_fleecing; copy_bitmap = bdrv_create_dirty_bitmap(source->bs, cluster_size, NULL, errp); @@ -329,6 +330,22 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target, } bdrv_disable_dirty_bitmap(copy_bitmap); + /* + * If source is in backing chain of target assume that target is going to be + * used for "image fleecing", i.e. it should represent a kind of snapshot of + * source at backup-start point in time. And target is going to be read by + * somebody (for example, used as NBD export) during backup job. + * + * In this case, we need to add BDRV_REQ_SERIALISING write flag to avoid + * intersection of backup writes and third party reads from target, + * otherwise reading from target we may occasionally read already updated by + * guest data. + * + * For more information see commit f8d59dfb40bb and test + * tests/qemu-iotests/222 + */ + is_fleecing = bdrv_chain_contains(target->bs, source->bs); + s = g_new(BlockCopyState, 1); *s = (BlockCopyState) { .source = source, @@ -336,7 +353,8 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target, .copy_bitmap = copy_bitmap, .cluster_size = cluster_size, .len = bdrv_dirty_bitmap_size(copy_bitmap), - .write_flags = write_flags, + .write_flags = (is_fleecing ? BDRV_REQ_SERIALISING : 0) | + (compress ? BDRV_REQ_WRITE_COMPRESSED : 0), .mem = shres_create(BLOCK_COPY_MAX_MEM), .max_transfer = QEMU_ALIGN_DOWN( block_copy_max_transfer(source, target), @@ -351,7 +369,7 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target, * behalf). */ s->method = COPY_READ_WRITE_CLUSTER; - } else if (write_flags & BDRV_REQ_WRITE_COMPRESSED) { + } else if (compress) { /* Compression supports only cluster-size writes and no copy-range. */ s->method = COPY_READ_WRITE_CLUSTER; } else { |