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>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2021-08-24 11:38:28 +03:00 committed by Hanna Reitz
parent d003e0aece
commit 49577723d4
5 changed files with 26 additions and 28 deletions

View file

@ -407,7 +407,6 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
int64_t len, target_len;
BackupBlockJob *job = NULL;
int64_t cluster_size;
BdrvRequestFlags write_flags;
BlockDriverState *cbw = NULL;
BlockCopyState *bcs = NULL;
@ -504,26 +503,8 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
goto error;
}
/*
* 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
*/
write_flags = (bdrv_chain_contains(target, bs) ? BDRV_REQ_SERIALISING : 0) |
(compress ? BDRV_REQ_WRITE_COMPRESSED : 0),
cbw = bdrv_cbw_append(bs, target, filter_node_name,
cluster_size, perf,
write_flags, &bcs, errp);
cluster_size, perf, compress, &bcs, errp);
if (!cbw) {
goto error;
}