block: Split BLOCK_OP_TYPE_COMMIT to BLOCK_OP_TYPE_COMMIT_{SOURCE, TARGET}
Like BLOCK_OP_TYPE_BACKUP_SOURCE and BLOCK_OP_TYPE_BACKUP_TARGET, block-commit involves two asymmetric devices. This change is not user-visible (yet), because commit only works with device names. But once we enable backing reference in blockdev-add, or specifying node-name in block-commit command, we don't want the user to start two commit jobs on the same backing chain, which will corrupt things because of the final bdrv_swap. Before we have per category blockers, splitting this type is still better. [Resolved virtio-blk dataplane conflict by replacing BLOCK_OP_TYPE_COMMIT with both BLOCK_OP_TYPE_COMMIT_{SOURCE, TARGET}. They are safe since the block job runs in the same AioContext as the dataplane IOThread. --Stefan] Signed-off-by: NFam Zheng <famz@redhat.com> Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
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