Please see patches for rationale.
Libvirt patches using this new flag will be posted soon-ish (after
cleanup).
Peter Krempa (2):
block: commit: Allow users to request only format driver names in
backing file format
block: stream: Allow users to request only format driver names in
backing file format
block.c | 37 +++++++++++++++++++++-----
block/commit.c | 6 ++++-
block/monitor/block-hmp-cmds.c | 2 +-
block/stream.c | 10 ++++++-
blockdev.c | 13 +++++++++
include/block/block-global-state.h | 3 ++-
include/block/block_int-common.h | 4 ++-
include/block/block_int-global-state.h | 6 +++++
qapi/block-core.json | 22 +++++++++++++--
tests/unit/test-bdrv-drain.c | 3 ++-
10 files changed, 91 insertions(+), 15 deletions(-)