Enough innocent images have died because users called 'qemu-img snapshot' while the VM was still running. Educating the users doesn't seem to be a working strategy, so this series adds locking to qcow2 that refuses to access the image read-write from two processes.
Eric, this will require a libvirt update to deal with qemu crashes which leave locked images behind. The simplest thinkable way would be to unconditionally override the lock in libvirt whenever the option is present. In that case, libvirt VMs would be protected against concurrent non-libvirt accesses, but not the other way round. If you want more than that, libvirt would have to check somehow if it was its own VM that used the image and left the lock behind. I imagine that can't be too hard either. Also note that this kind of depends on Max's bdrv_close_all() series, but only in order to pass test case 142. This is not a bug in this series, but a preexisting one (bs->file can be closed before bs), and it becomes apparent when qemu fails to unlock an image due to this bug. Max's series fixes this. Kevin Wolf (10): qcow2: Write feature table only for v3 images qcow2: Write full header on image creation block: Assert no write requests under BDRV_O_INCOMING block: Fix error path in bdrv_invalidate_cache() block: Inactivate BDS when migration completes qemu-img: Prepare for locked images qcow2: Implement .bdrv_inactivate qcow2: Fix BDRV_O_INCOMING handling in qcow2_invalidate_cache() qcow2: Make image inaccessible after failed qcow2_invalidate_cache() qcow2: Add image locking block.c | 36 +++++++++ block/io.c | 2 + block/qcow2.c | 190 +++++++++++++++++++++++++++++++++++---------- block/qcow2.h | 7 +- docs/specs/qcow2.txt | 7 +- include/block/block.h | 2 + include/block/block_int.h | 1 + include/qapi/error.h | 1 + migration/migration.c | 7 ++ qapi/common.json | 3 +- qemu-img-cmds.hx | 10 ++- qemu-img.c | 96 +++++++++++++++++++---- qemu-img.texi | 20 ++++- qmp.c | 12 +++ tests/qemu-iotests/026 | 2 +- tests/qemu-iotests/026.out | 60 ++++++++++++-- tests/qemu-iotests/031.out | 23 +++--- tests/qemu-iotests/036 | 2 + tests/qemu-iotests/036.out | 7 +- tests/qemu-iotests/039 | 4 +- tests/qemu-iotests/061 | 2 + tests/qemu-iotests/061.out | 43 +++++----- tests/qemu-iotests/071 | 7 ++ tests/qemu-iotests/071.out | 4 + tests/qemu-iotests/089 | 2 +- tests/qemu-iotests/089.out | 2 - tests/qemu-iotests/091 | 2 +- tests/qemu-iotests/098 | 2 +- 28 files changed, 445 insertions(+), 111 deletions(-) -- 1.8.3.1
