This series adds for point-in-time snapshot NBD exporting based on blockdev-backup (variant of drive-backup with existing device as target).
We get a thin point-in-time snapshot by COW mechanism of drive-backup, and export it through built in NBD server. The steps are as below: 1. (SHELL) qemu-img create -f qcow2 BACKUP.qcow2 <source size here> (Alternatively we can use -o backing_file=RUNNING-VM.img to omit explicitly providing the size by ourselves, but it's risky because RUNNING-VM.qcow2 is used r/w by guest. Whether or not setting backing file in the image file doesn't matter, as we are going to override the backing hd in the next step) 2. (QMP) blockdev-add backing=source-drive file.driver=file file.filename=BACKUP.qcow2 id=target0 if=none driver=qcow2 (where source-drive is the running BlockDriverState name for RUNNING-VM.img. This patch implements "backing=" option to override backing_hd for added drive) 3. (QMP) blockdev-backup device=source-drive sync=none target=target0 (this is the QMP command introduced by this series, which use a named device as target of drive-backup) 4. (QMP) nbd-server-add device=target0 When image fleecing done: 1. (QMP) block-job-cancel device=source-drive 2. (HMP) drive_del target0 3. (SHELL) rm BACKUP.qcow2 v15: Rebase onto Kevin's PULL request. Add Benoit's rev-by for 1~4. Address Jeff's comments (thanks for reviewing!): [05/14] block: Add bdrv_set_backing_hd() bdrv_ref new backing before bdrv_unref the old one. Fix refcnt of backing_hd in bdrv_open_backing_file. Use bdrv_set_backing_hd in bdrv_append. [06/14] block: Add backing_blocker in BlockDriverState Fix mirror. [07/14] block: Parse "backing" option to reference existing BDS [08/14] block: Support dropping active in bdrv_drop_intermediate Avoid bdrv_swap for middle change. Fix comment. Fix commit by finding overlay before dropping intermediate. [14/14] qemu-iotests: Image fleecing test case 083 Rename 081 -> 083. Fam Zheng (14): block: Add BlockOpType enum block: Introduce op_blockers to BlockDriverState block: Replace in_use with operation blocker block: Move op_blocker check from block_job_create to its caller block: Add bdrv_set_backing_hd() block: Add backing_blocker in BlockDriverState block: Parse "backing" option to reference existing BDS block: Support dropping active in bdrv_drop_intermediate stream: Use bdrv_drop_intermediate and drop close_unused_images qmp: Add command 'blockdev-backup' block: Allow backup on referenced named BlockDriverState block: Add blockdev-backup to transaction qemu-iotests: Test blockdev-backup in 055 qemu-iotests: Image fleecing test case 083 block-migration.c | 7 +- block.c | 313 ++++++++++++++++++++++++++-------------- block/backup.c | 26 ++++ block/commit.c | 2 +- block/mirror.c | 1 + block/stream.c | 30 +--- blockdev.c | 118 +++++++++++++-- blockjob.c | 14 +- hw/block/dataplane/virtio-blk.c | 19 ++- include/block/block.h | 29 +++- include/block/block_int.h | 9 +- include/block/blockjob.h | 3 + qapi-schema.json | 50 +++++++ qmp-commands.hx | 44 ++++++ tests/qemu-iotests/055 | 275 +++++++++++++++++++++++++++++------ tests/qemu-iotests/055.out | 4 +- tests/qemu-iotests/083 | 99 +++++++++++++ tests/qemu-iotests/083.out | 5 + tests/qemu-iotests/group | 1 + 19 files changed, 844 insertions(+), 205 deletions(-) create mode 100755 tests/qemu-iotests/083 create mode 100644 tests/qemu-iotests/083.out -- 1.8.5.4