This series adds for point-in-time snapshot NBD exporting based on blockdev-backup (variant of drive-backup with existing device as target). This patch is built on top of imain's sync mode patches for drive-backup.
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. (HMP) drive_add backing=ide0-hd0,file=BACKUP.qcow2,id=target0,if=none (where ide0-hd0 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=ide0-hd0 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-complete device=ide0-hd0 2. (HMP) drive_del target0 3. (SHELL) rm BACKUP.qcow2 v2: * Introduce soft and hard reference count, compared to a single type of ref count in v1. * Add "backing=" option to drive_add. * Introduce QMP command "blockdev-backup" Fam Zheng (11): block: replace in_use with refcnt_soft and refcnt_hard block: use refcnt for bs->backing_hd and bs->file block: use refcnt for drive_init/drive_uninit block: use refcnt for device attach/detach migration: omit drive ref as we have bdrv_ref now xen_disk: simplify blk_disconnect with refcnt block: hold hard reference for backup/mirror target block: simplify bdrv_drop_intermediate block: add assertion to check refcount before deleting block: add option 'backing' to -drive options qmp: add command 'blockdev-backup' block-migration.c | 6 +- block.c | 155 +++++++++++++++++++++------------------- block/backup.c | 3 +- block/blkdebug.c | 1 + block/blkverify.c | 1 + block/mirror.c | 4 +- block/snapshot.c | 2 +- block/stream.c | 2 +- block/vvfat.c | 1 + blockdev.c | 77 +++++++++++++++++++- blockjob.c | 6 +- hw/block/dataplane/virtio-blk.c | 4 +- hw/block/xen_disk.c | 7 +- include/block/block.h | 5 +- include/block/block_int.h | 3 +- qapi-schema.json | 49 +++++++++++++ qmp-commands.hx | 22 ++++++ 17 files changed, 248 insertions(+), 100 deletions(-) -- 1.8.3.2