[Qemu-devel] [PATCH v2 00/11] Point-in-time snapshot exporting over NBD

[Fam Zheng <famz@redhat.com>]

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