[Qemu-devel] [PATCH v8 0/7] vhost-user-blk: Add support for backend reconnecting

[elohimes]

From: Xie Yongji <address@hidden>

This patchset is aimed at supporting qemu to reconnect
vhost-user-blk backend after vhost-user-blk backend crash or
restart.

The patch 1,2,3 introduce started flag to VirtioDevice to
fix possible guest hung after migration for virtio 1.0
transitional devices.

The patch 4,5,6 support vhost-user-blk to reconnect backend
when connection closed.

The patch 7 introduces VHOST_USER_PROTOCOL_F_SLAVE_SHMFD
to vhost-user-blk backend which is used to tell qemu that
we support reconnecting now.

To use it, we could start qemu with:

qemu-system-x86_64 \
        -chardev socket,id=char0,path=/path/vhost.socket,reconnect=1, \
        -device vhost-user-blk-pci,chardev=char0 \

and start vhost-user-blk backend with:

vhost-user-blk -b /path/file -s /path/vhost.socket

Then we can restart vhost-user-blk at any time during VM running.

v8:
- Remove merged vhost-user part
- Introduce started flag to VirtioDevice to fix some bugs
- Rework reconnect logic in vhost_user_blk_device_realize()

v7:
- Introduce a 64-bit counter to struct DescStateSplit/DescStatePacked
  to preserve the order of fetching available descriptors
- Add support to resubmit inflight I/O in order in libvhost-user.c
- Rename process_head to last_batch_head in struct DescStateSplit

v6:
- Document the layout in inflight buffer for packed virtqueue
- Rework the layout in inflight buffer for split virtqueue
- Remove version field in VhostUserInflight
- Add a patch to remove some redundant check in
  contrib/libvhost-user.c
- Document more details in vhost-user.txt

v5:
- Drop patch that enables "nowait" option on client sockets
- Support resubmitting inflight I/O in order
- Make inflight I/O tracking more robust
- Remove align field and add queue size field in VhostUserInflight
- Document more details in vhost-user.txt

v4:
- Drop messages VHOST_USER_GET_SHM_SIZE and VHOST_USER_SET_SHM_FD
- Introduce two new messages VHOST_USER_GET_INFLIGHT_FD
  and VHOST_USER_SET_INFLIGHT_FD
- Allocate inflight buffer in backend rather than in qemu
- Document a recommended format for inflight buffer

v3:
- Using exisiting wait/nowait options to control connection on
  client sockets instead of introducing "disconnected" option.
- Support the case that vhost-user backend restart during initialzation
  of vhost-user-blk device.

v2:
- Introduce "disconnected" option for chardev instead of reuse "wait"
  option
- Support the case that QEMU starts before vhost-user backend
- Drop message VHOST_USER_SET_VRING_INFLIGHT
- Introduce two new messages VHOST_USER_GET_SHM_SIZE
  and VHOST_USER_SET_SHM_FD

Xie Yongji (7):
  virtio: Introduce started flag to VirtioDevice
  virtio: Use started flag in virtio_vmstate_change()
  vhost-user-blk: Use started flag in vhost_user_blk_set_status()
  vhost-user-blk: Only start vhost-user backend with the first kick
  vhost-user-blk: Add return value for vhost_user_blk_start()
  vhost-user-blk: Add support to reconnect backend
  contrib/vhost-user-blk: enable inflight I/O tracking

 contrib/vhost-user-blk/vhost-user-blk.c |   3 +-
 hw/block/vhost-user-blk.c               | 175 +++++++++++++++++++-----
 hw/virtio/virtio.c                      |  54 +++++++-
 include/hw/virtio/vhost-user-blk.h      |   3 +
 include/hw/virtio/virtio.h              |   2 +
 5 files changed, 202 insertions(+), 35 deletions(-)

-- 
2.17.1