[Qemu-devel] [PATCH v5 0/6] vhost-user-blk: Add support for backend reconnecting

[elohimes@gmail.com]

From: Xie Yongji <xieyongji@baidu.com>

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

The patch 1 introduces two new messages VHOST_USER_GET_INFLIGHT_FD
and VHOST_USER_SET_INFLIGHT_FD to support support transferring shared
buffer between qemu and backend.

The patch 2,3 are the corresponding libvhost-user patches of
patch 1. Make libvhost-user support VHOST_USER_GET_INFLIGHT_FD
and VHOST_USER_SET_INFLIGHT_FD.

The patch 4 allows vhost-user-blk to use the two new messages
to get/set inflight buffer from/to backend.

The patch 5 supports vhost-user-blk to reconnect backend when
connection closed.

The patch 6 introduces VHOST_USER_PROTOCOL_F_SLAVE_SHMFD
to vhost-user-blk backend which is used to tell qemu that
we support reconnecting now.

This series is based on Daniel P. Berrangé's patchset:

https://lists.gnu.org/archive/html/qemu-devel/2019-01/msg03344.html

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.

V4 to 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

V3 to 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

V2 to 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.

V1 to 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 (6):
  vhost-user: Support transferring inflight buffer between qemu and
    backend
  libvhost-user: Introduce vu_queue_map_desc()
  libvhost-user: Support tracking inflight I/O in shared memory
  vhost-user-blk: Add support to get/set inflight buffer
  vhost-user-blk: Add support to reconnect backend
  contrib/vhost-user-blk: enable inflight I/O tracking

 Makefile                                |   2 +-
 contrib/libvhost-user/libvhost-user.c   | 402 ++++++++++++++++++++----
 contrib/libvhost-user/libvhost-user.h   |  40 +++
 contrib/vhost-user-blk/vhost-user-blk.c |   3 +-
 docs/interop/vhost-user.txt             | 101 ++++++
 hw/block/vhost-user-blk.c               | 227 ++++++++++---
 hw/virtio/vhost-user.c                  | 110 +++++++
 hw/virtio/vhost.c                       | 105 +++++++
 include/hw/virtio/vhost-backend.h       |  10 +
 include/hw/virtio/vhost-user-blk.h      |   5 +
 include/hw/virtio/vhost.h               |  19 ++
 11 files changed, 925 insertions(+), 99 deletions(-)

-- 
2.17.1