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


From: Jason Wang
Subject: Re: [Qemu-devel] [PATCH v5 0/6] vhost-user-blk: Add support for backend reconnecting
Date: Wed, 30 Jan 2019 10:29:10 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0


On 2019/1/22 下午4:31, address@hidden wrote:
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 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


I'm still not convinced about this approach. If the maintainer decide to merge, at least two things needs to be added besides the correctness of the code:

- you need prove that this approach can work for packed ring

-  an unit-test to test the crash during logging in-flight descriptor.

Thanks



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(-)




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