Re: [Qemu-devel] [PATCH for-4.0 0/6] vhost-user-blk: Add support for backend reconnecting

[Jason Wang]

On 2018/12/6 下午2:35, 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 tries to implenment the sync connection for
> "reconnect socket".
>
> The patch 2 introduces a new message VHOST_USER_SET_VRING_INFLIGHT
> to support offering shared memory to backend to record
> its inflight I/O.
>
> The patch 3,4 are the corresponding libvhost-user patches of
> patch 2. Make libvhost-user support VHOST_USER_SET_VRING_INFLIGHT.
>
> The patch 5 supports vhost-user-blk to reconnect backend when
> connection closed.
>
> The patch 6 tells 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,wait \
>          -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.


I wonder whether or not it's better to handle this at the level of 
virtio protocol itself instead of vhost-user level. E.g expose 
last_avail_idx to driver might be sufficient?

Another possible issue is, looks like you need to deal with different 
kinds of ring layouts e.g packed virtqueues.

Thanks


> Xie Yongji (6):
>    char-socket: Enable "wait" option for client mode
>    vhost-user: Add shared memory to record inflight I/O
>    libvhost-user: Introduce vu_queue_map_desc()
>    libvhost-user: Support recording inflight I/O in shared memory
>    vhost-user-blk: Add support for reconnecting backend
>    contrib/vhost-user-blk: enable inflight I/O recording
>
>   chardev/char-socket.c                   |   5 +-
>   contrib/libvhost-user/libvhost-user.c   | 215 ++++++++++++++++++++----
>   contrib/libvhost-user/libvhost-user.h   |  19 +++
>   contrib/vhost-user-blk/vhost-user-blk.c |   3 +-
>   hw/block/vhost-user-blk.c               | 169 +++++++++++++++++--
>   hw/virtio/vhost-user.c                  |  69 ++++++++
>   hw/virtio/vhost.c                       |   8 +
>   include/hw/virtio/vhost-backend.h       |   4 +
>   include/hw/virtio/vhost-user-blk.h      |   4 +
>   include/hw/virtio/vhost-user.h          |   8 +
>   10 files changed, 452 insertions(+), 52 deletions(-)