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From: Yongji Xie <elohimes@gmail.com>
Date: Thu, 6 Dec 2018 15:43:00 +0800
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Subject: Re: [Qemu-devel] [PATCH for-4.0 0/6] vhost-user-blk: Add support
 for backend reconnecting
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To: marcandre.lureau@gmail.com
Cc: "Michael S. Tsirkin" <mst@redhat.com>, nixun@baidu.com, qemu-devel@nongnu.org, lilin24@baidu.com, zhangyu31@baidu.com, chaiwen@baidu.com, Xie Yongji <xieyongji@baidu.com>

On Thu, 6 Dec 2018 at 15:23, Marc-Andr=C3=A9 Lureau
<marcandre.lureau@gmail.com> wrote:
>
> Hi
>
> On Thu, Dec 6, 2018 at 10:36 AM <elohimes@gmail.com> wrote:
> >
> > 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 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=3Dchar0,path=3D/path/vhost.socket,reconnect=
=3D1,wait \
> >         -device vhost-user-blk-pci,chardev=3Dchar0 \
>
> Why do you want qemu to be the client since it is actually the one
> that serves and remains alive?  Why make it try to reconnect regularly
> when it could instead wait for a connection to come up?
>

Actually, this patchset should also work when qemu is in server mode.
The reason I make qemu to be client is that some vhost-user backend
such as spdk, vhost-user-blk may still work in server mode. And
seems like we could not make sure all vhost-user backend is working in
client mode.

Thanks,
Yongji