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Re: [Qemu-devel] [PATCH 00/24] vhost-user reconnect fixes

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH 00/24] vhost-user reconnect fixes
Date: Sat, 25 Jun 2016 01:19:22 +0300

On Fri, Jun 24, 2016 at 03:22:19PM +0200, Marc-André Lureau wrote:
> Hi
> On Thu, Jun 23, 2016 at 6:31 AM, Michael S. Tsirkin <address@hidden> wrote:
> >
> > OK so if it's ok for read or write to fail, then I think
> > the callback should just return success.
> > This will make sure backends such as vhost net in kernel
> > where failure indicates an internal bug are handled
> > correctly, while vhost user ignores errors and attempts
> > to go on.
> >
> That's what we are trying to do, but since it's not yet well defined
> how to disconnect/reconnect and there are many bugs around this, it
> would help a lot to add error checking and error reporting for now.

Just for debugging?  OK, how about a macro with #ifdef DEBUG or
something like that then?

> >> Since there is feature checks on reconnection, qemu should wait for
> >> the initial connection feature negotiation to complete. The test added
> >> demonstrates this.
> >
> >
> > So on disconnect, we keep the guest going? But then when connect is
> > attempted, then we for some reason block guest until negotiation
> > is done? Sounds rather strange to me.
> When qemu is the server, it already waits for an initial connection
> from vhost-user backend. Here it is just enhanced to wait for the
> initial nego to complete, which is necessary for proper device
> initialization and also further reconnections checks.

OH, it's just for the initial connection? I didn't realize.
Will have to re-read it to figure it out. Some comments in commit log
and code pointing this out could also help.

> -- 
> Marc-André Lureau

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