Re: [Qemu-devel] [PATCH v2 22/23] vhost-user: wait until backend init is completed

["Marc-André Lureau" <mlureau@redhat.com>]

Hi

----- Original Message -----
> On Fri, Jun 24, 2016 at 03:51:09PM +0200, marcandre.lureau@redhat.com wrote:
> > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > 
> > The chardev waits for an initial connection before starting qemu,
> > vhost-user wants the backend negotiation to be completed. vhost-user is
> > started in the net_vhost_user_event callback, which is synchronously
> > called after the socket is connected.
> > 
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > ---
> >  net/vhost-user.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/vhost-user.c b/net/vhost-user.c
> > index 95ed2d2..4badd9e 100644
> > --- a/net/vhost-user.c
> > +++ b/net/vhost-user.c
> > @@ -24,6 +24,7 @@ typedef struct VhostUserState {
> >      VHostNetState *vhost_net;
> >      int watch;
> >      uint64_t acked_features;
> > +    bool started;
> >  } VhostUserState;
> >  
> >  typedef struct VhostUserChardevProps {
> > @@ -211,6 +212,7 @@ static void net_vhost_user_event(void *opaque, int
> > event)
> >              return;
> >          }
> >          qmp_set_link(name, true, &err);
> > +        s->started = true;
> >          break;
> >      case CHR_EVENT_CLOSED:
> >          qmp_set_link(name, false, &err);
> > @@ -248,7 +250,15 @@ static int net_vhost_user_init(NetClientState *peer,
> > const char *device,
> >          s->chr = chr;
> >      }
> >  
> > -    qemu_chr_add_handlers(chr, NULL, NULL, net_vhost_user_event,
> > nc[0].name);
> > +    do {
> > +        Error *err = NULL;
> > +        if (qemu_chr_wait_connected(chr, &err) < 0) {
> > +            error_report_err(err);
> > +            return -1;
> > +        }
> > +        qemu_chr_add_handlers(chr, NULL, NULL,
> > +                              net_vhost_user_event, nc[0].name);
> > +    } while (!s->started);
> 
> 
> I haven't looked at your patchset carefully yet, but I did a quick test,
> and showed that above code piece just breaks vhost-user: it's a dead loop
> that vhost-user net will be initiated again and again.

Interesting, thanks a lot for testing!

The vhost-user-test works just fine, as well as vhost-user-bridge.

> The dead loop is due to, we check "s->started" corresponding to last nc,
> while we set "s->started" corresponding to the first nc.

I see, that makes sense with multiqueue, I'll update the code. It would be really nice to have a basic multiqueue test in vhost-user-test.

thanks