On Fri, Feb 14, 2025 at 01:59:20PM +0000, Daniel P. Berrangé wrote:
> On Fri, Feb 14, 2025 at 11:18:55AM +0100, Laurent Vivier wrote:
> > On 14/02/2025 11:06, Markus Armbruster wrote:
> > > Laurent Vivier <lviv...@redhat.com> writes:
> > >
> > > > The netdev reports NETDEV_VHOST_USER_CONNECTED event when
> > > > the chardev is connected, and NETDEV_VHOST_USER_DISCONNECTED
> > > > when it is disconnected.
> > > >
> > > > The NETDEV_VHOST_USER_CONNECTED event includes the ChardevInfo
> > > > (label, filename and frontend_open).
> > > >
> > > > This allows a system manager like libvirt to detect when the server
> > > > fails.
> > > >
> > > > For instance with passt:
> > > >
> > > > { 'execute': 'qmp_capabilities' }
> > > > { "return": { } }
> > > >
> > > > [killing passt here]
> > > >
> > > > { "timestamp": { "seconds": 1739517243, "microseconds": 115081 },
> > > > "event": "NETDEV_VHOST_USER_DISCONNECTED",
> > > > "data": { "netdev-id": "netdev0" } }
> > > >
> > > > [automatic reconnection with reconnect-ms]
> > > >
> > > > { "timestamp": { "seconds": 1739517290, "microseconds": 343777 },
> > > > "event": "NETDEV_VHOST_USER_CONNECTED",
> > > > "data": { "netdev-id": "netdev0",
> > > > "info": { "frontend-open": true,
> > > > "filename": "unix:",
> > > > "label": "chr0" } } }
> > > >
> > > > Signed-off-by: Laurent Vivier <lviv...@redhat.com>
> > >
> > > Standard question for events: if a management application misses an
> > > event, say because it restarts and reconnects, is there a way to obtain
> > > the missed information with a query command?
> > >
> >
> > query-chardev could help but it doesn't provide the netdev id.
>
> It doesn't have to IMHO. The application that created the NIC should know
> what ID it assigned to both the netdev and chardev, and thus should be
> able to use query-chardev to identify the chardev it previously
> associated with the netdev.
That said I kind of wonder whether we should be adding events against
the chardev directly, instead of against the netdev use of chardev.
ie CHARDEV_OPENED / CHARDEV_CLOSED events. For OPENED it is trivially
equivalent. For CLOSED it is a little trickier, since this patch does
delayed event dispatch from a bottom-half. If the chardev code was
able to emit this event from a bottom half itself, that could be OK
though.
With regards,
Daniel
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