Subject: Re: [PATCH net-next V2] virtio-net: synchronize operstate with admin state on up/down

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 30 May 2024 09:09:25 -0400

On Thu, May 30, 2024 at 06:29:51PM +0800, Jason Wang wrote:
> On Thu, May 30, 2024 at 2:10 PM Michael S. Tsirkin <[email-masked]> wrote:
> >
> > On Thu, May 30, 2024 at 11:20:55AM +0800, Jason Wang wrote:
> > > This patch synchronize operstate with admin state per RFC2863.
> > >
> > > This is done by trying to toggle the carrier upon open/close and
> > > synchronize with the config change work. This allows propagate status
> > > correctly to stacked devices like:
> > >
> > > ip link add link enp0s3 macvlan0 type macvlan
> > > ip link set link enp0s3 down
> > > ip link show
> > >
> > > Before this patch:
> > >
> > > 3: enp0s3: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
> > >     link/ether 00:00:05:00:00:09 brd ff:ff:ff:ff:ff:ff
> > > ......
> > > 5: macvlan0@enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
> > >     link/ether b2:a9:c5:04:da:53 brd ff:ff:ff:ff:ff:ff
> > >
> > > After this patch:
> > >
> > > 3: enp0s3: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
> > >     link/ether 00:00:05:00:00:09 brd ff:ff:ff:ff:ff:ff
> > > ...
> > > 5: macvlan0@enp0s3: <NO-CARRIER,BROADCAST,MULTICAST,UP,M-DOWN> mtu 1500 qdisc noqueue state LOWERLAYERDOWN mode DEFAULT group default qlen 1000
> > >     link/ether b2:a9:c5:04:da:53 brd ff:ff:ff:ff:ff:ff
> > >
> > > Cc: Venkat Venkatsubra <[email-masked]>
> > > Cc: Gia-Khanh Nguyen <[email-masked]>
> > > Reviewed-by: Xuan Zhuo <[email-masked]>
> > > Acked-by: Michael S. Tsirkin <[email-masked]>
> > > Signed-off-by: Jason Wang <[email-masked]>
> > > ---
> > > Changes since V1:
> > > - rebase
> > > - add ack/review tags
> >
> >
> >
> >
> >
> > > ---
> > >  drivers/net/virtio_net.c | 94 +++++++++++++++++++++++++++-------------
> > >  1 file changed, 63 insertions(+), 31 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 4a802c0ea2cb..69e4ae353c51 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -433,6 +433,12 @@ struct virtnet_info {
> > >       /* The lock to synchronize the access to refill_enabled */
> > >       spinlock_t refill_lock;
> > >
> > > +     /* Is config change enabled? */
> > > +     bool config_change_enabled;
> > > +
> > > +     /* The lock to synchronize the access to config_change_enabled */
> > > +     spinlock_t config_change_lock;
> > > +
> > >       /* Work struct for config space updates */
> > >       struct work_struct config_work;
> > >
> >
> >
> > But we already have dev->config_lock and dev->config_enabled.
> >
> > And it actually works better - instead of discarding config
> > change events it defers them until enabled.
> >
> 
> Yes but then both virtio-net driver and virtio core can ask to enable
> and disable and then we need some kind of synchronization which is
> non-trivial.

Well for core it happens on bring up path before driver works
and later on tear down after it is gone.
So I do not think they ever do it at the same time.

> And device enabling on the core is different from bringing the device
> up in the networking subsystem. Here we just delay to deal with the
> config change interrupt on ndo_open(). (E.g try to ack announce is
> meaningless when the device is down).
> 
> Thanks

another thing is that it is better not to re-read all config
on link up if there was no config interrupt - less vm exits.

-- 
MST