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From: Jason Wang <jasowang@redhat.com>
Date: Fri, 31 May 2024 08:18:00 +0800
Message-ID: <CACGkMEsYRCJ96=sja9pBo_mnPsp75Go6E-wmm=-QX0kaOu4RFQ@mail.gmail.com>
Subject: Re: [PATCH net-next V2] virtio-net: synchronize operstate with admin
 state on up/down
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: xuanzhuo@linux.alibaba.com, eperezma@redhat.com, davem@davemloft.net, 
	edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, 
	virtualization@lists.linux.dev, netdev@vger.kernel.org, 
	linux-kernel@vger.kernel.org, 
	Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>, 
	Gia-Khanh Nguyen <gia-khanh.nguyen@oracle.com>
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On Thu, May 30, 2024 at 9:09=E2=80=AFPM Michael S. Tsirkin <mst@redhat.com>=
 wrote:
>
> On Thu, May 30, 2024 at 06:29:51PM +0800, Jason Wang wrote:
> > On Thu, May 30, 2024 at 2:10=E2=80=AFPM Michael S. Tsirkin <mst@redhat.=
com> 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 stat=
us
> > > > 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 DO=
WN 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 15=
00 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 DO=
WN 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 100=
0
> > > >     link/ether b2:a9:c5:04:da:53 brd ff:ff:ff:ff:ff:ff
> > > >
> > > > Cc: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
> > > > Cc: Gia-Khanh Nguyen <gia-khanh.nguyen@oracle.com>
> > > > Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > > Acked-by: Michael S. Tsirkin <mst@redhat.com>
> > > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > > ---
> > > > 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_enable=
d */
> > > > +     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.

For example, there could be a suspend/resume when the admin state is down.

>
>
> > 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.

Yes, but it should not matter much as it's done in the ndo_open().

Thanks

>
> --
> MST
>