netdev - Re: [PATCH net-next v2] virtio-net: ethtool configurable RXCSUM

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Message-ID: <CA+FuTSeVRhM+q_WuWvBDMk+Ao61y+iJWTukpoLzNCHGfYG9=UA@mail.gmail.com>
Date:   Fri, 9 Oct 2020 09:48:31 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Tonghao Zhang <xiangxia.m.yue@...il.com>
Cc:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Jason Wang <jasowang@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2] virtio-net: ethtool configurable RXCSUM

On Thu, Oct 8, 2020 at 9:19 PM Tonghao Zhang <xiangxia.m.yue@...il.com> wrote:
>
> On Wed, Sep 30, 2020 at 6:05 PM Willem de Bruijn
> <willemdebruijn.kernel@...il.com> wrote:
> >
> > On Wed, Sep 30, 2020 at 4:05 AM <xiangxia.m.yue@...il.com> wrote:
> > >
> > > From: Tonghao Zhang <xiangxia.m.yue@...il.com>
> > >
> > > Allow user configuring RXCSUM separately with ethtool -K,
> > > reusing the existing virtnet_set_guest_offloads helper
> > > that configures RXCSUM for XDP. This is conditional on
> > > VIRTIO_NET_F_CTRL_GUEST_OFFLOADS.
> > >
> > > If Rx checksum is disabled, LRO should also be disabled.
> > >
> > > Cc: Michael S. Tsirkin <mst@...hat.com>
> > > Cc: Jason Wang <jasowang@...hat.com>
> > > Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
> >
> > The first patch was merged into net.
> >
> > Please wait until that is merged into net-next, as this depends on the
> > other patch.
> >
> > > ---
> > > v2:
> > > * LRO depends the rx csum
> > > * remove the unnecessary check
> > > ---
> > >  drivers/net/virtio_net.c | 49 ++++++++++++++++++++++++++++++----------
> > >  1 file changed, 37 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 21b71148c532..5407a0106771 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -68,6 +68,8 @@ static const unsigned long guest_offloads[] = {
> > >                                 (1ULL << VIRTIO_NET_F_GUEST_ECN)  | \
> > >                                 (1ULL << VIRTIO_NET_F_GUEST_UFO))
> > >
> > > +#define GUEST_OFFLOAD_CSUM_MASK (1ULL << VIRTIO_NET_F_GUEST_CSUM)
> > > +
> > >  struct virtnet_stat_desc {
> > >         char desc[ETH_GSTRING_LEN];
> > >         size_t offset;
> > > @@ -2522,29 +2524,49 @@ static int virtnet_get_phys_port_name(struct net_device *dev, char *buf,
> > >         return 0;
> > >  }
> > >
> > > +static netdev_features_t virtnet_fix_features(struct net_device *netdev,
> > > +                                             netdev_features_t features)
> > > +{
> > > +       /* If Rx checksum is disabled, LRO should also be disabled.
> > > +        * That is life. :)
> >
> > Please remove this second line.
> OK
> > > +        */
> > > +       if (!(features & NETIF_F_RXCSUM))
> > > +               features &= ~NETIF_F_LRO;
> > > +
> > > +       return features;
> > > +}
> > > +
> > >  static int virtnet_set_features(struct net_device *dev,
> > >                                 netdev_features_t features)
> > >  {
> > >         struct virtnet_info *vi = netdev_priv(dev);
> > > -       u64 offloads;
> > > +       u64 offloads = vi->guest_offloads &
> > > +                      vi->guest_offloads_capable;
> >
> > When can vi->guest_offloads have bits set outside the mask of
> > vi->guest_offloads_capable?
> In this case, we can use only vi->guest_offloads. and
> guest_offloads_capable will not be used any more.
> so should we remove guest_offloads_capable ?

That bitmap stores the capabilities of the device as learned at
initial device probe. I don't see how it can be removed.