netdev - Re: [PATCH net-next 3/8] vhost-net: allow configuring extended features

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Message-ID: <CACGkMEsrPVYzva_EOHMnoqYWajqiRsMoXsfUrPfuimvG=8EKsQ@mail.gmail.com>
Date: Tue, 27 May 2025 11:56:18 +0800
From: Jason Wang <jasowang@...hat.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	"Michael S. Tsirkin" <mst@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Eugenio Pérez <eperezma@...hat.com>
Subject: Re: [PATCH net-next 3/8] vhost-net: allow configuring extended features

On Mon, May 26, 2025 at 6:57 PM Paolo Abeni <pabeni@...hat.com> wrote:
>
> On 5/26/25 2:47 AM, Jason Wang wrote:
> > On Wed, May 21, 2025 at 6:33 PM Paolo Abeni <pabeni@...hat.com> wrote:
> >>
> >> Use the extended feature type for 'acked_features' and implement
> >> two new ioctls operation to get and set the extended features.
> >>
> >> Note that the legacy ioctls implicitly truncate the negotiated
> >> features to the lower 64 bits range.
> >>
> >> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> >> ---
> >>  drivers/vhost/net.c        | 26 +++++++++++++++++++++++++-
> >>  drivers/vhost/vhost.h      |  2 +-
> >>  include/uapi/linux/vhost.h |  8 ++++++++
> >>  3 files changed, 34 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> >> index 7cbfc7d718b3f..b894685dded3e 100644
> >> --- a/drivers/vhost/net.c
> >> +++ b/drivers/vhost/net.c
> >> @@ -77,6 +77,10 @@ enum {
> >>                          (1ULL << VIRTIO_F_RING_RESET)
> >>  };
> >>
> >> +#ifdef VIRTIO_HAS_EXTENDED_FEATURES
> >> +#define VHOST_NET_FEATURES_EX VHOST_NET_FEATURES
> >> +#endif
> >> +
> >>  enum {
> >>         VHOST_NET_BACKEND_FEATURES = (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2)
> >>  };
> >> @@ -1614,7 +1618,7 @@ static long vhost_net_reset_owner(struct vhost_net *n)
> >>         return err;
> >>  }
> >>
> >> -static int vhost_net_set_features(struct vhost_net *n, u64 features)
> >> +static int vhost_net_set_features(struct vhost_net *n, virtio_features_t features)
> >>  {
> >>         size_t vhost_hlen, sock_hlen, hdr_len;
> >>         int i;
> >> @@ -1704,6 +1708,26 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
> >>                 if (features & ~VHOST_NET_FEATURES)
> >>                         return -EOPNOTSUPP;
> >>                 return vhost_net_set_features(n, features);
> >> +#ifdef VIRTIO_HAS_EXTENDED_FEATURES
> >
> > Vhost doesn't depend on virtio. But this invents a dependency, and I
> > don't understand why we need to do that.
>
> What do you mean with "dependency" here? vhost has already a build
> dependency vs virtio, including several virtio headers. It has also a
> logical dependency, using several virtio features.
>
> Do you mean a build dependency? this change does not introduce such a thing.

I mean vhost can be built without virtio drivers. So old vhost can run
new virtio drivers on top. So I don't see why vhost needs to check if
virtio of the same source tree supports 128 bit or not.

We can just accept an array of features now as

1) the changes are limited to vhost so it wouldn't be too much
2) we don't have to have VHOST_GET_FEATURES_EX2 in the future.

Thanks

>
> /P
>