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

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Message-ID: <CACGkMEv9-GDayzA+HwY3g8+AT=0PDMQeWv_yx7wXAO96-+82sA@mail.gmail.com>
Date: Tue, 3 Jun 2025 10:11:24 +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 Thu, May 29, 2025 at 7:10 PM Paolo Abeni <pabeni@...hat.com> wrote:
>
> On 5/27/25 5:56 AM, Jason Wang wrote:
> > 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.
>
> AFAICS the ioctl() interface code wise only impacts on the device
> implementing extended features support, I guess it could be changed to
> to something alike:
>
> struct vhost_virtio_features {
>         __u64 count;
>         __u64 features[];
> };
>
> #define VHOST_GET_FEATURES_VECTOR _IOR(VHOST_VIRTIO, 0x83, struct
> vhost_virtio_features)
> #define VHOST_SET_FEATURES_VECTOR _IOW(VHOST_VIRTIO, 0x83, struct
> vhost_virtio_features)
>
> I could drop the above #ifdef, and the implementation would copy in/out
> only the known/supported number of features.
>
> WDYT?

This looks good.

Thanks

>
> /P
>