Re: [PATCH net-next v10 3/9] net: devmem: TCP tx netlink api

[Mina Almasry <almasrymina@google.com>]

On Wed, Apr 23, 2025 at 5:11 AM Donald Hunter <donald.hunter@gmail.com> wrote:
>
> Mina Almasry <almasrymina@google.com> writes:
>
> > From: Stanislav Fomichev <sdf@fomichev.me>
> >
> > Add bind-tx netlink call to attach dmabuf for TX; queue is not
> > required, only ifindex and dmabuf fd for attachment.
> >
> > Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
> > Signed-off-by: Mina Almasry <almasrymina@google.com>
> >
> > ---
> >
> > v3:
> > - Fix ynl-regen.sh error (Simon).
> >
> > ---
> >  Documentation/netlink/specs/netdev.yaml | 12 ++++++++++++
> >  include/uapi/linux/netdev.h             |  1 +
> >  net/core/netdev-genl-gen.c              | 13 +++++++++++++
> >  net/core/netdev-genl-gen.h              |  1 +
> >  net/core/netdev-genl.c                  |  6 ++++++
> >  tools/include/uapi/linux/netdev.h       |  1 +
> >  6 files changed, 34 insertions(+)
> >
> > diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
> > index f5e0750ab71db..c0ef6d0d77865 100644
> > --- a/Documentation/netlink/specs/netdev.yaml
> > +++ b/Documentation/netlink/specs/netdev.yaml
> > @@ -743,6 +743,18 @@ operations:
> >              - defer-hard-irqs
> >              - gro-flush-timeout
> >              - irq-suspend-timeout
> > +    -
> > +      name: bind-tx
> > +      doc: Bind dmabuf to netdev for TX
>
> nit: maybe add "for RX" to the bind-rx doc.
>

Thanks, will pull this with the next iteration.

> > +      attribute-set: dmabuf
>
> The bind-rx op has "flags: [ admin-perm ]", should bind-tx also?
>

The omission of admin-perm for tx is intentional.

Binding a dmabuf to an rx queue should and is a privileged operation,
because basically the application doing the binding is taking
ownership of this rx queue. For TX, no such queue ownership is being
taken. The TX binding just gives the netdevice access to the dmabuf
dma-addresses so the netdevice can send from there. It's very similar
to a normal dma-map with normal memory. There is no need for privilege
checks.

-- 
Thanks,
Mina