Re: [RFC net-next PATCH 4/5] net: new XDP feature for reading HW rxhash from drivers

Jakub Kicinski
2017-05-20T04:13:38Z

On Fri, 19 May 2017 20:34:00 -0700, Alexei Starovoitov wrote:
> On Fri, May 19, 2017 at 08:21:47PM -0700, Jakub Kicinski wrote:
> > On Fri, 19 May 2017 20:07:52 -0700, Alexei Starovoitov wrote:
> > > How about exposing 'struct mlx5_cqe64 *' to XDP programs as-is?
> > > We can make sure that XDP program does read only access into it and
> > > it will see cqe->rss_hash_result, cqe->rss_hash_type and everything else
> > > in there, but this will not be uapi and it will be pretty obvious
> > > to program authors that their programs are vendor specific.
> > > 'not uapi' here means that mellanox is free to change their HW descriptor
> > > and its contents as they wish.
> >
> > Hm.. Would that mean we have to teach the verifier about all possible
> > drivers and their metadata structures (i.e. sizes thereof). And add an
> > UAPI enum of known drivers?
>
> why? no uapi other than a pointer to this hw rx descriptor.
> Different sizeof(hw_rx_descriptor) is not a problem.
> We deal with it already in tracing. All tracepoints have different
> sizeof(*ctx), yet the safety is preserved.

Ack, quick read of tracing code reveals this indeed should work.