Re: [PATCH bpf RFC-V3 1/5] xdp: rss hash types representation

[Jesper Dangaard Brouer]

On 30/03/2023 21.08, Jesper Dangaard Brouer wrote:
> On 30/03/2023 21.02, Stanislav Fomichev wrote:
> > On Thu, Mar 30, 2023 at 11:56 AM Jesper Dangaard Brouer
> > > On 30/03/2023 20.35, Stanislav Fomichev wrote:
> > > > On 03/30, Jesper Dangaard Brouer wrote:
> [...]
> > > [...]
> > > > > diff --git a/net/core/xdp.c b/net/core/xdp.c
> > > > > index 528d4b37983d..38d2dee16b47 100644
> > > > > --- a/net/core/xdp.c
> > > > > +++ b/net/core/xdp.c
> > > > > @@ -734,14 +734,22 @@ __bpf_kfunc int
> > > > > bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx, u64 *tim
> > > > >     * bpf_xdp_metadata_rx_hash - Read XDP frame RX hash.
> > > > >     * @ctx: XDP context pointer.
> > > > >     * @hash: Return value pointer.
> > > > > + * @rss_type: Return value pointer for RSS type.
> > > > > + *
> > > > > + * The RSS hash type (@rss_type) specifies what portion of packet 
> > > > > headers NIC
> > > > > + * hardware were used when calculating RSS hash value.  The type 
> > > > > combinations
> > > > > + * are defined via &enum xdp_rss_hash_type and individual bits can 
> > > > > be decoded
> > > > > + * via &enum xdp_rss_type_bits.
> > > > >     *
> > > > >     * Return:
> > > > >     * * Returns 0 on success or ``-errno`` on error.
> > > > >     * * ``-EOPNOTSUPP`` : means device driver doesn't implement kfunc
> > > > >     * * ``-ENODATA``    : means no RX-hash available for this frame
> > > > >     */
> > > > > -__bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx,
> > > > > u32 *hash)
> > > > > +__bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx,
> > > > > u32 *hash,
> > > > > +                     enum xdp_rss_hash_type *rss_type)
> > > > >    {
> > > > [..]
> > > >
> > > > > +    BTF_TYPE_EMIT(enum xdp_rss_type_bits);
> > > > nit: Do we still need this with an extra argument?
> > > Yes, unfortunately (compiler optimizes out enum xdp_rss_type_bits).
> > > Do notice the difference xdp_rss_type_bits vs xdp_rss_hash_type.
> > > We don't need it for "xdp_rss_hash_type" but need it for
> > > "xdp_rss_type_bits".
>  >
> > Ah, I missed that. Then why not expose xdp_rss_type_bits?
> > Keep xdp_rss_hash_type for internal drivers' tables, and export the
> > enum with the bits?
>
> Great suggestion, xdp_rss_hash_type will be internal for drivers.
> I will do that in V4.

I'm running into annoying compiler warnings [-Wenum-conversion]
about enum conversions.  I'll try to workaround this...
The easiest solution seem to be to only have a single enum, that both 
contains the BIT()s and combinations of bits (for driver usage).

E.g.
 warning: implicit conversion from 'enum xdp_rss_type_bits' to 'enum 
xdp_rss_hash_type' [-Wenum-conversion]