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

Jesper Dangaard Brouer
2023-03-30T19:09:27Z

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.

--Jesper