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

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Date:   Fri, 31 Mar 2023 13:49:15 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Stanislav Fomichev <sdf@...gle.com>,
        Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     brouer@...hat.com, bpf@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, martin.lau@...nel.org,
        ast@...nel.org, daniel@...earbox.net, alexandr.lobakin@...el.com,
        larysa.zaremba@...el.com, xdp-hints@...-project.net,
        anthony.l.nguyen@...el.com, yoong.siang.song@...el.com,
        boon.leong.ong@...el.com, intel-wired-lan@...ts.osuosl.org,
        pabeni@...hat.com, jesse.brandeburg@...el.com, kuba@...nel.org,
        edumazet@...gle.com, john.fastabend@...il.com, hawk@...nel.org,
        davem@...emloft.net
Subject: Re: [PATCH bpf RFC-V3 1/5] xdp: rss hash types representation


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]