Re: [PATCH v2 1/2] io_uring/zcrx: add single shot recvzc

[Pavel Begunkov <asml.silence@gmail.com>]

On 2/22/25 01:09, Jens Axboe wrote:
> On 2/21/25 6:06 PM, Pavel Begunkov wrote:
>> On 2/22/25 00:52, Jens Axboe wrote:
>>>>> @@ -1250,6 +1251,12 @@ int io_recvzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>>>>>         zc->ifq = req->ctx->ifq;
>>>>>         if (!zc->ifq)
>>>>>             return -EINVAL;
>>>>> +    zc->len = READ_ONCE(sqe->len);
>>>>> +    if (zc->len == UINT_MAX)
>>>>> +        return -EINVAL;
>>>>
>>>> The uapi gives u32, if we're using a special value it should
>>>> match the type. ~(u32)0
>>>
>>> Any syscall in Linux is capped at 2G anyway, so I think all of this
>>
>> I don't see how it related, you don't have to have a weird
>> 00111111b as a special value.
>>
>>> special meaning of ->len just needs to go away. Just ask for whatever
>>> bytes you want, but yes more than 2G will not be supported anyway.
>>
>> That's not the case here, the request does support more than 2G,
>> it's just spread across multiple CQEs, and the limit accounts
>> for multiple CQEs.
> 
> All pretty moot if we just go with 0 as the "transfer whatever length
> you want", as obviously each individual transfer will be limited anyway.
> Which is the better choice than having some odd 4G value.

I think so as well, and we'd need to check for 0 otherwise.
And it's probably fine to reserve a U32_MAX as above if it
has a chance to make (even if in the future) handling easier,
not like prep is performance sensitive.

-- 
Pavel Begunkov