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

[David Wei <dw@davidwei.uk>]

On 2025-02-21 17:07, Jens Axboe wrote:
> On 2/21/25 6:01 PM, Pavel Begunkov wrote:
>> On 2/22/25 00:08, Jens Axboe wrote:
>>> Just a few minor drive-by nits.
>>>
>>>> @@ -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;
>>>> +    /* UINT_MAX means no limit on readlen */
>>>> +    if (!zc->len)
>>>> +        zc->len = UINT_MAX;
>>>
>>> Why not just make UINT_MAX allowed, meaning no limit? Would avoid two
>>> branches here, and as far as I can tell not really change anything in
>>> terms of API niceness.
>>
>> I think 0 goes better as a special uapi value. It doesn't alter the
>> uapi, and commonly understood as "no limits", which is the opposite
>> to the other option, especially since UINT_MAX is not a max value for
>> an unlimited request, I'd easily expect it to drive more than 4GB.
> 
> Yeah that's certainly better, and as you say also has the same (forced)
> semantics for multishot.
> 

I thought about using 0 originally, but needed a way to distinguish 0
meaning no limit vs a limited read hitting 0 and completing. I could
store a flag in the request at recvzc_prep() time as an alternative.