netdev - Re: [PATCH v1 12/15] io_uring/zcrx: add io

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Message-ID: <177d164a-2ebc-483a-ab53-7741974a59c4@kernel.dk>
Date: Wed, 9 Oct 2024 13:42:21 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Pavel Begunkov <asml.silence@...il.com>, David Wei <dw@...idwei.uk>,
 io-uring@...r.kernel.org, netdev@...r.kernel.org
Cc: Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jesper Dangaard Brouer <hawk@...nel.org>, David Ahern <dsahern@...nel.org>,
 Mina Almasry <almasrymina@...gle.com>
Subject: Re: [PATCH v1 12/15] io_uring/zcrx: add io_recvzc request

On 10/9/24 1:27 PM, Pavel Begunkov wrote:
>>>>> +    /* All data completions are posted as aux CQEs. */
>>>>> +    req->flags |= REQ_F_APOLL_MULTISHOT;
>>>>
>>>> This puzzles me a bit...
>>>
>>> Well, it's a multishot request. And that flag protects from cq
>>> locking rules violations, i.e. avoiding multishot reqs from
>>> posting from io-wq.
>>
>> Maybe make it more like the others and require that
>> IORING_RECV_MULTISHOT is set then, and set it based on that?
> 
> if (IORING_RECV_MULTISHOT)
>     return -EINVAL;
> req->flags |= REQ_F_APOLL_MULTISHOT;
> 
> It can be this if that's the preference. It's a bit more consistent,
> but might be harder to use. Though I can just hide the flag behind
> liburing helpers, would spare from neverending GH issues asking
> why it's -EINVAL'ed

Maybe I'm missing something, but why not make it:

/* multishot required */
if (!(flags & IORING_RECV_MULTISHOT))
	return -EINVAL;
req->flags |= REQ_F_APOLL_MULTISHOT;

and yeah just put it in the io_uring_prep_recv_zc() or whatever helper.
That would seem to be a lot more consistent with other users, no?

>>>>> +    zc->flags = READ_ONCE(sqe->ioprio);
>>>>> +    zc->msg_flags = READ_ONCE(sqe->msg_flags);
>>>>> +    if (zc->msg_flags)
>>>>> +        return -EINVAL;
>>>>
>>>> Maybe allow MSG_DONTWAIT at least? You already pass that in anyway.
>>>
>>> What would the semantics be? The io_uring nowait has always
>>> been a pure mess because it's not even clear what it supposed
>>> to mean for async requests.
>>
>> Yeah can't disagree with that. Not a big deal, doesn't really matter,
>> can stay as-is.
> 
> I went through the MSG_* flags before looking which ones might
> even make sense here and be useful... Let's better enable if
> it'd be needed.

Yep that's fine.

-- 
Jens Axboe