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From: Jens Axboe <axboe@kernel.dk>
To: Pavel Begunkov <asml.silence@gmail.com>,
	Hao Xu <haoxu@linux.alibaba.com>
Cc: io-uring@vger.kernel.org, Joseph Qi <joseph.qi@linux.alibaba.com>
Subject: Re: [PATCH 6/6] io_uring: enable multishot mode for accept
Date: Sun, 5 Sep 2021 13:44:50 -0600	[thread overview]
Message-ID: <f332dbc6-5304-9676-ffc1-008e153d667b@kernel.dk> (raw)
In-Reply-To: <701e50f5-2444-5b56-749b-1c1affc26ce9@gmail.com>

On 9/4/21 4:46 PM, Pavel Begunkov wrote:
> On 9/4/21 7:40 PM, Jens Axboe wrote:
>> On 9/4/21 9:34 AM, Hao Xu wrote:
>>> 在 2021/9/4 上午12:29, Jens Axboe 写道:
>>>> On 9/3/21 5:00 AM, Hao Xu wrote:
>>>>> Update io_accept_prep() to enable multishot mode for accept operation.
>>>>>
>>>>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>>>>> ---
>>>>>   fs/io_uring.c | 14 ++++++++++++--
>>>>>   1 file changed, 12 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>>>> index eb81d37dce78..34612646ae3c 100644
>>>>> --- a/fs/io_uring.c
>>>>> +++ b/fs/io_uring.c
>>>>> @@ -4861,6 +4861,7 @@ static int io_recv(struct io_kiocb *req, unsigned int issue_flags)
>>>>>   static int io_accept_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>>>>>   {
>>>>>   	struct io_accept *accept = &req->accept;
>>>>> +	bool is_multishot;
>>>>>   
>>>>>   	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
>>>>>   		return -EINVAL;
>>>>> @@ -4872,14 +4873,23 @@ static int io_accept_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>>>>>   	accept->flags = READ_ONCE(sqe->accept_flags);
>>>>>   	accept->nofile = rlimit(RLIMIT_NOFILE);
>>>>>   
>>>>> +	is_multishot = accept->flags & IORING_ACCEPT_MULTISHOT;
>>>>> +	if (is_multishot && (req->flags & REQ_F_FORCE_ASYNC))
>>>>> +		return -EINVAL;
>>>>
>>>> I like the idea itself as I think it makes a lot of sense to just have
>>>> an accept sitting there and generating multiple CQEs, but I'm a bit
>>>> puzzled by how you pass it in. accept->flags is the accept4(2) flags,
>>>> which can currently be:
>>>>
>>>> SOCK_NONBLOCK
>>>> SOCK_CLOEXEC
>>>>
>>>> While there's not any overlap here, that is mostly by chance I think. A
>>>> cleaner separation is needed here, what happens if some other accept4(2)
>>>> flag is enabled and it just happens to be the same as
>>>> IORING_ACCEPT_MULTISHOT?
>>> Make sense, how about a new IOSQE flag, I saw not many
>>> entries left there.
>>
>> Not quite sure what the best approach would be... The mshot flag only
>> makes sense for a few request types, so a bit of a shame to have to
>> waste an IOSQE flag on it. Especially when the flags otherwise passed in
>> are so sparse, there's plenty of bits there.
>>
>> Hence while it may not be the prettiest, perhaps using accept->flags is
>> ok and we just need some careful code to ensure that we never have any
>> overlap.
> 
> Or we can alias with some of the almost-never-used fields like
> ->ioprio or ->buf_index.

It's not a bad idea, as long as we can safely use flags from eg ioprio
for cases where ioprio would never be used. In that sense it's probably
safer than using buf_index.

The alternative is, as has been brougt up before, adding a flags2 and
reserving the last flag in ->flags to say "there are flags in flags2".
Not exactly super pretty either, but we'll need to extend them at some
point.

-- 
Jens Axboe


  parent reply	other threads:[~2021-09-05 19:44 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-03 11:00 [RFC 0/6] fast poll multishot mode Hao Xu
2021-09-03 11:00 ` [PATCH 1/6] io_uring: enhance flush completion logic Hao Xu
2021-09-03 11:42   ` Pavel Begunkov
2021-09-03 12:08     ` Hao Xu
2021-09-03 12:27       ` Pavel Begunkov
2021-09-03 13:38         ` Hao Xu
2021-09-17 18:49           ` Hao Xu
2021-09-03 11:00 ` [PATCH 2/6] io_uring: add IORING_ACCEPT_MULTISHOT for accept Hao Xu
2021-09-03 11:00 ` [PATCH 3/6] io_uring: add REQ_F_APOLL_MULTISHOT for requests Hao Xu
2021-09-03 11:00 ` [PATCH 4/6] io_uring: let fast poll support multishot Hao Xu
2021-09-06 15:56   ` Pavel Begunkov
2021-09-06 17:40     ` Hao Xu
2021-09-06 19:09       ` Pavel Begunkov
2021-09-07  6:38         ` Hao Xu
2021-09-06 19:04   ` Pavel Begunkov
2021-09-07  6:48     ` Hao Xu
2021-09-08 11:21       ` Hao Xu
2021-09-08 12:03         ` Pavel Begunkov
2021-09-08 13:13           ` Pavel Begunkov
2021-09-09  7:01           ` Hao Xu
2021-09-09  8:29             ` Hao Xu
2021-09-11 10:49               ` Pavel Begunkov
2021-09-11 20:19                 ` Hao Xu
2021-09-03 11:00 ` [PATCH 5/6] io_uring: implement multishot mode for accept Hao Xu
2021-09-04 22:39   ` Pavel Begunkov
2021-09-04 22:40     ` Pavel Begunkov
2021-09-06 15:34       ` Pavel Begunkov
2021-09-03 11:00 ` [PATCH 6/6] io_uring: enable " Hao Xu
2021-09-03 16:29   ` Jens Axboe
2021-09-04 15:34     ` Hao Xu
2021-09-04 18:40       ` Jens Axboe
2021-09-04 22:46         ` Pavel Begunkov
2021-09-05  7:29           ` Hao Xu
2021-09-05 19:44           ` Jens Axboe [this message]
2021-09-06  8:26             ` Hao Xu
2021-09-06  8:28               ` Hao Xu
2021-09-06 13:24               ` Jens Axboe
2021-09-06 12:35             ` Hao Xu
2021-09-06 13:31               ` Jens Axboe
2021-09-06 15:00                 ` Hao Xu
2021-09-06 15:32               ` Pavel Begunkov
2021-09-06 16:42                 ` Jens Axboe
2021-09-04 22:43   ` Pavel Begunkov
2021-09-05  6:25     ` Hao Xu
2021-09-05  8:27       ` Pavel Begunkov
2021-09-03 11:02 ` [RFC 0/6] fast poll multishot mode Hao Xu

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