From: Pavel Begunkov <asml.silence@gmail.com>
To: Constantine Gavrilov <constantine.gavrilov@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>,
io-uring@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH 1/2] io_uring: ensure recv and recvmsg handle MSG_WAITALL correctly
Date: Wed, 23 Mar 2022 20:52:21 +0000 [thread overview]
Message-ID: <fe48b17e-380f-7159-8c0c-d7c5208e61b2@gmail.com> (raw)
In-Reply-To: <CAAL3td3_VFmOH1mNXiG6geFeONSm066Xba5ePqPwkMr-zxkDGg@mail.gmail.com>
On 3/23/22 20:45, Constantine Gavrilov wrote:
> On Wed, Mar 23, 2022 at 10:14 PM Pavel Begunkov <asml.silence@gmail.com> wrote:
>>
>> On 3/23/22 15:39, Jens Axboe wrote:
>>> We currently don't attempt to get the full asked for length even if
>>> MSG_WAITALL is set, if we get a partial receive. If we do see a partial
>>> receive, then just note how many bytes we did and return -EAGAIN to
>>> get it retried.
>>>
>>> The iov is advanced appropriately for the vector based case, and we
>>> manually bump the buffer and remainder for the non-vector case.
>>
>> How datagrams work with MSG_WAITALL? I highly doubt it coalesces 2+
>> packets to satisfy the length requirement (e.g. because it may move
>> the address back into the userspace). I'm mainly afraid about
>> breaking io_uring users who are using the flag just to fail links
>> when there is not enough data in a packet.
>>
>> --
>> Pavel Begunkov
>
> Pavel:
>
> Datagrams have message boundaries and the MSG_WAITALL flag does not
> make sense there. I believe it is ignored by receive code on daragram
> sockets. MSG_WAITALL makes sends only on stream sockets, like TCP. The
> manual page says "This flag has no effect for datagram sockets.".
Missed the line this in mans, thanks, and it's exactly as expected.
The problem is on the io_uring side where with the patch it might
blindly do a second call into the network stack consuming 2+ packets.
--
Pavel Begunkov
next prev parent reply other threads:[~2022-03-23 20:53 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-23 15:39 [PATCHSET 0/2] Fix MSG_WAITALL for IORING_OP_RECV/RECVMSG Jens Axboe
2022-03-23 15:39 ` [PATCH 1/2] io_uring: ensure recv and recvmsg handle MSG_WAITALL correctly Jens Axboe
2022-03-23 20:13 ` Pavel Begunkov
2022-03-23 20:15 ` Jens Axboe
2022-03-23 20:45 ` Constantine Gavrilov
2022-03-23 20:52 ` Pavel Begunkov [this message]
2022-03-23 21:24 ` Jens Axboe
2022-03-23 15:39 ` [PATCH 2/2] io_uring: add flag for disabling provided buffer recycling Jens Axboe
-- strict thread matches above, loose matches on Subject: below --
2022-03-23 22:41 [PATCHSET v2 0/2] Fix MSG_WAITALL for IORING_OP_RECV/RECVMSG Jens Axboe
2022-03-23 22:41 ` [PATCH 1/2] io_uring: ensure recv and recvmsg handle MSG_WAITALL correctly Jens Axboe
2022-03-24 0:32 ` Stefan Metzmacher
2022-03-24 0:35 ` Jens Axboe
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