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From: Jens Axboe <[email protected]>
To: Dylan Yudaken <[email protected]>
Cc: [email protected], [email protected]
Subject: Re: [PATCH 2/2] io_uring: do not clamp read length for multishot read
Date: Mon, 6 Nov 2023 08:46:58 -0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAO_Yeogr9D+MH2m4GGq40mKHfyvVgUscdPsjh2STi0Y2TZGNBQ@mail.gmail.com>

On 11/6/23 8:33 AM, Dylan Yudaken wrote:
> On Mon, Nov 6, 2023 at 2:46?PM Jens Axboe <[email protected]> wrote:
>>
>> On 11/5/23 3:30 PM, Dylan Yudaken wrote:
>>> When doing a multishot read, the code path reuses the old read
>>> paths. However this breaks an assumption built into those paths,
>>> namely that struct io_rw::len is available for reuse by __io_import_iovec.
>>>
>>> For multishot this results in len being set for the first receive
>>> call, and then subsequent calls are clamped to that buffer length incorrectly.
>>
>> Should we just reset this to 0 always in io_read_mshot()? And preferably
>> with a comment added as well as to why that is necessary to avoid
>> repeated clamping.
> 
> Unfortunately I don't think (without testing) that will work.
> Sometimes the request
> comes into io_read_mshot with the buffer already selected, and the
> length cannot
> be touched in that case.
> 
> We could check if the buffer is set, and if not clear the length I guess.
> I'm a bit unsure which is better - both seem equally ugly to be honest.

I mean do it at the end when we complete it, so it's reset for the next
iteration. But yeah, I'd want to have the test case verify this first
:-)

-- 
Jens Axboe


  reply	other threads:[~2023-11-06 15:47 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-11-05 22:30 [PATCH 0/2] io_uring: mshot read fix for buffer size changes Dylan Yudaken
2023-11-05 22:30 ` [PATCH 1/2] io_uring: do not allow multishot read to set addr or len Dylan Yudaken
2023-11-06 14:32   ` Jens Axboe
2023-11-06 14:51     ` Jens Axboe
2023-11-06 15:31       ` Dylan Yudaken
2023-11-05 22:30 ` [PATCH 2/2] io_uring: do not clamp read length for multishot read Dylan Yudaken
2023-11-06 14:46   ` Jens Axboe
2023-11-06 15:33     ` Dylan Yudaken
2023-11-06 15:46       ` Jens Axboe [this message]
2023-11-06 17:56         ` Jens Axboe
2023-11-06 20:35 ` [PATCH 0/2] io_uring: mshot read fix for buffer size changes Jens Axboe

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