Re: [PATCH 2/2] io_uring: do not clamp read length for multishot read

[Jens Axboe <axboe@kernel.dk>]

On 11/6/23 8:33 AM, Dylan Yudaken wrote:
> On Mon, Nov 6, 2023 at 2:46?PM Jens Axboe <axboe@kernel.dk> 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