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

[Dylan Yudaken <dyudaken@gmail.com>]

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.