Re: [PATCHSET 0/3] io_uring: make POLL_ADD support multiple waitqs

[Jens Axboe <axboe@kernel.dk>]

On 2/11/20 1:01 PM, Pavel Begunkov wrote:
> On 10/02/2020 23:56, Jens Axboe wrote:
>> As mentioned in the previous email, here are the three patches that add
>> support for multiple waitqueues for polling with io_uring.
>>
>> Patches 1-2 are just basic prep patches, and should not have any
>> functional changes in them. Patch 3 adds support for allocating a new
>> io_poll_iocb unit if we get multiple additions through our queue proc
>> for the wait queues. This new 'poll' addition is queued up as well, and
>> it grabs a reference to the original poll request.
>>
>> Please do review, would love to get this (long standing) issue fixed as
>> it's a real problem for various folks.
>>
> 
> I need to dig a bit deeper into poll to understand some moments, but there is a
> question: don't we won't to support arbitrary number of waitqueues then?

In theory, probably. But in practice, don't think anything exists with > 2
waitqueues. As mentioned, even the 2 waitqueue case is limited to less than
a handful of users.

But the patch should for sure check this, and -EINVAL if we get a third
entry attempted.

-- 
Jens Axboe