Re: io_uring file descriptor address already in use error

[Josef <josef.grieb@gmail.com>]

> In order for the patch to be able to move ahead, we'd need to be able
> to control this behavior. Right now we rely on the file being there if
> we need to repoll, see:
>
> commit a6ba632d2c249a4390289727c07b8b55eb02a41d
> Author: Jens Axboe <axboe@kernel.dk>
> Date:   Fri Apr 3 11:10:14 2020 -0600
>
>     io_uring: retry poll if we got woken with non-matching mask
>
> If this never happened, we would not need the file at all and we could
> make it the default behavior. But don't think that's solvable.
>
> > is there no other way around to close the file descriptor? Even if I
> > remove the poll, it doesn't work
>
> If you remove the poll it should definitely work, as nobody is holding a
> reference to it as you have nothing else in flight. Can you clarify what
> you mean here?
>
> I don't think there's another way, outside of having a poll (io_uring
> or poll(2), doesn't matter, the behavior is the same) being triggered in
> error. That doesn't happen, as mentioned if you do epoll/poll on a file
> and you close it, it won't trigger an event.
>
> > btw if understood correctly poll remove operation refers to all file
> > descriptors which arming a poll in the ring buffer right?
> > Is there a way to cancel a specific file descriptor poll?
>
> You can cancel specific requests by identifying them with their
> ->user_data. You can cancel a poll either with POLL_REMOVE or
> ASYNC_CANCEL, either one will find it. So as long as you have that, and
> it's unique, it'll only cancel that one specific request.

thanks it works, my bad, I was not aware that user_data is associated
with the poll request user_data...just need to remove my server socket
poll which binds to an address so I think this patch is not really
necessary

btw IORING_FEAT_FAST_POLL feature which arming poll for read events,
how does it work when the file descriptor(not readable yet) wants to
read(non blocking) something and I close(2) the file descriptor? I'm
guessing io_uring doesn't hold any reference to it anymore right?


---
Josef Grieb