SQPOLL fd close(2) question

SQPOLL fd close(2) question

[Josef]

Hi,

I implemented SQPOLL in netty for 5.8/5.9, to close a fd I need to
delete the entry first, it seems to fail with error -EADDRINUSE when I
remove the fd entry, close(2) it and the same socket(with the same
address) is created again,, is that known?
I assume that io_uring still has some reference to this, however
io_uring_unregister_files works fine but the drawback would be that I
need to wait until the ring is idle

example:
https://gist.github.com/1Jo1/53d01c4c2172bb0762b5dbcf9ef9c623

---
Josef

Re: SQPOLL fd close(2) question

[Jens Axboe]

On 9/25/20 10:21 AM, Josef wrote:
> Hi,
> 
> I implemented SQPOLL in netty for 5.8/5.9, to close a fd I need to
> delete the entry first, it seems to fail with error -EADDRINUSE when I
> remove the fd entry, close(2) it and the same socket(with the same
> address) is created again,, is that known?
> I assume that io_uring still has some reference to this, however
> io_uring_unregister_files works fine but the drawback would be that I
> need to wait until the ring is idle

If you have a file registered, that holds a reference to it. So when
you then otherwise close it in the app, it's similar to having done
a dup() on it and just closing the original. So yes, this is known and
expected, I'm afraid.

-- 
Jens Axboe

Re: SQPOLL fd close(2) question

[Josef]

> If you have a file registered, that holds a reference to it. So when
> you then otherwise close it in the app, it's similar to having done
> a dup() on it and just closing the original. So yes, this is known and
> expected, I'm afraid.

Thanks for clarification, the only way to delete the file registered
reference is to use io_uring_unregister_files right?
I don't think that we can support SQPOLL for 5.8/5.9, but at least for 5.10+ :)

---
Josef Grieb

Re: SQPOLL fd close(2) question

[Jens Axboe]

On 9/25/20 5:40 PM, Josef wrote:
>> If you have a file registered, that holds a reference to it. So when
>> you then otherwise close it in the app, it's similar to having done
>> a dup() on it and just closing the original. So yes, this is known and
>> expected, I'm afraid.
> 
> Thanks for clarification, the only way to delete the file registered
> reference is to use io_uring_unregister_files right?

Correct, that's the only way to trigger the final fput() that'll
close the socket (for real).

> I don't think that we can support SQPOLL for 5.8/5.9, but at least for 5.10+ :)

It'll be a lot more generically useful once we have non-registered file
support, so I'd probably just ignore it for now for your use case.

-- 
Jens Axboe