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From: Stefan Metzmacher <[email protected]>
To: Jens Axboe <[email protected]>
Cc: io-uring <[email protected]>,
	Linus Torvalds <[email protected]>,
	Samba Technical <[email protected]>
Subject: Re: Problems replacing epoll with io_uring in tevent
Date: Thu, 27 Oct 2022 21:54:45 +0200	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

Hi Jens,

>> I'm currently trying to prototype for an IORING_POLL_CANCEL_ON_CLOSE
>> flag that can be passed to POLL_ADD. With that we'll register
>> the request in &req->file->f_uring_poll (similar to the file->f_ep list for epoll)
>> Then we only get a real reference to the file during the call to
>> vfs_poll() otherwise we drop the fget/fput reference and rely on
>> an io_uring_poll_release_file() (similar to eventpoll_release_file())
>> to cancel our registered poll request.
> 
> Yes, this is a bit tricky as we hold the file ref across the operation. I'd
> be interested in seeing your approach to this, and also how it would
> interact with registered files...

It should work fine with fixed files, but I haven't tested it.

But from reading the code I'm wondering what happens in general with pending
requests on a closed fixed file? There's no referencing in io_file_get_fixed(),
or is it done via io_req_set_rsrc_node() together with the
io_rsrc_node_switch_start()/io_queue_rsrc_removal()/io_rsrc_node_switch()
within io_fixed_fd_remove()?

But IORING_POLL_CANCEL_ON_CLOSE doesn't have any effect together with
REQ_F_FIXED_FILE (in my current code). Maybe a io_fixed_fd_remove()
should call __io_async_cancel with IORING_ASYNC_CANCEL_FD_FIXED.

I was also thinking if any pending could be canceled by a close(),
because they all have the registered in the struct file list...
But that might be overkill and io_uring aware applications can just use
IORING_ASYNC_CANCEL_FD_* explicitly. Also fixed files are also only
used by io_uring aware code.

metze

      parent reply	other threads:[~2022-10-27 19:54 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-18 14:42 Problems replacing epoll with io_uring in tevent Stefan Metzmacher
2022-10-26 16:00 ` Stefan Metzmacher
2022-10-26 17:08   ` Jens Axboe
2022-10-26 17:41     ` Pavel Begunkov
2022-10-27  8:18       ` Stefan Metzmacher
2022-10-27  8:05     ` Stefan Metzmacher
2022-10-27 19:25       ` Stefan Metzmacher
2022-12-28 16:19         ` Stefan Metzmacher
2023-01-18 15:56           ` Jens Axboe
2023-02-01 20:29             ` Stefan Metzmacher
2022-10-27  8:51     ` Stefan Metzmacher
2022-10-27 12:12       ` Jens Axboe
2022-10-27 18:35         ` Stefan Metzmacher
2022-10-27 19:54     ` Stefan Metzmacher [this message]

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