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From: Stefan Metzmacher <metze@samba.org>
To: Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org
Cc: jlayton@kernel.org, josh@joshtriplett.org
Subject: Re: [PATCHSET v2 0/6] Support selectable file descriptors
Date: Mon, 9 Mar 2020 21:33:21 +0100	[thread overview]
Message-ID: <f8cb2b65-fc97-5c46-67e0-5624385daedc@samba.org> (raw)
In-Reply-To: <20200304180016.28212-1-axboe@kernel.dk>


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Hi Jens,

> One of the fabled features with chains has long been the desire to
> support things like:
> 
> <open fileX><read from fileX><close fileX>
> 
> in a single chain. This currently doesn't work, since the read/close
> depends on what file descriptor we get on open.
> 
> The original attempt at solving this provided a means to pass
> descriptors between chains in a link, this version takes a different
> route. Based on Josh's support for O_SPECIFIC_FD, we can instead control
> what fd value we're going to get out of open (or accept). With that in
> place, we don't need to do any magic to make this work. The above chain
> then becomes:
> 
> <open fileX with fd Y><read from fd Y><close fd Y>
> 
> which is a lot more useful, and allows any sort of weird chains without
> needing to nest "last open" file descriptors.

I like that approach, however I'm wondering if this able to be used by
libraries as it requires coordination of fd values within the whole
process. I don't think this would be a reason to block that feature,
but it might be good to be added to the manpages.

As future addition I'd like to get support for something similar
but for io_uring fixed file slots. That could also be used by libraries
using a private ring fd.

metze


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      parent reply	other threads:[~2020-03-09 20:33 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-04 18:00 [PATCHSET v2 0/6] Support selectable file descriptors Jens Axboe
2020-03-04 18:00 ` [PATCH 1/6] fs: openat2: Extend open_how to allow userspace-selected fds Jens Axboe
2020-03-04 18:00 ` [PATCH 2/6] io_uring: move CLOSE req->file checking into handler Jens Axboe
2020-03-04 18:00 ` [PATCH 3/6] io_uring: move read/write side file based prep into op handler Jens Axboe
2020-03-04 18:00 ` [PATCH 4/6] io_uring: support deferred retrival of file from fd Jens Axboe
2020-03-04 18:00 ` [PATCH 5/6] net: allow specific fd selection for __sys_accept4_file() Jens Axboe
2020-03-04 18:00 ` [PATCH 6/6] io_uring: allow specific fd for IORING_OP_ACCEPT Jens Axboe
2020-03-04 19:02   ` Josh Triplett
2020-03-04 19:09     ` Jens Axboe
2020-03-04 19:51       ` Josh Triplett
2020-03-04 19:03 ` [PATCHSET v2 0/6] Support selectable file descriptors Josh Triplett
2020-03-04 19:10   ` Jens Axboe
2020-03-04 19:28     ` Jeff Layton
2020-03-04 19:50       ` Jens Axboe
2020-03-04 19:56     ` Josh Triplett
2020-03-04 20:00       ` Jens Axboe
2020-03-04 20:09         ` Josh Triplett
2020-03-04 20:14           ` Jens Axboe
2020-03-09 20:33 ` Stefan Metzmacher [this message]

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