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From: David Laight <David.Laight@ACULAB.COM>
To: 'Aleksa Sarai' <cyphar@cyphar.com>,
	Josh Triplett <josh@joshtriplett.org>
Cc: "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"io-uring@vger.kernel.org" <io-uring@vger.kernel.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Arnd Bergmann <arnd@arndb.de>, Jens Axboe <axboe@kernel.dk>
Subject: RE: [PATCH v4 2/3] fs: openat2: Extend open_how to allow userspace-selected fds
Date: Sun, 19 Apr 2020 21:18:05 +0000	[thread overview]
Message-ID: <7f02bf52254443e380c33cae7c1fd5f0@AcuMS.aculab.com> (raw)
In-Reply-To: <20200419104404.j4e5gxdn2duvmu6s@yavin.dot.cyphar.com>

From: Aleksa Sarai
> Sent: 19 April 2020 11:44
> 
> On 2020-04-13, Josh Triplett <josh@joshtriplett.org> wrote:
> > Inspired by the X protocol's handling of XIDs, allow userspace to select
> > the file descriptor opened by openat2, so that it can use the resulting
> > file descriptor in subsequent system calls without waiting for the
> > response to openat2.
> >
> > In io_uring, this allows sequences like openat2/read/close without
> > waiting for the openat2 to complete. Multiple such sequences can
> > overlap, as long as each uses a distinct file descriptor.
> 
> I'm not sure I understand this explanation -- how can you trigger a
> syscall with an fd that hasn't yet been registered (unless you're just
> hoping the race goes in your favour)?

I suspect (there are no comments in the io_uring code to say what it does)
that the io_uring code uses a thread of the user process to sequentially
execute IO requests that the main application has added to a queue.

So it might make sense to queue up open/read/close.
But that ought to be within the io_uring code.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)


  reply	other threads:[~2020-04-19 21:18 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-14  2:14 [PATCH v4 0/3] Support userspace-selected fds Josh Triplett
2020-04-14  2:15 ` [PATCH v4 1/3] fs: Support setting a minimum fd for "lowest available fd" allocation Josh Triplett
2020-04-14  2:15 ` [PATCH v4 2/3] fs: openat2: Extend open_how to allow userspace-selected fds Josh Triplett
2020-04-19 10:44   ` Aleksa Sarai
2020-04-19 21:18     ` David Laight [this message]
2020-04-19 22:22     ` Jens Axboe
2020-04-20  2:06       ` Aleksa Sarai
2020-04-20 21:14     ` Josh Triplett
     [not found]   ` <f969e7d45a8e83efc1ca13d675efd8775f13f376.1586830316.git.josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org>
2020-04-27 13:52     ` [fs] ce436509a8: ltp.openat203.fail kernel test robot
2020-04-27 13:52       ` kernel test robot
2020-04-27 13:52       ` [LTP] " kernel test robot
2020-04-27 14:27       ` Cyril Hrubis
2020-04-27 14:27         ` Cyril Hrubis
2020-04-27 14:27         ` Cyril Hrubis
2020-04-28  0:51         ` Aleksa Sarai
2020-04-28  0:51           ` Aleksa Sarai
2020-04-28  0:51           ` Aleksa Sarai
2020-04-28 15:30           ` Cyril Hrubis
2020-04-28 15:30             ` Cyril Hrubis
2020-04-28 15:30             ` Cyril Hrubis
2020-04-28 15:30             ` Cyril Hrubis
2020-04-28 15:35             ` [LTP] " Aleksa Sarai
2020-04-28 15:35               ` Aleksa Sarai
2020-04-28 15:35               ` Aleksa Sarai
2020-04-14  2:16 ` [PATCH v4 3/3] fs: pipe2: Support O_SPECIFIC_FD Josh Triplett

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