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From: Josh Triplett <[email protected]>
To: Miklos Szeredi <[email protected]>
Cc: Michael Kerrisk <[email protected]>,
	[email protected],
	"[email protected]" <[email protected]>,
	lkml <[email protected]>,
	Alexander Viro <[email protected]>,
	Arnd Bergmann <[email protected]>, Jens Axboe <[email protected]>,
	Aleksa Sarai <[email protected]>,
	linux-man <[email protected]>,
	Linux API <[email protected]>
Subject: Re: [PATCH v5 2/3] fs: openat2: Extend open_how to allow userspace-selected fds
Date: Wed, 22 Apr 2020 17:48:07 -0700	[thread overview]
Message-ID: <20200423004807.GC161058@localhost> (raw)
In-Reply-To: <CAJfpegt=xe-8AayW2i3AYrk3q-=Pp_A+Hctsk+=sXoMed5hFQA@mail.gmail.com>

On Wed, Apr 22, 2020 at 09:55:56AM +0200, Miklos Szeredi wrote:
> On Wed, Apr 22, 2020 at 8:06 AM Michael Kerrisk (man-pages)
> <[email protected]> wrote:
> >
> > [CC += linux-api]
> >
> > On Wed, 22 Apr 2020 at 07:20, Josh Triplett <[email protected]> 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.
> 
> If this is primarily an io_uring feature, then why burden the normal
> openat2 API with this?

This feature was inspired by io_uring; it isn't exclusively of value
with io_uring. (And io_uring doesn't normally change the semantics of
syscalls.)

> This would also allow Implementing a private fd table for io_uring.
> I.e. add a flag interpreted by file ops (IORING_PRIVATE_FD), including
> openat2 and freely use the private fd space without having to worry
> about interactions with other parts of the system.

I definitely don't want to add a special kind of file descriptor that
doesn't work in normal syscalls taking file descriptors. A file
descriptor allocated via O_SPECIFIC_FD is an entirely normal file
descriptor, and works anywhere a file descriptor normally works.

  reply	other threads:[~2020-04-23  0:48 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-22  5:19 [PATCH v5 0/3] Support userspace-selected fds Josh Triplett
2020-04-22  5:19 ` [PATCH v5 1/3] fs: Support setting a minimum fd for "lowest available fd" allocation Josh Triplett
2020-04-22  6:06   ` Michael Kerrisk (man-pages)
2020-04-23  1:12   ` Dmitry V. Levin
2020-04-23  4:51     ` Josh Triplett
2020-04-23  9:24   ` Arnd Bergmann
2020-04-22  5:20 ` [PATCH v5 2/3] fs: openat2: Extend open_how to allow userspace-selected fds Josh Triplett
2020-04-22  6:06   ` Michael Kerrisk (man-pages)
2020-04-22  7:55     ` Miklos Szeredi
2020-04-23  0:48       ` Josh Triplett [this message]
2020-04-23  4:24         ` Miklos Szeredi
2020-04-23  4:42           ` Josh Triplett
2020-04-23  6:04             ` Miklos Szeredi
2020-04-23  7:33               ` Josh Triplett
2020-04-23  7:45                 ` Miklos Szeredi
2020-04-23  7:57                   ` Miklos Szeredi
2020-04-23  9:20                     ` Miklos Szeredi
2020-04-23  9:46                       ` Miklos Szeredi
2020-04-23  8:06                   ` Josh Triplett
2020-04-22  5:20 ` [PATCH v5 3/3] fs: pipe2: Support O_SPECIFIC_FD Josh Triplett
2020-04-22  6:06   ` Michael Kerrisk (man-pages)
2020-04-22 15:44   ` Florian Weimer
2020-04-23  0:44     ` Josh Triplett
2020-04-22  6:05 ` [PATCH v5 0/3] Support userspace-selected fds Michael Kerrisk (man-pages)

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