From: Miklos Szeredi <miklos@szeredi.hu>
To: Josh Triplett <josh@joshtriplett.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>,
io-uring@vger.kernel.org,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Arnd Bergmann <arnd@arndb.de>, Jens Axboe <axboe@kernel.dk>,
Aleksa Sarai <cyphar@cyphar.com>,
linux-man <linux-man@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH v5 2/3] fs: openat2: Extend open_how to allow userspace-selected fds
Date: Thu, 23 Apr 2020 11:20:44 +0200 [thread overview]
Message-ID: <CAJfpegvcW9Sic8ZXgWfFQ3d8JTr53XABfP8rZzsVhCDBKCgMBw@mail.gmail.com> (raw)
In-Reply-To: <CAJfpegtgrUACZpYR8wWoTE=Hh4Xi+4rRfrZTxRtaFVpT9GMPjw@mail.gmail.com>
On Thu, Apr 23, 2020 at 9:57 AM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> On Thu, Apr 23, 2020 at 9:45 AM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> > > I would prefer to not introduce that limitation in the first place, and
> > > instead open normal file descriptors.
> > >
> > > > The point of O_SPECIFIC_FD is to be able to perform short
> > > > sequences of open/dosomething/close without having to block and having
> > > > to issue separate syscalls.
> > >
> > > "close" is not a required component. It's entirely possible to use
> > > io_uring to open a file descriptor, do various things with it, and then
> > > leave it open for subsequent usage via either other io_uring chains or
> > > standalone syscalls.
> >
> > If this use case arraises, we could add an op to dup/move a private
> > descriptor to a public one. io_uring can return values, right?
> >
> > Still not convinced...
>
> Oh, and we haven't even touched on the biggest advantage of a private
> fd table: not having to dirty a cacheline on fdget/fdput due to the
> possibility of concurrent close() in a MT application.
>
> I believe this is a sticking point in some big enterprise apps and it
> may even be a driving force for io_uring.
https://lwn.net/Articles/787473/
And an interesting (very old) article referenced from above, that
gives yet a new angle on fd allocation issues:
https://lwn.net/Articles/236843/
A private fd space would be perfect for libraries such as glibc.
Thanks,
Miklos
next prev parent reply other threads:[~2020-04-23 9:21 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
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 [this message]
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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