linux-kernel - Re: [PATCH v5 2/3] fs: openat2: Extend open

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Message-ID: <CAJfpegtXj4bSbhpx+=z=R0_ZT8uPEJAAev0O+DVg3AX242e=-g@mail.gmail.com>
Date:   Thu, 23 Apr 2020 09:45:45 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Josh Triplett <josh@...htriplett.org>
Cc:     Michael Kerrisk <mtk.manpages@...il.com>, io-uring@...r.kernel.org,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>, Jens Axboe <axboe@...nel.dk>,
        Aleksa Sarai <cyphar@...har.com>,
        linux-man <linux-man@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v5 2/3] fs: openat2: Extend open_how to allow
 userspace-selected fds

On Thu, Apr 23, 2020 at 9:33 AM Josh Triplett <josh@...htriplett.org> wrote:

> > What are the plans for those syscalls that don't easily lend
> > themselves to this modification (such as accept(2))?
>
> accept4 has a flags argument with more flags available, so it'd be
> entirely possible to cleanly extend it further without introducing a new
> version.

Variable argument syscalls, you are thinking?

> > I mean, you could open the file descriptor outside of io_uring in such
> > cases, no?
>
> 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...

Thanks,
Miklos