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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 23 Aug 2017 19:01:10 -0700
Message-ID: <CA+55aFwvwtFCH2THn1LirOpMsZ57pnNi61nXQfQ6NBgakdXpTQ@mail.gmail.com>
Subject: Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Stefan Lippers-Hollmann <s.l-h@gmx.de>,
        Christian Brauner <christian.brauner@canonical.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Thorsten Leemhuis <regressions@leemhuis.info>
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On Wed, Aug 23, 2017 at 6:49 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Argh. And it's *not* fairly straightforward, because the
> tty_operations "ioctl()" function pointer only gets 'struct tty *'.
>
> So in the TIOCGPTPEER path, we don't actually have access to the file
> pointer of the fd we're doing the ioctl on.
>
> And that's where the 'struct path' to the 'ptmx' node is - which we
> need to then look up the 'pts' directory.
>
> How very annoying. I think that's why we did it all at ptmx_open()
> time, because then we had all the information.

Anyway, the revert is pushed out. So we're back to the old behavior
that gives the wrong pathname in /proc.

And I think I can handle the lack of a 'struct file *' to the ioctl
operations by just special-casing TIOCGPTPEER directly in tty_ioctl()
itself.

That's where we handle "generic" tty ioctls, and doing pty stuff there
is kind of wrong, but pty's are special.

But I think I'll leave it for tomorrow. So Eric, if you feel like
looking at this, I'd appreciate it.

                Linus