From: Linus Torvalds <torvalds@linux-foundation.org>
To: Christian Brauner <christian.brauner@canonical.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Serge Hallyn <serge@hallyn.com>,
Stefan Lippers-Hollmann <s.l-h@gmx.de>,
Christian Brauner <christian.brauner@ubuntu.com>,
Thorsten Leemhuis <regressions@leemhuis.info>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name
Date: Thu, 24 Aug 2017 12:22:19 -0700 [thread overview]
Message-ID: <CA+55aFwKth0Dy+KgWdo3zaq4ur3_Sj5hgAPrvcZLo1BaQwZk=w@mail.gmail.com> (raw)
In-Reply-To: <CAPP7u0WHqDfxTW6hmc=DsmHuoALZcrWdU-Odu=FfoTX26SGHQg@mail.gmail.com>
On Thu, Aug 24, 2017 at 12:01 PM, Christian Brauner
<christian.brauner@canonical.com> wrote:
>
> I've touched on this in my original message, I wonder whether we currently
> support mounting devpts at a different a location and expect an open on a
> newly created slave to work.
Yes. That is very much intended to work.
> Say I mount devpts at /mnt and to open("/mnt/ptmx", O_RDWR | O_NOCTTY) and get a new slave pty at /mnt/1 do we
> expect open("/mnt/1, O_RDWR | O_NOCTTY) to work?
Yes.
Except you actually don't want to use "/mnt/ptmx". That ptmx node
inside the pts filesystem is garbage that we never actually used,
because the permissions aren't sane. It should probably be removed,
but because somebody *might* have used it, we have left it alone.
So what you're actually *supposed* to do is
- create a ptmx node and a pts directory in /mnt
- mount devpts on /mnt/pts
- use /mnt/ptmx to create new pty's, which should just look up that
pts mount directly.
And yes, the pathname should then be /mnt/pts/X for the slave side,
and /mnt/ptmx for the master.
In fact, I just tested that TIOCGPTPEER, including using your original
test-program (this is me as root in my home directory):
[root@i7 torvalds]# mkdir dummy
[root@i7 torvalds]# cd dummy/
[root@i7 dummy]# mknod ptmx c 5 2
[root@i7 dummy]# mkdir pts
[root@i7 dummy]# mount -t devpts devpts pts
[root@i7 dummy]# ../a.out
I point to "/home/torvalds/dummy/pts/0"
[root@i7 dummy]# umount pts/
[root@i7 dummy]# cd ..
[root@i7 torvalds]# rm -rf dummy
There's two things to note there:
- look at that "I point to" - it's not hardcoded to /dev/pts/X
- look at the pts number: each pts filesystem has its own private
numbers, so despite the fact that in another window I *also* have that
ptx/0:
[torvalds@i7 linux]$ tty
/dev/pts/0
that new devpts instance has its *own* pts/0, which is a
completely different pty.
this is one of those big cleanups we did with the pts filesystem some time ago.
Linus
next prev parent reply other threads:[~2017-08-24 19:22 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-16 17:12 [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Christian Brauner
2017-08-16 17:12 ` [PATCH 1/1] " Christian Brauner
2017-08-16 18:26 ` [PATCH 0/1] " Linus Torvalds
2017-08-16 18:48 ` Linus Torvalds
2017-08-16 19:48 ` Christian Brauner
2017-08-16 19:56 ` Linus Torvalds
2017-08-16 20:19 ` Linus Torvalds
2017-08-16 20:30 ` Linus Torvalds
2017-08-16 21:03 ` Linus Torvalds
2017-08-16 21:37 ` Christian Brauner
2017-08-16 21:45 ` Linus Torvalds
2017-08-16 21:55 ` Linus Torvalds
2017-08-16 22:05 ` Christian Brauner
2017-08-16 22:28 ` Christian Brauner
2017-08-23 15:31 ` Eric W. Biederman
2017-08-23 21:15 ` Christian Brauner
2017-08-16 22:46 ` Eric W. Biederman
2017-08-16 22:58 ` Linus Torvalds
2017-08-16 23:51 ` Eric W. Biederman
2017-08-17 0:08 ` Linus Torvalds
2017-08-17 1:24 ` Eric W. Biederman
2017-08-24 0:24 ` Stefan Lippers-Hollmann
2017-08-24 0:42 ` Linus Torvalds
2017-08-24 1:16 ` Linus Torvalds
2017-08-24 1:25 ` Eric W. Biederman
2017-08-24 1:32 ` Linus Torvalds
2017-08-24 1:49 ` Linus Torvalds
2017-08-24 2:01 ` Linus Torvalds
2017-08-24 3:11 ` Eric W. Biederman
2017-08-24 3:24 ` Linus Torvalds
2017-08-24 15:51 ` Eric W. Biederman
2017-08-24 4:24 ` Stefan Lippers-Hollmann
2017-08-24 15:54 ` Eric W. Biederman
2017-08-24 17:52 ` Linus Torvalds
2017-08-24 18:06 ` Linus Torvalds
2017-08-24 18:13 ` Linus Torvalds
2017-08-24 18:31 ` Linus Torvalds
2017-08-24 18:36 ` Linus Torvalds
2017-08-24 20:24 ` Stefan Lippers-Hollmann
2017-08-24 20:27 ` Linus Torvalds
2017-08-24 18:40 ` Eric W. Biederman
2017-08-24 18:51 ` Linus Torvalds
2017-08-24 19:23 ` Eric W. Biederman
2017-08-24 20:13 ` [PATCH v3] pty: Repair TIOCGPTPEER Eric W. Biederman
2017-08-24 21:01 ` Stefan Lippers-Hollmann
[not found] ` <CAPP7u0WHqDfxTW6hmc=DsmHuoALZcrWdU-Odu=FfoTX26SGHQg@mail.gmail.com>
2017-08-24 19:22 ` Linus Torvalds [this message]
2017-08-24 19:25 ` [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds
2017-08-24 20:43 ` Eric W. Biederman
2017-08-24 21:07 ` Linus Torvalds
2017-08-24 23:01 ` Eric W. Biederman
2017-08-24 23:27 ` Linus Torvalds
2017-08-24 23:37 ` Christian Brauner
2017-08-26 1:00 ` Linus Torvalds
2017-08-24 19:48 ` Eric W. Biederman
2017-08-17 1:37 ` Eric W. Biederman
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