linux-kernel - Re: [RFC] fix devpts mount behavior

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Message-ID: <CAPXgP12hk4iQNYGVrcKG1xBEJ2TmCH8jDx-E+1a8Mw8wiWCeDA@mail.gmail.com>
Date:	Sat, 28 Jan 2012 22:32:06 +0100
From:	Kay Sievers <kay.sievers@...y.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Serge Hallyn <serge.hallyn@...onical.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	containers@...ts.linux-foundation.org,
	Dave Hansen <haveblue@...ibm.com>,
	linux-kernel@...r.kernel.org, Andy Whitcroft <apw@...onical.com>,
	sukadev@...ux.vnet.ibm.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC] fix devpts mount behavior

On Sat, Jan 28, 2012 at 21:52, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> Serge Hallyn <serge.hallyn@...onical.com> writes:
>
>> Quoting Kay Sievers (kay.sievers@...y.org):
>>> We might also thing about changing /sys/class/tty/ptmx/, and have the
>>> kernel create the symlink? The loops through userspace to setup
>>> default kernel stuff are kind of crazy ...

>> sorry, there is something I'm missing here.  Without a target kobj
>> to link to, how would we go about telling the kernel that /dev/ptmx
>> should be a symlink to /dev/pts/ptmx?  Is there a way to do that?

There is no support for symlinks in the core at the moment. But I
guess we could just add support for it to the driver core and devtmpfs
to create a symlink in /dev instead of a device node.

The ptmx device would need to pass that information along to the
driver core call when creating the ptmx device.

> There is precedent in the /dev/fd symlinks, so I expect you want
> to look and see where the configuration for that comes from.

That's a static list of stuff created at startup. But it's easier to
do in usersace, because /proc is not configurable or optional for
usual use cases, so we can just do it unconditionally in userspace.
They also can not conflict with device nodes.

Kay
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