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

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Message-ID: <20120124002555.GA29534@sergelap>
Date:	Mon, 23 Jan 2012 18:25:55 -0600
From:	Serge Hallyn <serge.hallyn@...onical.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Hansen <haveblue@...ibm.com>, sukadev@...ux.vnet.ibm.com,
	Andy Whitcroft <apw@...onical.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Matt Helsley <matthltc@...ibm.com>,
	linux-kernel@...r.kernel.org, containers@...ts.linux-foundation.org
Subject: Re: [RFC] fix devpts mount behavior

Quoting Linus Torvalds (torvalds@...ux-foundation.org):
> On Mon, Jan 23, 2012 at 4:05 PM, Serge Hallyn
> <serge.hallyn@...onical.com> wrote:
> >
> > I've been playing for the last week with ways to fix this, and in the
> > end I can see two ways.
> 
> How about a third way:
> 
>  - make "newinstance" mandatory (and "-o newinstance" is a no-op) and
> forget about the whole issue.
> 
>  - if you really want to remount the old global one, you have to use a
> bind mount of that original mount instead.
> 
> There may be some subtle reason why the above is totally broken and
> just fundamnetally wouldn't work, and breaks all existing setups, but
> maybe it's worth at least discussing as an option?
> 
> Or did I entirely misunderstand the problem?
> 
>                       Linus

I like it.

The only place that *might* be a problem is if initramsfs does a devpts
mount, and later init blindly mounts tmpfs on /dev and mounts a new
devpts.  But it seems unlikely there would be any open pty's so it
shouldn't really matter.

I could go ahead and test that, say, ubuntu and fedora systems boot fine
with this change.  But of course I can't be sure there is no userspace
out there that won't cope...

-serge
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