linux-kernel - Re: compat: autofs v5 packet size ambiguity

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Message-ID: <1329962955.2244.16.camel@perseus.themaw.net>
Date:	Thu, 23 Feb 2012 10:09:15 +0800
From:	Ian Kent <raven@...maw.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>, autofs@...r.kernel.org,
	Thomas Meyer <thomas@...3r.de>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: compat: autofs v5 packet size ambiguity - update

On Wed, 2012-02-22 at 17:56 -0800, Linus Torvalds wrote:
> On Wed, Feb 22, 2012 at 5:48 PM, Ian Kent <raven@...maw.net> wrote:
> >
> > Sorry, I think your wrong this time.
> 
> Well, that would be good, actually. Doing the test itself at mount
> time is certainly the simpler approach.
> 
> >> The autofs "mount" is done by fork + execve("mount").
> >
> > It's done like this when mounting things inside an already mounted
> > indirect autofs mount or when mounting things on autofs direct mount
> > triggers but, in version 5, mount(2) has always used to mount autofs
> > file systems.
> 
> Is that true for legacy autofs daemons too that distros ship? Because
> those are the ones we'd be fighting..

That's a good point.

> 
> Because when I do
> 
>     git grep '\<mount[  ]*(' -- '*.[ch]'
> 
> (that's a space and a tab in that pattern) on the autofs-4.1.4 sources
> I downloaded, I don't see a single call to mount. But I do see
> spawning of PATH_MOUNT. And one of them is with "-t", "autofs".

Sure, that's true, and you'll see it uses the mount option maxproto with
the value of AUTOFS_MAX_PROTO_VERSION. But autofs uses it's own copy of
the headers so AUTOFS_MAX_PROTO_VERSION is 4 not 5 so it won't be
affected by this change.

Ian

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