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Subject: Re: compat: autofs v5 packet size ambiguity - update
From: Ian Kent <raven@themaw.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Miller <davem@davemloft.net>, linux-kernel@vger.kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, autofs@vger.kernel.org,
        Thomas Meyer <thomas@m3y3r.de>, Al Viro <viro@zeniv.linux.org.uk>
Date: Thu, 23 Feb 2012 10:09:15 +0800
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On Wed, 2012-02-22 at 17:56 -0800, Linus Torvalds wrote:
> On Wed, Feb 22, 2012 at 5:48 PM, Ian Kent <raven@themaw.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