linux-kernel - Re: [PATCH 00/17] [RFC] AFS: Implement OpenAFS pioctls(version)s

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Message-ID: <20090617183745.GI8633@ZenIV.linux.org.uk>
Date:	Wed, 17 Jun 2009 19:37:45 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andreas Dilger <adilger@....com>,
	David Howells <dhowells@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, akpm@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-afs@...ts.infradead.org
Subject: Re: [PATCH 00/17] [RFC] AFS: Implement OpenAFS pioctls(version)s

On Wed, Jun 17, 2009 at 09:09:47AM -0700, Linus Torvalds wrote:
> We've traditionally had that magic "open with flag=3" to do a magic open 
> of device files without waiting, and we have O_NOFOLLOW to open symlinks 
> without following them (sadly, it just errors out, rather than opening the 
> symlink, but that's another detail). 
> 
> So I think it should be solvable some way, but not by trying to find the 
> mount point.

O_NOFOLLOW *will* open their mountpoints just fine, without triggering
automount.  Of course, if something's already mounted there, it will
get you the covering object.  Which is a feature, as far as I'm concerned,
since "I've overmounted that to have it unreachable" shouldn't be breakable
regardless of the syscall we are using - be it open() or pioctl().

FWIW, count me strongly opposed to that shit; it's too damn ugly to live,
has interesting security implications and we'll get stuck with it forever.
And we *really* don't need another multiplexor from hell, without anything
resembling well-defined semantics.
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