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

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Date:	Tue, 21 Feb 2012 19:47:38 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>, Ian Kent <raven@...maw.net>
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com,
	autofs@...ux.kernel.org, thomas@...3r.de, viro@...iv.linux.org.uk
Subject: Re: compat: autofs v5 packet size ambiguity - update

On Tue, Feb 21, 2012 at 7:33 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> But I'm sure that the autofs daemon does something simple that we can
> depend on in practice.

I didn't find the most recent source code, but the first thing that
automount.c does after calling "mount" (which is a for+exec, so we
cannot take the mounting is_compat_task() into account is to open the
new root for the ioctlfd, and then it does a stat.

And then it does a AUTOFS_IOC_PROTOVER ioctl to see what the protocol
version is.

So we could just decide that

 (a) we add a mount option for the packet size (or just "v6" - which
would be "v5 with a fixed packet size")

 (b) in the absence of an explicit mount option, we look at
is_compat_task() for the first AUTOFS_IOC_PROTOVER ioctl we get.

That looks fairly straightforward and safe. Hmm?

Where are the automount sources supposed to be, anyway? kernel.org has
a v5 directory, but it's empty.

                Linus
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