linux-kernel - Re: [PATCH] vfs: automount should ignore LOOKUP

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Date:	Tue, 06 Sep 2011 17:39:53 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Ian Kent <raven@...maw.net>
Cc:	David Howells <dhowells@...hat.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Leonardo Chiquitto <leonardo.lists@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	autofs@...ux.kernel.org
Subject: Re: [PATCH] vfs: automount should ignore LOOKUP_FOLLOW

Ian Kent <raven@...maw.net> writes:

> On Tue, 2011-09-06 at 10:09 +0200, Miklos Szeredi wrote:
>> Ian Kent <raven@...maw.net> writes:
>> 
>> > On Mon, 2011-09-05 at 19:02 +0200, Miklos Szeredi wrote:
>> >> 
>> >> If automounting on lstat(2) is the correct behavior (is it?  why?)  then at
>> >> least it should be enabled by a global switch or mount option, IMO.
>> >
>> > Ideally we wouldn't need to take special precautions for these
>> > operations at all but we can't, especially for GUI environments that
>> > constantly scan file systems on mount/umount activity.
>> >
>> > Historically for autofs, neither stat(2) or lstat(2) would trigger a
>> > mount. With the current implementation stat(2) now does but lstat(2)
>> > doesn't which is a step in the right direction IMHO. So, I recommend we
>> > continue to encourage user space to make the needed changes so we
>> > continue to move in the right direction, and yes, I acknowledge it is a
>> > pain but it'll never get done otherwise.
>> 
>> I'm not quite convinced.  What's the advantage of triggering automount
>> on stat(2)?
>
> You get the information of the directory of the mounted fs and for many
> peoples purposes automounting should be transparent so that would be
> best.

The same is true for lstat(2).

>  
>> 
>> Has anybody complained that stat(2) on the mountpoint doesn't cause an
>> automount?
>
> Yes, based on the reasoning above.

Would any of those complaints go away if stat(2) did cause an
automount and lstat(2) didn't?

With AT_NO_AUTOMOUNT I can agree with, that's a flag specifically about
not automounting.  Unlike AT_SYMLINK_NOFOLLOW which is about following
symlinks and hasn't got a lot to do with automounts.

Thanks,
Miklos
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