linux-kernel - Re: [PATCH] Fix __d_path for lazy unmounts

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Message-Id: <E1Nm2V2-0006d5-Ri@pomaz-ex.szeredi.hu>
Date:	Mon, 01 Mar 2010 11:05:16 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	John Johansen <john.johansen@...onical.com>
CC:	miklos@...redi.hu, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] Fix __d_path for lazy unmounts

On Fri, 26 Feb 2010, John Johansen wrote:
> On 02/26/2010 04:07 AM, Miklos Szeredi wrote:
> > On Sat, 20 Feb 2010, john.johansen@...onical.co wrote:
> >> From: John Johansen<john.johansen@...onical.com>
> >>
> >> When __d_path() hits a lazily unmounted mount point, it tries to prepend
> >> the name of the lazily unmounted dentry to the path name.  It gets this wrong,
> >> and also overwrites the slash that separates the name from the following
> >> pathname component. This patch fixes that; if a process was in directory
> >> /foo/bar and /foo got lazily unmounted, the old result was ``foobar'' (note the
> >> missing slash), while the new result with this patch is ``/foo/bar''.
> >
> > Example:
> >
> > # mkdir -p /tmp/foo/bar
> > # mkdir /tmp/mnt
> > # mount --bind /tmp/foo /tmp/mnt
> > # cd /tmp/mnt/bar
> > # /bin/pwd
> > /tmp/mnt/bar
> > # umount -l /tmp/mnt
> > # /bin/pwd
> > foobar
> >
> > After the patch it will be /foo/bar.
> >
> > Why is the path starting with "/foo"?  Does that make any sense?
> >
> not a lot except, connecting disconnected paths to root is what
> is currently done for paths that aren't reachable but have an fs
> as their root (ie the last dentry is / so it looks connected to
> root).

/tmp (which contains /foo/bar) is not a root of anything.  So even
that logic doesn't hold for your current patch.

/tmp/foo *was* the root of the mount, so "/bar" would make a tiny
little more sense.  But "/bar" looks like a normal connected patch,
which it is not, so it's not really a good solution either.

Thanks,
Miklos
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