From mboxrd@z Thu Jan  1 00:00:00 1970
From: hooanon05@yahoo.co.jp
Subject: Re: Fallthrus as full-length symlinks?
Date: Wed, 25 Nov 2009 11:36:03 +0900
Message-ID: <32549.1259116563@jrobl>
References: <20091113174631.GD19656@shell> <30797.1258523235@jrobl> <20091125021509.GF21724@shell>
Cc: linux-fsdevel@vger.kernel.org,
	David Woodhouse <dwmw2@infradead.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Jan Blunck <jblunck@suse.de>,
	Christoph Hellwig <hch@infradead.org>,
	Andy Whitcroft <apw@canonical.com>,
	Scott James Remnant <scott@canonical.com>,
	Sandu Popa Marius <sandupopamarius@gmail.com>,
	Jan Rekorajski <baggins@sith.mimuw.edu.pl>,
	Arnd Bergmann <arnd@arndb.de>,
	Vladimir Dronnikov <dronnikov@gmail.com>,
	Felix Fietkau <nbd@openwrt.org>
To: Valerie Aurora <vaurora@redhat.com>
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Valerie Aurora:
> On Wed, Nov 18, 2009 at 02:47:15PM +0900, hooanon05@yahoo.co.jp wrote:
	:::
> > I think the idea of fallthru entry is good, even if it is implemented as
> > a special symlink.
> > How do you think about the file paths in /proc/pid/maps and
> > /proc/pid/fd?
> > They refer the file paths, and some apps depend upon these path. I
> > remember that the package manager in debian didn't work when the path is
> > wrong. (But I don't know whether it is true still).
> > 
> > Will FS have to support such case?
> 
> My current thinking is that an overlay shouldn't be mounted over /proc
> or other special file systems.  I think that a writable layer should
> only be mounted over exactly one file system, no submounts allowed.

No, that is not what I mean.
When a fallthru entry is implemented as a kind of a symlink, what will
they look like via /proc/pid/{fd,maps,cwd,exe}?

For example,
$ ln -s /bin/sleep /tmp/awake
$ /tmp/awake 100 &
[1] 32524
$ ls -l /proc/32524/exe
lrwxrwxrwx 1 jro jro 0 Nov 25 11:25 exe -> /bin/sleep*

It shows the target path (real filename) even if I execute it as a
symlink name.

When I invoke /UnionMount/fallthru/a.out, and if /proc/pid/exe
shows something like /real/filesystem/a.out, then some app (debian
start-stop-deamon(8) or something) may not work, I am afraid.

Sorry if my poor English made you misunderstood. But I hope I could make
my question clear now.


J. R. Okajima