Re: Symlink indirection

From: Andrew Walrond (
Date: Sat Dec 14 2002 - 07:47:21 EST

Joseph Fannin wrote:
> I don't understand what you are trying to explain. Do you mean a
> union mount, or a variation thereof?
> I thought Al Viro was going to do union mount support for 2.5, but
> I haven't heard about it in a while. Maybe it went in and no one noticed?

Hi Joseph

I'm not familiar with the phrase 'union mount' and although google gives
wads of hits, I can't find a good description of it

What I mean is (contrived example with made-up mount option --overlay)

mkdir a
echo "a/x" > a/x
echo "a/y" > a/y
echo "a/z" > a/z

mkdir b
echo "b/y" > b/y

mkdir c
echo "c/z" > c/z

mkdir d
mount --bind a d
mount --bind --overlay b d
mount --bind --overlay c d

cat d/x

cat d/y

cat d/z

This would be *really* useful and nice. I currently emulate this
behavior with a bash script which creates hard or soft links, but the
mounting system would be much nicer, easier to unwind etc.

I assume this isn't possible now (man mount gives no hint), but how
feasible is it? Has anybody tried to implement this? If yes and No
perhaps I could (with some initial guidance) have a look at implementing

I don't use HD's much anymore, so it would need to work for tmpfs.

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