Re: Symlink indirection

[Andrew Walrond <andrew@walrond.org>]

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
"a/x"

cat d/y
"b/x"

cat d/z
"c/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 
this.

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