Adding snapshot capability to Linux

["Libor Vaněk" <libor@conet.cz>]

Hi,
I'm going to start my dissertation work which is "Adding snapshop 
capability to Linux kernel with copy-on-write support". My idea is add 
it as another VFS - I know that there is some snapshot support in LVM 
but it's working on "device-level" and I'd like/have to do it on fs level.

My idea is to use it this way:
- I have running system with some "/foo" dir
- I want to make snapshot of "/foo/bar" to "/foo/snap1"
- I run "mount -t snapshot /foo/bar /foo/snap1"
- This creates virtual image of "/foo/bar" to the "/foo/snap1" with 
hidden file (something like journal) in "/foo/snap1" - all files are 
linked to "/foo/bar"
- Whenever is some file/dir changed in "/foo/bar" there is created 
physical copy of it to the snapshot(s) before writing changes (for 
making records about this will be used the hidden file)
- Of course that one directory can be snapshoted more times
- Probably the hidden file with records about all snapshots and details 
should be stored in "/foo/bar"
- Question is how to handle ACLs and EA for XFS/JFS/... and if it won't 
collide with journal

I'd like to do it not only because I have to but I want people to use it 
(I want to make it GPL) and maybe it will be one nice day part of Linux 
kernel ;-)

So I'd like if you can send me any suggestions/tips/warnings/links etc. 
before I start coding so I know what should I avoid/use.

Thanks,
Libor