Disk Quota for user and group ???
 

Hi
I have a problem in linux disk quota.
Say there is a system user 'usr1' with initial group 'usr1'. On a particular file system, there may exists files

File1. -> User = usr1 group = usr1
File2. -> User = usr2 group = usr1
Fiel3. -> User = usr1 group = grp1

user of file2 and group of file3 can't be changed.
Now is it possible to set disk quota on that file system in such a way that the total size of all the files, owned by either user 'usr1' or group 'usr1', should not exceed to a particular limit (say 100MB).
I have tried to solve it in number of ways but can't get the solution.

Any Idea?
Thanks in Advance
Sultan