Hi All,

Based on comments from Hugh & Andrea, I took a shot at implementing
madvise(MADV_TRUNCATE) - which truncates range of pages in the file.
(basically provides ability to punche a hole in to the file).

Basically, I added "truncate_range" inode operation to provide
opportunity for the filesystem to zero the blocks and/or free
them up. 

I also attempted to implement shmem_truncate_range() which 
needs lots of testing before I work out bugs :(

I would really appreciate your comments on my approach.

Thanks,
Badari