Alright sir. I will send you queries on Email. :)
At present I am able to read files having extents based files.
But I need to call bmap routine for extents based files explicitly. I want to invoke it automatically according the value of field i_flags in inode. I see i_flag value should be different for files supporting extents from the files which dont support. but It is same in my case.
another generic problem that will help me considerably is I want to disable/clear cache memory. I want corresponding to each command in userland, there is lower level disk read. Which will help me in tracing fs routines.