Replicating directories - Intercepting write/modify system calls

["Siddhartha Jain" <sid@netmagicsolutions.com>]

Hello,

I need a module/tool to replicate directories locally or across a network.
Locally, the master and the mirror directories may not belong to the same
FS. My immiediate need is to replicate a NFS-mounted directory to another
local/NFS directory. So here is what I figured:

1. A config file contains the master and mirror paths
2. Expand the vnode structure to include two things: a bit-flag to indicate
that the vnode has a replica and a pointer to the replica vnode.
3. When an open() is called,
	a. check if the read/modify option is set in the open() (I am not
interested in replicating access-time at the moment).
	b. If yes, check the path of the file against the known masters in the
config.
	c. If it matches, copy the file to a destination specified by the mirror's
path.
	d. Set the flag in the master vnode for replica and place a pointer to the
replica vnode in the master's structure.
	e. After this replicate all write() calls for the master vnode to the
replica vnode.
	f. close() the replica vnode when the master is close()-ed.


Being a sysadmin and not really a C/Kernel programmer, I do not know how
much is this feasible and practical.

Given that it is ok, how do I avoid the copy at open() and do only
incremental changes everytime a file is closed and re-opened.

Regards,

Siddhartha