Re: Direct VFS/SB Access and Private Submounting

[Christopher Allen Wing <wingc@engin.umich.edu>]

Hello,

not sure if someone has written you back about this already, but what you 
are trying to do (look 'underneath' a mount point) can be done easily 
without kernel modifications.

You can bind mount an existing filesystem to a new location, and examine 
its contents without following existing mount points.

e.g. suppose you want to look at the directory on your root filesystem 
upon which /proc is mounted:

 	# mount |grep 'on /proc type proc'
 	none on /proc type proc (rw)

this is what the root of the /proc filesystem looks like:

 	# ls -ld /proc
 	dr-xr-xr-x  200 root root 0 Mar  1 18:06 /proc


Now, temporarily bind mount the root to someplace else:

 	# mkdir /tmp/look
 	# mount --bind / /tmp/look


Now you can examine the directory underlying /proc in the root:

 	# ls -ld /tmp/look/proc
 	drwxr-xr-x  2 root root 4096 Sep 26  2005 /tmp/look/proc

 	# umount /tmp/look



In general I would assume that a package manager shouldn't be concerned 
about these types of things, since permanent mountpoints should always be 
mounted when a system is in its normal state, thus there would be no 
reason to care about what's 'underneath' a mountpoint.  (If someone had 
root access, they could be hiding stuff there, but it they had root access 
they could do a whole lot of other bad things)


-Chris Wing
wingc@engin.umich.edu