/etc/mtab vs. /proc/mounts

[Alan Bateman]

I think I need help to (re)understand the difference between /etc/mtab 
and /proc/mounts on Linux.

On Linux, our getFileStores() is implemented to essentially enumerate 
/etc/mtab. That should give a similar list to what df(1) prints although 
the filtering may be slightly different. On the other hand the 
getFileStore method to get the FileStore for where a file is located 
uses /proc/mounts to find the mount point (folks on this list may recall 
the reasons why we switched to using /proc [1]).  Using both leads to at 
least one reported anomaly where it has been observed that getFileStore 
returns a FileStore representing the root file system with both a name 
and type of rootfs but df -T (and getFileStores) report something 
different (/dev/sda1 and ext4 on one system I tried). I'm trying to 
figure if this code should be changed and what the right answer is for 
this case. Any suggestions?

Thanks,

-Alan

[1] http://mail.openjdk.java.net/pipermail/nio-dev/2009-May/000545.html