should df looked at /proc/mounts on linux?

[Marty Leisner]

I had a "head-scratching" incident when dealing with applications
which called umount(2) and then trying to run df to see what is done.
/proc/mounts is the kernels idea of what's mounted, /etc/mtab is manipulted
in user space.

df uses calls with look at /etc/mtab.

I've heard of a technique to link /etc/mtab to /proc/mounts, which 
seems like a good idea (I've never seen a distribution which does this).

When /etc/mtab is out of sync with /proc/mounts, strange things start
happening  regarding user space information 
(doing df was obviously wrong, so was mount(1).

Should df start by seeing if /proc/mounts exists, and then 
using it if it does (falling back onto /etc/mtab?)

marty