How to determine a path is a mountpoint.

[Stef Bon <stef@bononline.nl>]

Hello,

I'm working on a construction of the automounter in combination with a fuse 
module.
The automounter is the mounthelper.
I'm looking for a way to determine in C a directory is a mountpoint, specially
a autofs managed directory, so a virtual directory created by the automounter.

I can parse the /etc/mtab file or /proc/mounts, like in bash:

cat /proc/mounts | grep --word-regexp "$mountpoint"

but this is slow.. I have looked to the code of the program mountpoint,
but this is not possible in an autofs maneged directory. This program
does a cd to the directory and checks the filesystem changes. With autofs this 
makes the mountpoint always mounted, which is of course not what I'm looking 
for.

Stef