ecryptfs.mount_private should not try to update mtab if it is a symlink

Bug Description

ecryptfs.mount_private currently attempts to update mtab even if it is a symbolic link. When mtab is symlinked to /proc/mounts, there is no point updating it and even worse, it will fail (see https://bugzilla.redhat.com/show_bug.cgi?id=706911).

Please find attached a patch that addresses the issue and that I tested successfully on my Machine (running Fedora 15). Without the patch, ecryptfs-mount-private fails with a "addmntent: Invalid argument" error.

Any comment on this?

Please note that other programs such as mount.cifs have experienced the exact same issue and they have fixed it the same way [1].

[1] http://git.samba.org/rsync.git/?p=cifs-utils.git;a=commitdiff_plain;h=fba28cfe2f13dd8bdae3cec76178f42b001a40ca

Thanks, Christophe. This looks good to me.

This was fixed a while ago in ecryptfs-utils-89, but not closed. Sorry! See revision 539.1.1.