>I added a mount option in my kernel (MNT_GETARGS), that retrieves the
>fs-specific mount arguments. The code is pretty straight forward and
>allows one to do:

Sounds interesting.  I thought for a bit that it might allow fixing 
PR#698 but that really wants additional info stored in the kernel.
This is so that umount could know that fs while an NFS mount to the kernel
is actually something else (eg sNFS) and to look for umount_snfs rather
than simply send an NFS MOUNTPROC_UMNT rpc to the supposed server 
when the kernel is really talking to a local process. 

--sjg