Recent FreeBSD, NFSv4 and /var/db/mounttab

Hi,

Last month, I started switching all my systems (stable/9, stable/10, 
stable/11 and current) to NFSv4, and I found that:

   on current (svn 312652) an entry is added to /var/db/mounttab by
mount_nfs(8), but not suppressed by umount(8). It can be suppressed by 
rpc.umntall(8).

The same anomaly appears on stable/11 after upgrading to svn 312950.

It is relatively easy to trace this anomaly to r308871 on current and 
its MFHs (r309517 for stable/11).

Patching sbin/umount/umount.c to restore the RPC call for NFSv4 makes 
umount(8) suppress the mounttab entry as before.

I do not know what is the proper solution, as suppressing the 
modification of mounttab by mount_nfs(8) for NFSv4 could be an (more 
complicated) alternative !

Thanks for your attention,

Claude Buisson