Recent FreeBSD, NFSv4 and /var/db/mounttab

[Rick Macklem]

Claude Buisson wrote:
>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 !
This would be the correct fix. The entries in mounttab are meaningless.
Even for NFSv3, all they do is provide a "best guess" answer for
"showmount".
- The Mount protocol is not part of NFSv4. I had a patch which disabled
  it for NFSv4 servers, but some folk liked the idea of having "showmount -e"
  to work, so I didn't commit it.

rick
ps: I had actually thought mount_nfs(8) didn't do a Mount protocol RPC
      for NFSv4, but I guess it is. That needs to be fixed, since NFSv4 servers
      don't need to support Mount at all.