kern/162591: cross-filesystem nullfs does not work as expected

[mw at wzff.de]

>Number:         162591
>Category:       kern
>Synopsis:       cross-filesystem nullfs does not work as expected
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          change-request
>Submitter-Id:   current-users
>Arrival-Date:   Tue Nov 15 18:50:06 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator:     Moritz Wilhelmy
>Release:        FreeBSD 9.0-RC2 amd64
>Organization:
>Environment:
System: FreeBSD phallus.wzff.de 9.0-RC2 FreeBSD 9.0-RC2 #14: Wed Nov 9 10:27:26 UTC 2011 root at phallus.wzff.de:/usr/obj/usr/src/sys/PHALLUS amd64

>Description:
 mounting a tree with mount_nullfs does not work as expected if the
 filesystem has other nullfs filesystems mounted below. The files from the tree
 itself show up, but not the files from mountpoints under the tree. See below for
 an example.
 Expected behaviour would be that all mountpoints from the nullfs mount show up
 on the tree that it's mounted on.

>How-To-Repeat:
 My original use-case:
  # mkdir -p testdir shares/testdir somejail/shares
  # touch testdir/{moo,cow}
  # ls testdir
  cow moo
  # mount_nullfs -o ro testdir shares/testdir
  # mount_nullfs -o ro shares somejail/shares
  # ls shares/testdir/
  cow moo
  # ls somejail/shares/testdir/
  # ^^^^ no files here
>Fix:
 Unknown
>Release-Note:
>Audit-Trail:
>Unformatted: