misc/45029: Mount fails inside pnullfs hierarchy

[lolkaantimat%gmail.com@localhost]

>Number:         45029
>Category:       misc
>Synopsis:       Mount fails inside pnullfs hierarchy
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    misc-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jun 08 06:30:00 +0000 2011
>Originator:     Evgeniy Ivanov
>Release:        NetBSD 5.1_STABLE (GENERIC) #0: Tue May 17 19:27:06 MSD 2011
>Organization:
>Environment:
NetBSD  5.1_STABLE NetBSD 5.1_STABLE (GENERIC) #0: Tue May 17 19:27:06 MSD 2011 
 root@:/usr/obj/sys/arch/i386/compile/GENERIC i386
>Description:
Mount (tested from another instance of pnullfs or mount_null) fails inside 
pnullfs hierarchy. mount() sets errno to EISDIR, which is strange.

I'm willing to debug the problem, but I'm not familiar with NetBSD and don't 
know how to trace mount() call to start debugging.
>How-To-Repeat:
mkdir -p /foo/bindir/baz
mkdir /bar
mkdir /qwe

./pnullfs /foo /bar
./pnullfs /qwe /bar/bindir/baz
pnullfs: pnullfs: puffs_daemonpuffs_mount: : Is a directory

OR

./pnullfs /foo /bar
mount_null /qwe /bar/bindir/baz
mount_null: /qwe on /bar/bindir/baz: Is a directory

But works fine when both time mount_null is used. EISDIR even is not listed as 
possible mount() error.
>Fix: