union mount after nfs mount

[Marc Balmer <marc_(_at_)_msys_(_dot_)_ch>]

Hi All

I am trying to share an OpenBSD source tree via NFS.  To do so, I mount the src tree read only from a server and then I do a union mount of the NFS mounted filesystem and a local directory:

mkdir /usr/src
mkdir /usr/obj
mkdir /net/server/usr/src
mount -t nfs -o ro server:/usr/src /net/server/usr/src
mount -t union -o -b /net/server/usr/src /usr/src

Then I try to "make obj" in /usr/src, which strangely fails with the following error:

# make obj
===> lib
===> lib/csu
make: No such file or directory.
*** Error code 2
 
Stop in /usr/src/lib.
*** Error code 1
 
Stop in /usr/src.
#

Did I miss some semantic details of nfs or union mounts (perhaps the fine print...)?

Regards,
Marc