union-mounting mfs

[Frank Wille <frank%hasenbraten.de@localhost>]

Hi,

I wonder if this is a bug, or am I doing something wrong?
For a Compact Flash disk I want to mount an mfs with option union on top of
/var to allow writing of log files, etc. But strangely only files created in
the /var directory will appear in the mfs. When creating a file in a sub
directory, like /var/db, it will go directly to the ffs on the CF disk!

This behaviour can easily be reproduced with a union-mfs on a CD-ROM. Example:

# mount_cd9660 /dev/cd0a /cdrom
# mount_mfs -o union -s 32m test_mfs /cdrom/i386
# cp /netbsd /cdrom/i386/
# cp /netbsd /cdrom/i386/binary/kernel/
cp: /cdrom/i386/binary/kernel/netbsd: Read-only file system

The first cp works, the second doesn't, because it bypasses the mfs! Why?

This is a NetBSD 3.1.1 system (3.1 with latest patches).

-- 
Frank Wille