mountpoint refcounting?

[Patrick Welche <prlw1%newn.cam.ac.uk@localhost>]

With an i386 kernel from Jan 31 12:22 GMT, I can boot into single user mode,
fsck -p , mount -A , then:

# mount
/dev/sd2a on / type ffs (soft dependencies, local)
/dev/sd2e on /var type ffs (soft dependencies, local)
/dev/sd2f on /home type ffs (soft dependencies, local)
/dev/sd2g on /usr type ffs (soft dependencies, local)
/dev/sd2h on /destdir type ffs (soft dependencies, local)
/dev/sd1e on /usr/obj type ffs (soft dependencies, local)
/dev/sd1f on /home/prlw1 type ffs (soft dependencies, local)
/dev/sd1i on /usr/src type ffs (soft dependencies, local)
# cd /usr/src
# umount /dev/sd1e
# newfs /dev/sd1e
newfs: /dev/sd1e: open for write: Device busy
# fstat /dev/sd1e
USER     CMD          PID   FD MOUNT       INUM MODE         SZ|DV R/W NAME
# fstat -f /usr/obj
USER     CMD          PID   FD MOUNT       INUM MODE         SZ|DV R/W


So, why is /usr/obj thought to be busy? (pwd is not in /usr/obj, and the
single user is just at the sh prompt)

Cheers,

Patrick