HEAD: no rootfs in jail

[YONETANI Tomokazu <qhwt+dfly@xxxxxxxxxx>]

Hello.
I don't remember when I started seeing this, but `df' doesn't show
the rootfs from inside jail, but any other mountpoints are visible.

# jls
JID     Hostname        Path    IPs
1       j0      /home/j0        192.168.2.251
# jexec 1 df
(nothing shows up)
# jexec 1 ls -l /
total 13946
-rw-r--r--   2 root  wheel       881 Aug  5 00:52 .cshrc
-rw-r--r--   2 root  wheel       914 Aug  5 00:53 .profile
-r--r--r--   1 root  wheel      6896 Jul 18  2006 COPYRIGHT
drwxr-xr-x   2 root  wheel      1024 Jan 17 17:09 bin
drwxr-xr-x   3 root  wheel       512 Jan 17 17:11 boot
drwxr-xr-x   3 root  wheel     24064 Jul 18  2006 dev
drwxr-xr-x  17 root  wheel      2048 Jan 18 16:23 etc
drwxr-xr-x   4 root  wheel       512 Aug  5 00:37 home
drwxr-xr-x   2 root  wheel       512 Jun 14  2005 mnt
dr-xr-xr-x   2 root  wheel       512 Jun 14  2005 proc
drwxr-xr-x   3 root  wheel       512 Jan 18 16:22 root
drwxr-xr-x   2 root  wheel      2048 Jan 17 17:10 sbin
drwxr-xr-x   3 root  wheel       512 Jul 18  2006 smp
lrwxr-xr-x   1 root  wheel        11 Jan 17 17:09 sys -> usr/src/sys
drwxrwxrwt   2 root  wheel      2048 Jan 19 03:01 tmp
drwxr-xr-x   4 root  wheel       512 Jan 18 03:03 u
drwxr-xr-x  14 root  wheel       512 Jan 18 03:03 usr
drwxr-xr-x  21 root  wheel       512 Jun 14  2005 var

# jexec 1 md5 /bin/df ; md5 /bin/df
MD5 (/bin/df) = a0327cd000b1d85b83766557b79500b2
MD5 (/bin/df) = a0327cd000b1d85b83766557b79500b2

# mount -tnull /home/source /home/j0/home/source
# jexec 1 df
Filesystem   1K-blocks     Used    Avail Capacity  Mounted on
/home/source  32350786 18819430 10943294    63%    /home/source

I haven't noticed any other problem, just that rootfs doesn't show
the rootfs for the jail.  I also tried setting up a faked /etc/fstab
in jail, but it had no effect.

Regards.