Multiple /dev/root in /proc/mounts output

Question

How can one explain multiple occurrence of /dev/root device containing different filesystems in /proc/mounts ?

# cat /proc/mounts
rootfs / rootfs rw 0 0
/dev/root / ext3 rw,data=ordered 0 0
/dev /dev tmpfs rw 0 0
/proc /proc proc rw 0 0
/sys /sys sysfs rw 0 0
/proc/bus/usb /proc/bus/usb usbfs rw 0 0
devpts /dev/pts devpts rw 0 0
/dev/hda1 /boot ext3 rw,data=ordered 0 0
tmpfs /dev/shm tmpfs rw 0 0
none /proc/sys/fs/binfmt_misc binfmt_misc rw 0 0
sunrpc /var/lib/nfs/rpc_pipefs rpc_pipefs rw 0 0
/etc/auto.misc /misc autofs rw,fd=7,pgrp=2161,timeout=300,minproto=5,maxproto=5,indirect 0 0
-hosts /net autofs rw,fd=13,pgrp=2161,timeout=300,minproto=5,maxproto=5,indirect 0 0
nfsd /proc/fs/nfsd nfsd rw 0 0
/dev/root /var/lib/nfs ext3 rw,data=ordered 0 0

OK. Here we have two. One for / partition (/proc/cmdline: ro root=/dev/VolGroup00/LogVol00) and one for /var/lib/nfs. BUT:

# ls -la /var/lib/nfs
total 68
drwxr-xr-x  8 root    root    4096 Aug  7 09:45 .
drwxr-xr-x 32 root    root    4096 Aug  3 09:32 ..
-rw-r--r--  1 root    root       0 Feb 25 16:26 etab
-rw-r--r--  1 root    root       0 Feb 25 16:26 rmtab
drwxr-xr-x  2 root    root    4096 Feb 25 16:26 rpc_pipefs
drwxr-xr-x  2 root    root    4096 Aug  7 08:03 sm
drwxr-xr-x  2 root    root    4096 Aug  7 08:03 sm.bak
drwxr-xr-x  4 root    root    4096 Aug  7 09:45 sm.ha
drwx------  4 rpcuser rpcuser 4096 Aug  3 06:52 statd
-rw-------  1 root    root       0 Feb 25 16:26 state
drwxr-xr-x  2 root    root    4096 Feb 25 16:26 v4recovery
-rw-r--r--  1 root    root       0 Feb 25 16:26 xtab

The contents of root filesystem and /var/lib/nfs is different. How could one block device /dev/root reflect different filesystems? And why /dev/root used for /var/lib/nfs at all?

Answer 1

Sorry for bothering you but I've fount the answer myself by accident. /etc/mtab explains things:

# cat /etc/mtab
/dev/mapper/VolGroup00-LogVol00 / ext3 rw 0 0
proc /proc proc rw 0 0
sysfs /sys sysfs rw 0 0
devpts /dev/pts devpts rw,gid=5,mode=620 0 0
/dev/hda1 /boot ext3 rw 0 0
tmpfs /dev/shm tmpfs rw 0 0
none /proc/sys/fs/binfmt_misc binfmt_misc rw 0 0
sunrpc /var/lib/nfs/rpc_pipefs rpc_pipefs rw 0 0
nfsd /proc/fs/nfsd nfsd rw 0 0
/var/lib/nfs /var/lib/nfs none rw,bind 0 0

/dev/root is also used for bind mounts. Don't ask me why /var/lib/nfs bind-mounted on top of itself :)