disk_io incompatible with LVM

following our last discussion about LVM compatibility, here follows my system configuration:

(disk_io should read from /sys/block/dm-0, setting MONITORED_DISK doesn't work because it don't find it in mtab)

$ sh -x /usr/local/lib/byobu/disk_io

+ PKG=byobu
+ DATA=/u/uqn7/.byobu
+ color
+ '[' '' = 1 ']'
+ ICON_RD='<'
+ '[' '' = 1 ']'
+ ICON_WR='>'
+ '[' -z '' ']'
+ MP=/
+ case $MP in
++ grep -m 1 ' / ' /etc/mtab
++ sed -e 's: .*$::'
+ disk=/dev/mapper/ROOTVG-LVROOT
++ echo /dev/mapper/ROOTVG-LVROOT
++ sed -e 's: .*$::' -e 's:^.*/::' -e 's:\([hsv]d[a-z]\)[0-9]*$:\1:'
+ disk=ROOTVG-LVROOT
+ '[' '' = --detail ']'
+ '[' -d /var/run/screen/S-uqn7 ']'
+ DIR=/u/uqn7/.byobu
++ date +%s
+ t2=1298384278
+ for i in '"read"' '"write"'
+ cache=/u/uqn7/.byobu/byobu.disk_read
++ stat -c %Y /u/uqn7/.byobu/byobu.disk_read
+ t1=1298384274
+ unit=kB/s
+ '[' 1298384278 -le 1298384274 ']'
++ cat /u/uqn7/.byobu/byobu.disk_read
+ x1=
+ '[' read = read ']'
+ symbol='<'
++ awk '{print $3}' /sys/block/ROOTVG-LVROOT/stat
awk: cmd. line:1: fatal: cannot open file `/sys/block/ROOTVG-LVROOT/stat' for reading (No such file or directory)
+ x2=
+ echo ''
++ echo 1298384274 1298384278 '' ''
++ awk '{printf "%.0f", ($4 - $3) / ($2 - $1) * 512 / 1024 }'
+ rate=0
+ '[' 0 -lt 0 ']'
+ '[' 0 -gt 1024 ']'
++ color b M W
++ true
++ color -
++ true
++ color M W
++ true
++ color -
++ true
+ printf '<0kB/s '
+ for i in '"read"' '"write"'
+ cache=/u/uqn7/.byobu/byobu.disk_write
++ stat -c %Y /u/uqn7/.byobu/byobu.disk_write
+ t1=1298384275
+ unit=kB/s
+ '[' 1298384278 -le 1298384275 ']'
++ cat /u/uqn7/.byobu/byobu.disk_write
+ x1=
+ '[' write = read ']'
+ symbol='>'
++ awk '{print $7}' /sys/block/ROOTVG-LVROOT/stat
awk: cmd. line:1: fatal: cannot open file `/sys/block/ROOTVG-LVROOT/stat' for reading (No such file or directory)
+ x2=
+ echo ''
++ echo 1298384275 1298384278 '' ''
++ awk '{printf "%.0f", ($4 - $3) / ($2 - $1) * 512 / 1024 }'
+ rate=0
+ '[' 0 -lt 0 ']'
+ '[' 0 -gt 1024 ']'
++ color b M W
++ true
++ color -
++ true
++ color M W
++ true
++ color -
++ true
+ printf '>0kB/s '

$ cat /etc/mtab | grep '/ '
/dev/mapper/ROOTVG-LVROOT / ext3 rw 0 0

$ sudo /sbin/lvm lvdisplay
  --- Logical volume ---
  LV Name /dev/ROOTVG/LVROOT
  VG Name ROOTVG
  LV UUID erMVk8-D7o9-PaYD-j5jl-9kES-6N2H-utym66
  LV Write Access read/write
  LV Status available
  # open 1
  LV Size 20.00 GB
  Current LE 640
  Segments 1
  Allocation inherit
  Read ahead sectors auto
  - currently set to 256
  Block device 253:0

  --- Logical volume ---
  LV Name /dev/ROOTVG/LVWORK
  VG Name ROOTVG
  LV UUID AuNIqo-Af5c-XDZw-Mg7F-OIP0-vIZq-8FxJ4n
  LV Write Access read/write
  LV Status available
  # open 1
  LV Size 50.41 GB
  Current LE 1613
  Segments 1
  Allocation inherit
  Read ahead sectors auto
  - currently set to 256
  Block device 253:1

  --- Logical volume ---
  LV Name /dev/ROOTVG/LVSWAP
  VG Name ROOTVG
  LV UUID lAsNlZ-s8eL-SPGW-pzWK-Tivm-PWWF-8tFwoP
  LV Write Access read/write
  LV Status available
  # open 1
  LV Size 4.00 GB
  Current LE 128
  Segments 1
  Allocation inherit
  Read ahead sectors auto
  - currently set to 256
  Block device 253:2

$ cat /proc/partitions
major minor #blocks name

   8 0 78149687 sda
   8 1 104391 sda1
   8 2 78043770 sda2
 253 0 20971520 dm-0
 253 1 52854784 dm-1
 253 2 4194304 dm-2