[Bug 1276197] [NEW] df isn't showing the correct available space as root if blocks are reserved

[Sworddragon]

Public bug reported:

I'm using Ubuntu 14.04 dev with coreutils 8.21-1ubuntu4 and if blocks
are reserved (at default 5% on ext4) and df is executed as root it shows
the available space excluding the reserved blocks. But as root is able
to write to the reserved blocks df should also show these space as
available space. Here is an example:

root at ubuntu:~# dumpe2fs -h /dev/sda1 | grep 'Reserved block count:'
dumpe2fs 1.42.9 (28-Dec-2013)
Reserved block count:     0
root at ubuntu:~# df /dev/sda1
Filesystem     1K-blocks     Used Available Use% Mounted on
/dev/sda1      144684684 82382148  62286152  57% /
root at ubuntu:~# tune2fs -r 262144 /dev/sda1
tune2fs 1.42.9 (28-Dec-2013)
Setting reserved blocks count to 262144
root at ubuntu:~# df /dev/sda1
Filesystem     1K-blocks     Used Available Use% Mounted on
/dev/sda1      144684684 82382148  61237576  58% /


For example a 4 TiB partition would use at default 200 GiB as reserved space. As soon as 3.8 GiB are full df will show as root that there is no available space anymore while root can still write 200 GiB to the partition. Not to know then the 200 GiB will end is a problem here.

** Affects: coreutils (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1276197

Title:
  df isn't showing the correct available space as root if blocks are
  reserved

Status in “coreutils” package in Ubuntu:
  New

Bug description:
  I'm using Ubuntu 14.04 dev with coreutils 8.21-1ubuntu4 and if blocks
  are reserved (at default 5% on ext4) and df is executed as root it
  shows the available space excluding the reserved blocks. But as root
  is able to write to the reserved blocks df should also show these
  space as available space. Here is an example:

  root at ubuntu:~# dumpe2fs -h /dev/sda1 | grep 'Reserved block count:'
  dumpe2fs 1.42.9 (28-Dec-2013)
  Reserved block count:     0
  root at ubuntu:~# df /dev/sda1
  Filesystem     1K-blocks     Used Available Use% Mounted on
  /dev/sda1      144684684 82382148  62286152  57% /
  root at ubuntu:~# tune2fs -r 262144 /dev/sda1
  tune2fs 1.42.9 (28-Dec-2013)
  Setting reserved blocks count to 262144
  root at ubuntu:~# df /dev/sda1
  Filesystem     1K-blocks     Used Available Use% Mounted on
  /dev/sda1      144684684 82382148  61237576  58% /

  
  For example a 4 TiB partition would use at default 200 GiB as reserved space. As soon as 3.8 GiB are full df will show as root that there is no available space anymore while root can still write 200 GiB to the partition. Not to know then the 200 GiB will end is a problem here.

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