bug#21011: df utility

[erbenton]

df (GNU coreutils) 8.21
OpenSuse 13.1

~>cd  $HOME
~> df -x debugfs
df: ‘/sys/kernel/debug/tracing’: Permission denied
Filesystem     1K-blocks     Used Available Use% Mounted on
devtmpfs         4021028       16   4021012   1% /dev
tmpfs            4034396      100   4034296   1% /dev/shm
tmpfs            4034396     5912   4028484   1% /run
/dev/sda3      237244096 37633792 187535964  17% /
tmpfs            4034396        0   4034396   0% /sys/fs/cgroup
tmpfs            4034396     5912   4028484   1% /var/run
tmpfs            4034396     5912   4028484   1% /var/lock
/dev/sda1         488613    85005    373861  19% /boot

Still the same issue, using df from a non-root account always results
in permission denied warning which messes with scripts that use df.
strace shows that even with -x debugfs or -x sysfs that df is still probing /sys
Also, TYPE's used with -x are not listed in the man page nor shown with
--help. It seems -T should show the TYPE's acceptable to df?

> df -T /sys
Filesystem     Type  1K-blocks  Used Available Use% Mounted on
sysfs          sysfs         0     0         0    - /sys

The above shows that the TYPE for /sys is sysfs but -x sysfs does not ignore that tree
it seems it only suppresses printing of the results. You can see this in the strace
~> df -T
df: ‘/sys/kernel/debug/tracing’: Permission denied
Filesystem     Type     1K-blocks     Used Available Use% Mounted on
devtmpfs       devtmpfs   4021028       16   4021012   1% /dev
tmpfs          tmpfs      4034396      100   4034296   1% /dev/shm
tmpfs          tmpfs      4034396     5912   4028484   1% /run
/dev/sda3      ext4     237244096 37633824 187535932  17% /
tmpfs          tmpfs      4034396        0   4034396   0% /sys/fs/cgroup
tmpfs          tmpfs      4034396     5912   4028484   1% /var/run
tmpfs          tmpfs      4034396     5912   4028484   1% /var/lock
/dev/sda1      ext4        488613    85005    373861  19% /boot

~> df -T -x sysfs -x debugfs -x tmpfs

df: ‘/sys/kernel/debug/tracing’: Permission denied
Filesystem     1K-blocks     Used Available Use% Mounted on
devtmpfs         4021028       16   4021012   1% /dev
/dev/sda3      237244096 37633908 187535848  17% /
/dev/sda1         488613    85005    373861  19% /boot

I have attached an strace of the following:

strace df -x sysfs -x debugfs -x tmpfs

- see attachment

df_strace.txt
Description: Text document