Ben Hutchings <b...@decadent.org.uk> writes:
> I would like to address this by backporting this feature:
>
> commit d6e486868cde585842d55ba3b6ec57af090fc343
> Author: Ludwig Nussel <ludwig.nus...@suse.de>
> Date: Wed Jan 25 11:52:28 2012 +0100
>
> debugfs: add mode, uid and gid options
>
> and then changing the default mode (mask) to be 0700.
I like the proposal, but the feature does not seem mature yet. Played a
bit with it and noticed a couple of confusing bugs which IMHO should be
fixed first:
1) mode and owner is not propagated to files below the mount point:
nemi:/tmp# mount /sys/kernel/debug -o uid=42,mode=0700
nemi:/tmp# ls -la /sys/kernel/debug/
total 0
drwx------ 16 42 root 0 Jul 2 00:07 .
drwxr-xr-x 6 root root 0 Jul 2 00:07 ..
drwxr-xr-x 2 root root 0 Jul 2 00:07 acpi
drwxr-xr-x 32 root root 0 Jul 11 14:36 bdi
drwxr-xr-x 2 root root 0 Jul 13 11:51 bluetooth
drwxr-xr-x 4 root root 0 Jul 2 00:07 dri
drwxr-xr-x 2 root root 0 Jul 2 00:07 dynamic_debug
drwxr-xr-x 2 root root 0 Jul 2 00:07 extfrag
-r--r--r-- 1 root root 0 Jul 2 00:07 gpio
drwxr-xr-x 3 root root 0 Jul 2 00:07 ieee80211
drwxr-xr-x 2 root root 0 Jul 2 00:07 kprobes
drwxr-xr-x 2 root root 0 Jul 2 00:07 kvm
drwxr-xr-x 2 root root 0 Jul 2 00:07 mce
drwxr-xr-x 2 root root 0 Jul 2 00:07 regmap
-rw-r--r-- 1 root root 0 Jul 2 00:07 sched_features
-r--r--r-- 1 root root 0 Jul 2 00:07 suspend_stats
drwxr-xr-x 5 root root 0 Jul 2 00:07 tracing
drwxr-xr-x 2 root root 0 Jul 2 00:07 usb
-r--r--r-- 1 root root 0 Jul 2 00:07 wakeup_sources
drwxr-xr-x 2 root root 0 Jul 2 00:07 x86
2) ownership and mode seems to be shared amoung all mount points,
resulting in the following unexpected behaviour:
nemi:/tmp# mount /sys/kernel/debug -o uid=42,mode=0700
nemi:/tmp# ls -ld /sys/kernel/debug
drwx------ 16 42 root 0 Jul 2 00:07 /sys/kernel/debug
nemi:/tmp# mount -t debugfs none /mnt/temp -o uid=0,mode=0755
nemi:/tmp# ls -ld /sys/kernel/debug
drwxr-xr-x 16 root root 0 Jul 2 00:07 /sys/kernel/debug
3) ownership (but not mode?!) seems to be cached between mounts,
resulting in the following unexpected behaviour:
nemi:/tmp# mount /sys/kernel/debug -o uid=42,mode=0700
nemi:/tmp# ls -ld /sys/kernel/debug
drwx------ 16 42 root 0 Jul 2 00:07 /sys/kernel/debug
nemi:/tmp# umount /sys/kernel/debug
nemi:/tmp# grep debugfs /proc/mounts
nemi:/tmp# grep debugfs /etc/fstab
debug /sys/kernel/debug debugfs defaults
nemi:/tmp# mount /sys/kernel/debug
nemi:/tmp# ls -ld /sys/kernel/debug
drwxr-xr-x 16 42 root 0 Jul 2 00:07 /sys/kernel/debug
These can all be considered minor glitches, but they sure confused me
the first time I hit them.
Bjørn
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