#[SOLVED] Changing sysfs permissions using udev rules?

63 messages · Page 1 of 1 (latest)

left shore
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I'm slightly confused what SUBSYSTEM parameter does, is it equivalent of /sys/class/SUBSYSTEM? Or is it something else?
How would I change permissions for something like ideapad_acpi? Which is not even in /sys/class, but instead in /sys/bus/platform/drivers/

terse zephyr
left shore
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It is not?

terse zephyr
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It is not, udev is only in charge of /dev.

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Files under /sys are direct kernel interfaces, created by the kernel and not affected by udev.

left shore
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What the hell is this then?
/etc/udev/rules.d/99-swayosd.rules

ACTION=="add", SUBSYSTEM=="backlight", RUN+="/bin/chgrp video /sys/class/backlight/%k/brightness"
ACTION=="add", SUBSYSTEM=="backlight", RUN+="/bin/chmod g+w /sys/class/backlight/%k/brightness"
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SwayOSD already added some rules and they apply to /sys

terse zephyr
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This is the cause, RUN+= is just the effect.

left shore
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are backlight devices in /dev? Sounds like nonsense

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Or... SUBSYSTEM is like a hook?

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triggers after certain SUBSYSTEM has initialized?

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Doesn't matter where it got mounted I assume?

terse zephyr
left shore
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Still confused

terse zephyr
# left shore Still confused

IIRC udev is part of systemd, it is not very clearly documented except in the code, I think you can find some logic from SUBSYSTEM.

left shore
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udev is also a part of initramfs which is way before pid 0 afaik?

terse zephyr
left shore
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What?

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less /etc/mkinitcpio.conf

image.png
terse zephyr
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Its source code is available under systemd/src/udev.

terse zephyr
left shore
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wdymmmmmm

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mkinitcpio isn't Arch Linux specific

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or wait

terse zephyr
left shore
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Ok but then what does hook do

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Actually, forget it

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Back to original question

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How would I change perms for ideapad_acpi

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which SUBSYSTEM is it?

terse zephyr
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                if (type == TK_M_SUBSYSTEM && STR_IN_SET(value, "subsystem", "bus", "class"))
                        match_type = MATCH_TYPE_SUBSYSTEM;
terse zephyr
left shore
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so... it's platform?

left shore
terse zephyr
left shore
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the one with some kind of id?

terse zephyr
left shore
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yes

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I want it to be available to all power group

terse zephyr
left shore
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In original title I just asked for general udev help, I wasn't sure if I'm on the right track even

terse zephyr
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What is the device name?

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It should look like this: VPC2004:00.

terse zephyr
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Albeit, if you do not want to deal with obscure udev rules, you can always use
/etc/tmpfiles.d, which is a common practice used by systemd itself
e.g.

m /sys/bus/platform/drivers/ideapad_acpi/VPC2004:00 0664 root power - -
left shore
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(udev-worker)[277]: VPC2004:00: Process '/usr/bin/chgrp power /devices/pci0000:00/0000:00:1f.0/PNP0C09:00/VPC2004:00/conservation_mode' failed with exit code 1

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works when I run manually

left shore
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Oh, nevermind

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It works

left shore
terse zephyr
# left shore It works

Usually, if there is a device event, udev can be used, otherwise use tmpfiles.d or the systemd service.

left shore
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I figured out from this page

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that I needed $sys

terse zephyr
left shore
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Now it works, thank you

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[SOLVED] Changing sysfs permissions using udev rules?

terse zephyr