udev rule executed too early? about autorandr

[phillipberndt]

Seems like it is. Maybe it suffices to run xrandr -q twice in a row? However, if what you're after is delaying autorandr execution by some seconds:

udev kills external processes after some time, so we cannot sleep for long times. Using systemd might be an option: We can generate a device unit using an udev rule that "wants" the autorandr service unit to run. Of course, we'd have to change the unit file to RemainAfterExit=no then.

(I have never used that feature before, so I'd have to look into this as well.)

[phillipberndt]

Here's a simple workaround: In the predetect branch, I've added support for a new script hook, predetect, which is run before autorandr calls xrandr to detect the current config. You can simply put a sleep 1 inside there, or another xrandr -q. As mentioned above, it might happen that udev kills autorandr while it sleeps.

Is this a viable solution for the problems you're experiencing?

[phillipberndt]

Regarding my earlier suggestion: I just attempted to do it that way. That doesn't work: At least with my Intel card, I only receive CHANGE events in udev, not additions and removal of devices. At the first change after installing the udev rule, systemd creates a device unit, but for every later change, it just does nothing. 😞

But we could combine both ideas. See the systemd-change branch: I now invoke the systemd unit from the udev rule. This way, the timeout from udev does not apply and you can safely use a predetect script to wait a few seconds.

@phillipberndt

But we could combine both ideas. See the systemd-change branch: I now invoke the systemd unit from the udev rule. This way, the timeout from udev does not apply and you can safely use a predetect script to wait a few seconds.

Hi. On NixOS distro, having an udev rule which invokes autorandr systemd unit breaks systemd-udev-settle service at computer boot. Do you have an idea why it may happen? Thanks.

[phillipberndt]

Breaks in which sense? Does it hang? Does it help to edit the udev rule to execute

/bin/sh -c "systemctl is-active -q systemd-udev-trigger.service && systemctl start autorandr.service"

instead of running autorandr directly? (systemd-udev-trigger.service activates systemd-udev-settle service, so this change should modify the rule such that it becomes inactive until systemd-udev-settle service is loaded.)

@phillipberndt At the computer boot at some stage a message A start job is running for udev wait for Complete Device Initialization (..s / 3min) appears and the boot pauses for ~2min.

Thank you! Your rule helps, though only after changing systemd-udev-trigger.service to systemd-udev-settle.service

Failure log:

$ systemctl status autorandr
* autorandr.service - autorandr execution hook
   Loaded: loaded (/nix/store/77dn24rn9bsd78z4w4xwi66zm5hxw9qa-autorandr-unstable-2017-01-22/lib/systemd/system/autorandr.service; linked; vendor preset: enabled)
   Active: inactive (dead)

May 31 17:22:30 nixos systemd[1]: Starting autorandr execution hook...
May 31 17:22:31 nixos systemd[1]: Started autorandr execution hook.
May 31 17:22:31 nixos systemd[1]: Starting autorandr execution hook...
May 31 17:22:31 nixos systemd[1]: Started autorandr execution hook.
May 31 17:22:31 nixos systemd[1]: Starting autorandr execution hook...
May 31 17:22:31 nixos systemd[1]: Started autorandr execution hook.
May 31 17:22:31 nixos systemd[1]: Starting autorandr execution hook...
May 31 17:22:31 nixos systemd[1]: Started autorandr execution hook.
May 31 17:22:31 nixos systemd[1]: Starting autorandr execution hook...
May 31 17:22:31 nixos systemd[1]: Started autorandr execution hook.

$ systemctl status systemd-udev-settle
* systemd-udev-settle.service - udev Wait for Complete Device Initialization
   Loaded: loaded (/nix/store/px7a1kq4prjzw17c9pppssdmibqqdm2p-systemd-232/example/systemd/system/systemd-udev-settle.service; linked; vendor preset: enabled)
   Active: failed (Result: exit-code) since Wed 2017-05-31 17:22:30 MSK; 3min 24s ago
     Docs: man:udev(7)
           man:systemd-udevd.service(8)
  Process: 463 ExecStart=/nix/store/px7a1kq4prjzw17c9pppssdmibqqdm2p-systemd-232/bin/udevadm settle (code=exited, status=1/FAILURE)
 Main PID: 463 (code=exited, status=1/FAILURE)

May 31 17:22:30 nixos systemd[1]: systemd-udev-settle.service: Main process exited, code=exited, status=1/FAILURE
May 31 17:22:30 nixos systemd[1]: Failed to start udev Wait for Complete Device Initialization.
May 31 17:22:30 nixos systemd[1]: systemd-udev-settle.service: Unit entered failed state.
May 31 17:22:30 nixos systemd[1]: systemd-udev-settle.service: Failed with result 'exit-code'.

Success boot after switching to your rule (slighly modified as I wrote earlier):

$ systemctl status autorandr
* autorandr.service - autorandr execution hook
   Loaded: loaded (/nix/store/0ms7s92l654jdhwnlxbfg61a5chrvqw9-autorandr-unstable-2017-01-22/lib/systemd/system/autorandr.service; linked; vendor preset: enabled)
   Active: inactive (dead)

$ systemctl status systemd-udev-settle
* systemd-udev-settle.service - udev Wait for Complete Device Initialization
   Loaded: loaded (/nix/store/px7a1kq4prjzw17c9pppssdmibqqdm2p-systemd-232/example/systemd/system/systemd-udev-settle.service; linked; vendor preset: enabled)
   Active: active (exited) since Wed 2017-05-31 17:28:14 MSK; 35s ago
     Docs: man:udev(7)
           man:systemd-udevd.service(8)
  Process: 454 ExecStart=/nix/store/px7a1kq4prjzw17c9pppssdmibqqdm2p-systemd-232/bin/udevadm settle (code=exited, status=0/SUCCESS)
 Main PID: 454 (code=exited, status=0/SUCCESS)
    Tasks: 0 (limit: 4915)
   CGroup: /system.slice/systemd-udev-settle.service

Auto-switching outputs on monitor hotplug works.
Would you like to add the fix to your repo or should I add it to the distro package instead?

[phillipberndt]

Thank you! Your rule helps, though only after changing systemd-udev-trigger.service to systemd-
udev-settle.service

The problem with that is that systemd-udev-settle is apparently never activated unless it is needed (Does systemctl list-dependencies --reverse systemd-udev-settle.service show services on your system?), so unless your system actually uses systemd-udev-settle, adding this change to autorandr would break the udev rule for other users. (At least Mint is affected.)

If we can find a way to reliably detect whether this fix is required, I'll add the necessary changes to the Makefile, otherwise, I'd prefer if you'd fix this downstream :-)

@phillipberndt
Thank you! You're absolutely right, it has only one service that depends on it

systemd-udev-settle.service
● └─display-manager.service

which exists only in this distro. I will make a downstream fix. Thank you much for your knowledge and help! :)

@phillipberndt Hi again! NixOS people suggested the following universal udev rule ACTION=="change", SUBSYSTEM=="drm", TAG+="systemd", ENV{SYSTEMD_WANTS}="autorandr.service" What do you think? Ok for upstream?

[phillipberndt]

I expected this rule to lead to autorandr being executed only once, instead of each time a screen is attached/removed. Have you tested that this does indeed still work? If it does, then this would be a great alternative, sure.

@phillipberndt Did a better testing and yes, you're right. Sorry then :-)

[phillipberndt]

FYI, the suggestions by @Mic92 sound good to me. If they work as expected please let me know, I'll include them upstream.

@phillipberndt

set BindsTo to the device node to systemd to make the service restart

I didn't get this. Don't we all use different devices?

As for second suggestion systemctl start --no-block autorandr.service, it works fine :-)

[phillipberndt]

I didn't get this. Don't we all use different devices?

You can refer to the instance name using "%i", e.g., have a look at "[email protected]". (This would probably be a neater solution, I'm fine with the --no-block variant though. Let me know if you don't like to take the time to test the alternative..)

@phillipberndt

¯_(ツ)_/¯ No success with that.

At first ACTION=="change", SUBSYSTEM=="drm", TAG+="systemd", ENV{SYSTEMD_WANTS}="autorandr@%E{DEVNAME}.service" didn't work because it generates SYSTEMD_WANTS=autorandr@/dev/dri/card0, but by some reason systemd doesn't strip prefix /, so BindsTo=%i.device generates -dev-dri-card0.device instead of dev-dri-card0.device. This was fixed by using ENV{SYSTEMD_WANTS}="autorandr@sys$devpath.service or ENV{SYSTEMD_WANTS}="autorandr@dev/$name.service, however the hotplug doesn't work. Statuses look ok.

$ udevadm monitor -p --subsystem=drm
UDEV  [138.264154] change   /devices/pci0000:00/0000:00:02.0/drm/card0 (drm)
ACTION=change
DEVNAME=/dev/dri/card0
DEVPATH=/devices/pci0000:00/0000:00:02.0/drm/card0
DEVTYPE=drm_minor
HOTPLUG=1
ID_FOR_SEAT=drm-pci-0000_00_02_0
ID_PATH=pci-0000:00:02.0
ID_PATH_TAG=pci-0000_00_02_0
MAJOR=226
MINOR=0
PATH=/nix/store/xh8dj5l8k64y6w3snq3srgl4cr0c3jhb-udev-path/bin:/nix/store/xh8dj5l8k64y6w3snq3srgl4cr0c3jhb-udev-path/sbin
SEQNUM=2017
SUBSYSTEM=drm
SYSTEMD_WANTS=autorandr@sys/devices/pci0000:00/0000:00:02.0/drm/card0.service
TAGS=:seat:systemd:master-of-seat:uaccess:
USEC_INITIALIZED=9905706

$ systemctl status autorandr@sys/devices/pci0000:00/0000:00:02.0/drm/card0.service
* autorandr@sys-devices-pci0000:00-0000:00:02.0-drm-card0.service - test sys-devices-pci0000:00-0000:00:02.0-drm-card0
   Loaded: loaded (/nix/store/06wk3nwm8c8828f9sld8ff6mfka2rxq4-autorandr-unstable-2017-04-16/lib/systemd/system/[email protected]; enabled; vendor preset: enabled)
  Drop-In: /nix/store/16rlpf249h5y0p32h8n829lklbd4jknm-system-units/[email protected]
           `-overrides.conf
   Active: inactive (dead) since Tue 2017-06-06 17:28:01 MSK; 24min ago
  Process: 774 ExecStart=/nix/store/06wk3nwm8c8828f9sld8ff6mfka2rxq4-autorandr-unstable-2017-04-16/bin/autorandr --batch --change --default default (code=exited, status=0/SUCCESS)
 Main PID: 774 (code=exited, status=0/SUCCESS)

Jun 06 17:28:00 nixos systemd[1]: Starting test sys-devices-pci0000:00-0000:00:02.0-drm-card0...
Jun 06 17:28:01 nixos systemd[1]: Started test sys-devices-pci0000:00-0000:00:02.0-drm-card0.

$ systemctl status sys-devices-pci0000:00-0000:00:02.0-drm-card0.device
● sys-devices-pci0000:00-0000:00:02.0-drm-card0.device - /sys/devices/pci0000:00/0000:00:02.0/drm/card0
   Loaded: loaded
   Active: active (plugged) since Tue 2017-06-06 17:27:58 MSK; 26min ago
   Device: /sys/devices/pci0000:00/0000:00:02.0/drm/card0

[phillipberndt]

Let's stick with the --no-block then. (Let me know if you'd like me to add this; otherwise, I'll wait for a PR.)

@phillipberndt Yes, please add :-) Since it's a tiny change I'll only slowdown the process. Thank you!

[phillipberndt]

Alright. Added & published as autorandr 1.1. Thanks for your help!

@phillipberndt Great, thank you much! :)

[Mic92]

It could be still possible to also encode device dependencies into the service by using:

$ systemd-escape /sys/devices/pci0000:00/0000:00:02.0/drm/card0
-sys-devices-pci0000:00-0000:00:02.0-drm-card0
$ systemctl start autorandr@$(systemd-escape /sys/devices/pci0000:00/0000:00:02.0/drm/card0)

But the current solution might be good enough for the moment.