[Bug 1980991] [NEW] /usr/sbin/on_ac_power incorrectly reporting ac power status

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Ghadi Rahme (ghadi-rahme):

Thank you @kevintate for the original bug report.

[Impact]

Currently there is an issue with the ac_on_power script where it thinks that USB-c ports with devices plugged in to them are plugged in to power. This is because the script does not check first if these usb-c ports are in sink or source mode first.
The solution is to check /sys/class/typec/* for the mode these usb ports are in, and ignore them if none of them are running in source mode.
This is causing tools such as unattended-upgrades to fail to run because on_ac_power is miss reporting the power state of the machine.  

[Test Plan]

Part 1: Verifying if the script returns the correct result

On a device with a USB-c port (it does not matter if the port can be
used for powering the device or not) run the following test:

1. Install the patched version of on_ac_power

2. run: $ on_ac_power

3. check the return value: $ echo $?

4. check the return value based on different scenarios:
- plugged in using usb-c
- plugged in using another non usb port
- not plugged it at all
- with a usb-c device plugged in that does not deliver power to the machine
- with a graphics card or any other PCIE device that happen to have a usb-c port (this with and without a usb-c device connected to this extra port)

compare the return value with the actual state of the machine. If the
machine is not plugged in to power, you should expect 0 as the return
code.

If the machine is plugged in then the return code should be 1.

If you receive 255 as an return code then the script was unable to
determine the power profile of the machine and is related to the kernel
not exposing enough information to user space. Consumers of on_ac_power
generally consider such a return code as the machine being plugged in to
power.

Part2: verifying that no regressions exist with consumers such as
unattended-upgrades

One such consumer is unattended-upgrades. To verify if unattended
upgrades is still affected by this issue, run the following steps:

1. first make sure unattended upgrades is installed:
$ sudo apt install unattended-upgrades

2. using the default config run the following command under different power scenarios:
$ sudo unattended-upgrade --dry-run -v
The different power scenarios to test for are:
- plugged in using usb-c
- plugged in using another non usb port
- not plugged it at all
- with a usb-c device plugged in that does not deliver power to the machine
- with a graphics card or any other PCIE device that happen to have a usb-c port (this with and without a usb-c device connected to this extra port)

3. Make sure that the command above returns the correct result for each
status, for example when the machine is expected to be on main power,
the following output should be returned:

ghadi at XPS-17-9720 ~ » sudo unattended-upgrades --dry-run -v
Starting unattended upgrades script
Allowed origins are: o=Ubuntu,a=noble, o=Ubuntu,a=noble-security, o=UbuntuESMApps,a=noble-apps-security, o=UbuntuESM,a=noble-infra-security
Initial blacklist: 
Initial whitelist (not strict): 
No packages found that can be upgraded unattended and no pending auto-removals
The list of kept packages can't be calculated in dry-run mode.

If the machine is not getting power from main but from it's battery, the
following output should be seen:

ghadi at XPS-17-9720 ~ » sudo unattended-upgrades --dry-run -v
System is on battery power, stopping

Part3: Test plan conclusions

If the tests done in part 1 fail, this would mean that the proposed fix was not enough to resolve the issue. 
If part 2 fails but part 1 passes, further investigations are needed into unattended-upgrades for why it's result might differ from on_ac_power.

[Where problems could occur]

* the script could still incorrectly return the state of power of the machine, specially if the kernel incorrectly advertises a usbc port to be in a different mode then it is in.
* Packages that depend on on_ac_power might fail to run or execute if they require the machine to be in a specific power state first, unattended-upgrades and anacron are two example packages.

[Original Description]
Good afternoon, folks.

I believe I discovered a bug in the /usr/sbin/on_ac_power script. I have
a Dell OptiPlex 5090 host that has an entry in /sys/class/power_supply
for "ucsi-source-psy-USBC000:001". I believe this is the USB-C power
delivery port on the front of the chassis. The issue I'm encountering is
that /usr/sbin/on_ac_power is exiting with code 1 which states: (1
(false) if not on AC power) when that isn't the case.

This looks to be because of the ucsi-source-psy-USBC000:001 entry
reporting the "online" status as 0, presumably because nothing is
currently connected to that USB-C port.

This causes /usr/sbin/on_ac_power to incorrectly report that the machine
isn't connected to AC power and causes other utilities like unattended-
upgrades to quit when using the default configuration since it believes
the machine isn't connected to AC power.

There is a workaround with unattended-upgrades where you can specify it
to run regardless of if AC power is connected, but as more and more
chassis implement power-delivery USB-C ports I foresee this becoming
more of an issue.

I'm not sure if it's anything to look into, but I figured I would share
my findings. Please let me know if you have any questions or if I can
provide any additional information, troubleshooting, or testing.

Thanks!
-Kevin

** Affects: powermgmt-base (Ubuntu)
     Importance: High
     Assignee: Ghadi Rahme (ghadi-rahme)
         Status: In Progress

** Affects: powermgmt-base (Ubuntu Focal)
     Importance: Undecided
     Assignee: Ghadi Rahme (ghadi-rahme)
         Status: In Progress

** Affects: powermgmt-base (Ubuntu Jammy)
     Importance: Undecided
     Assignee: Ghadi Rahme (ghadi-rahme)
         Status: In Progress

** Affects: powermgmt-base (Ubuntu Kinetic)
     Importance: High
         Status: Won't Fix

** Affects: powermgmt-base (Ubuntu Lunar)
     Importance: High
         Status: Won't Fix

** Affects: powermgmt-base (Ubuntu Mantic)
     Importance: High
     Assignee: Ghadi Rahme (ghadi-rahme)
         Status: Won't Fix

** Affects: powermgmt-base (Ubuntu Noble)
     Importance: High
     Assignee: Ghadi Rahme (ghadi-rahme)
         Status: In Progress

** Affects: powermgmt-base (Ubuntu Oracular)
     Importance: High
     Assignee: Ghadi Rahme (ghadi-rahme)
         Status: In Progress

** Affects: powermgmt-base (Ubuntu Plucky)
     Importance: High
     Assignee: Ghadi Rahme (ghadi-rahme)
         Status: In Progress

** Affects: powermgmt-base (Debian)
     Importance: Unknown
         Status: Fix Released


** Tags: foundations-todo fr-2548
-- 
/usr/sbin/on_ac_power incorrectly reporting ac power status
https://bugs.launchpad.net/bugs/1980991
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