Re: [OE-core][PATCH V2] systemd: do not delete systemd-getty-generator

[ChenQi <Qi.Chen@windriver.com>]

On 3/26/25 01:50, Ross Burton wrote:
> On 19 Mar 2025, at 06:40, Qi.Chen@windriver.com wrote:
>> Some BSPs don't set SERIAL_CONSOLES. They need systemd-getty-generator[1]
>> be there to work. This generator has been there for a few previous
>> releases, we don't see any problem it brings up. So let's keep it.
> This is a wonderfully convoluted and not-by-design situation.  Looking at eg, styhead.  The getty generator isn’t enabled by default:
>
> $ bitbake-getvar --value -r systemd PACKAGECONFIG|grep getty || echo not found
> not found
>
> In styhead if the getty generator isn’t enabled then we delete the serial-getty units that the generator would create symlinks to, so the generator can’t work.
>
> if ${@bb.utils.contains('PACKAGECONFIG', 'serial-getty-generator', 'false', 'true', d)}; then
>      # Provided by a separate recipe
>      rm ${D}${systemd_system_unitdir}/serial-getty* -f
> fi
>
> If the generator is disabled then systemd depends on the systemd-serialgetty recipe which creates explicit links for the consoles in SERIAL_CONSOLES.  This recipe in styhead also ships a serial-getty@.service unit template, but the package should be empty if SERIAL_CONSOLES isn’t set.  However, the recipe itself has a default value (SERIAL_CONSOLES ?= "115200;ttyS0”) which provides a value if the BSP doesn’t set it, so the unit files do get installed after all.
>
> I think that your setup potentially doesn’t actually use the getty generator at all, but the bad default of ttyS0 from the systemd-serialgetty recipe.  This no longer exists as the recipe doesn’t set its own default anymore (as, I believe, is correct).
>
> Can you have a look at your actual use case?  I wouldn’t be surprised if it’s actually just using ttyS0 from the configuration, and the BSP could just set that.

The BSP is using the generator. See output below:

root@xilinx-zynqmp:~# ls -l /run/systemd/generator/getty.target.wants/*
lrwxrwxrwx 1 root root 41 Mar 28 01:00 
/run/systemd/generator/getty.target.wants/serial-getty@ttyPS0.service -> 
/lib/systemd/system/serial-getty@.service
root@xilinx-zynqmp:~#

I think the generator took effect for previous releases because, as you 
said, the systemd-serialgetty@.service template was always installed (by 
a lucky mistake that you've now fixed) and the systemd-getty-generator 
was always installed.

Now, in master branch, this template is always installed too. But we'll 
also need the systemd-getty-generator to be there to do autodetection 
for some BSPs.

Regards,
Qi

>
> In the medium term I really do want to propose switching from SERIAL_CONSOLES to auto-detection by default, but this involves making the same thing idea on sysvinit which is more involved.  I _almost_ have it working, but it didn’t get working in time for M3.
>
> Ross