[systemd-devel] [Feature request] A way to native import /proc/cmdline within unit

[Gerardo Exequiel Pozzi]

On 07/29/2013 08:12 PM, Lennart Poettering wrote:
> On Thu, 25.07.13 19:35, Gerardo Exequiel Pozzi (vmlinuz386 at yahoo.com.ar) wrote:
> 
>> On 07/25/2013 05:06 PM, Lennart Poettering wrote:
>>> On Sat, 20.07.13 16:37, Gerardo Exequiel Pozzi (vmlinuz386 at yahoo.com.ar) wrote:
>>>
>>>> Hello
>>>>
>>>> I am maintainer of Archiso project (The Arch Linux live ISO creator).
>>>>
>>>> I like a feature for systemd within unit files, mainly for importing
>>>> /proc/cmdline in initramfs stage, or in a generic form for any other
>>>> file with a similar format. Something like ImportOneLineFile=, like
>>>> current EnvironmentFile=.
>>>>
>>>> In this way, we can use/pass parameters to Exec*= directives if needed.
>>>
>>> So you awant to import kernel cmdline arguments into your environment?
>>
>> Yes, in a particular unit.
>>
>>> Note that you can do that already with the systemd.setenv= kernel
>>> command line option. What else do you need?
>>>
>>
>> Yes. But doing in this way:
>>
>> * Makes each variable passed, global to all units.
>> * For each parameter that I need to process I need to prefix them.
>>
>> So for example
>> archisobasedir=arch archisolabel=ARCH_201307 checksum=y
>> becomes:
>> systemd.setenv=archisobasedir=arch
>> systemd.setenv=archisolabel=ARCH_201307 systemd.setenv=checksum=y
>>
>> And if booting via PXE, think about automatic cmdline appended by
>> "ip=..." PXELINUX/IPAPPEND...
>>
>> The other solution that I have is using a service+script for
>> parsing/dumping cmdline in a file, then import with EnvironmentFile= but
>> does not look good. Other way maybe is using a generator, but they run
>> too early and I need to wait for some things happens before generating
>> units in a dynamic way.
> 
> Hmm, but how do you process those variables further? In a shell script
> anyway? That sounds as if it would be appropriate to also parse
> /proc/cmdline from there? Why would it be better to do this in systemd
> rather than in the shell script itself?
> 
> (or similar: better than in the Pythons script itself, Perl script, C
> program ...)
> 
> Lennart
> 

In inside systemd unit, I want to avoid shell script if possible, using
units only, doing things in a "systemd way". Anyway for complex tasks
where systemd does not fit, scripting seems to be necessary.

ExecStart=/usr/bin/program --param=$CMDLINE__ARG_VALUE ...

I think is better because systemd already parse /proc/cmdline, and I
guess that implementing this is easy, but maybe I am wrong.

Thanks for your feedback.

-- 
Gerardo Exequiel Pozzi
\cos^2\alpha + \sin^2\alpha = 1

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