[systemd-devel] ConditionPathExists vs mount unit

[Böszörményi Zoltán]

2020. 08. 10. 20:08 keltezéssel, Lennart Poettering írta:
> On Mo, 10.08.20 19:46, Böszörményi Zoltán (zboszor at pr.hu) wrote:
> 
>> Is there a way to describe optional mounts via such Conditions* options?
> 
> No.
> 
> .mount units automatically gain dependencies on the devices they are
> mounted from. Only after all dependencies are fulfilled (i.e. the
> backing device showed up) the mount is executed, and as first step of
> that the conditions are checked, i.e. much too late for your case.
> 
> My recommendation to you: write a generator, see
> systemd.generator(7) for details. The existing
> systemd-gpt-auto-generator(8) does pretty much what you want to do
> already, maybe use that as inspiration. It only supports GPT disk
> images however, and it auto-detects /var/ partitions only since v245.
> 
> Generators run very very early at boot and generate units and
> dependencies. this is where you should genreate your var.mount
> depending on the partition table. But note you have to implement that
> very carefuly, and do raw disk accesses, since udev and such is not
> running that early, nor do you even have the guarantee the kernel
> itself noticed your extra partition or not yet. The only guarantee you
> get is that the root partition was already found, everything else
> might happen concurrently.

Thanks, I will look into it.

> 
> Lennart
> 
> --
> Lennart Poettering, Berlin
>