[systemd-devel] Starting service conditionally and retrying when failure

[sdrb]

Hi,

I'd like to ask how to achieve following functionality in systemd:

I'd like to start alsa-restore.service only once just after one of the 
specified files appears. Those file matches: /dev/snd/control*.

For now I have something like this:

[Unit]
Description=Save/Restore Sound Card State
ConditionPathExistsGlob=/dev/snd/control*
After=sysinit.target

[Service]
Type=oneshot
RemainAfterExit=true
ExecStart=-/sbin/alsactl restore -f /etc/asound.state

[Install]
WantedBy=multi-user.target


but during the start when there is no any of /dev/snd/control* files - 
the condition is not meet and the service is not going up.
Those files appears later.

So that what I'd like to achieve is to wait for appearing of those files 
and then starting alsa-restore service.

Is it possible to do in systemd? If yes - how to do this?