Tweak systemd unit definition

[sftim]

ℹ️ UNTESTED

These changes ought to make the systemd unit automatically restart (see #183), and run with extra security restrictions.
I haven't tried them though. Nonetheless I hope the PR is useful. Anyone who wants to is welcome to test this out and report back.

[dgsiegel]

Looks good! We might even make use of more systemd capabilites. Looking at start-webcam.sh, it could be easily replaces as it does three things:

1. Check if both /dev/video0 and /dev/video1 exist. Could be replaced with ConditionPathExists
2. Applying config. Could be a small shell script run with ExecStartPre
3. Running the actual uvc-gadet. Could be run with ExecStart

[dgsiegel]

@sftim wanna check these three things out?

[sftim]

I'm not going to have any time to move this PR forward with extra changes, at least not for the foreseeable. Sorry about that.
I'm happy if someone wants to open a new PR that takes my 3 commits and adds some more, or to start from scratch.

[sftim]

Whoops.

[sftim]

Even if this isn't perfect, perhaps it's OK to merge as-is? The key thing would be to verify it actually works.

[dgsiegel]

Even if this isn't perfect, perhaps it's OK to merge as-is? The key thing would be to verify it actually works.

I'd rather not merge something that wasn't verified. But you can easily use the Github Action to build your images and try those. Also you could replace squashfs with ext4 in your build, to test without having to build a new image every time.