bug#52654: shepherd lacks error reporting

[raingloom]

On Sun, 19 Dec 2021 06:13:20 +0100
raingloom <raingloom@riseup.net> wrote:

> I'm writing a single-shot shepherd-service that expands the (ext4)
> root file system on first boot, using the hostname service as a
> template, just passing the script as a G-expression, instead of using
> the forkexec constructor.
> Of course there is a bug in it. Trouble is, I have no idea what it is,
> because Shepherd won't tell me. :)
> The VM boots and completes the ssh initialization phase and then
> apparently just gets stuck. Doesn't even show a login prompt.
> It's... not a great debugging experience.
> I'm going to attempt to at the very least add some error reporting.
> It would also be really nice if the failure modes for Shepherd
> services were better documented, like what happens when the procedure
> passed in the `start` field fails, or is not even a procedure, etc.
> Since I never touched Shepherd internals, help would be greatly
> appreciated.
> 
> ps.: I'm attaching the system definition for completeness's sake and
> so that someone might point out where the error is, but honestly the
> exact bug in my code does not matter for the feature. All that
> matters is there is an error and it should be logged but isn't.

So the error in my config turned out to be the G-expression not
evaluating to a lambda, but the issue with Shepherd still stands.