shepherd: prefix output with service names?

[Ricardo Wurmus <rekado@elephly.net>]

Hi Guix,

here is some output from “guix system reconfigure”:

--8<---------------cut here---------------start------------->8---
…
activating system...
The following derivation will be built:
  /gnu/store/7361cd8aasxwwb93ygdfwjp3ghn06ahb-switch-to-system.scm.drv

building /gnu/store/7361cd8aasxwwb93ygdfwjp3ghn06ahb-switch-to-system.scm.drv...
making '/gnu/store/rp04hkqlzx5j2lhxainsz77vpqqigsjz-system' the current system...
setting up setuid programs in '/run/setuid-programs'...
populating /etc from /gnu/store/gq2dvz09wf3sdmvynr2vdzy5wwj7k9fd-etc...
The files belonging to this database system will be owned by user "postgres".
This user must also own the server process.

The database cluster will be initialized with locale "en_US.utf8".
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".

Data page checksums are disabled.

initdb: error: directory "/var/lib/postgresql/data" exists but is not empty
If you want to create a new database system, either remove or empty
the directory "/var/lib/postgresql/data" or run initdb
with an argument other than "/var/lib/postgresql/data".
Starting installation ...
Validate installation settings ...
Create file system structures ...
Create self-signed certificate database ...
Error: Instance creation failed!  Failed to start DS
The following derivation will be built:
  /gnu/store/5jx2cj780cqs2pp575rckvrx45j9kysy-install-bootloader.scm.drv

building /gnu/store/5jx2cj780cqs2pp575rckvrx45j9kysy-install-bootloader.scm.drv...
guix system: bootloader successfully installed on '(/dev/sda)'
shepherd: Evaluating user expression (and (defined? (quote transient?)) (map (# ?) ?)).
The following derivation will be built:
  /gnu/store/q933nvsqjx2f9zra91jbpjvb9x2yf2sn-upgrade-shepherd-services.scm.drv

building /gnu/store/q933nvsqjx2f9zra91jbpjvb9x2yf2sn-upgrade-shepherd-services.scm.drv...
shepherd: Service host-name has been started.
shepherd: Service user-homes has been started.
shepherd: Service sysctl has been started.
shepherd: Service host-name has been started.
shepherd: Service term-console could not be started.
shepherd: Service postgres-roles has been started.
shepherd: Service directory-server-localhost could not be started.
To complete the upgrade, run 'herd restart SERVICE' to stop,
upgrade, and restart each service that was not automatically restarted.
Run 'herd status' to view the list of services on your system.
--8<---------------cut here---------------end--------------->8---

You see that there is output of tools that run as part of service
activation snippets.  It is not clear which service is responsible for
any particular line of output.

What service produced the line “Error: Instance creation failed!  Failed
to start DS”, for example?  I know it’s the directory-server-localhost
service, because that’s what I’m working on right now, but it’s not
clear from the output.

What do you think of prefixing every line with the name of the service
that is responsible for it?  This way we could probably also
prettify/post-process the output somewhat.

-- 
Ricardo