Adding a 'setup' phase to service startup?

[Lars Kellogg-Stedman <lars@oddbit.com>]

I was mulling over service dependencies yesterday, and I wonder if it would
make sense to add a "setup" phase to runsv's service startup sequence.
This would allow, for example, svwaitup to block while a service performed
one time initialization.

Here I'm thinking particularly of long-running setup actions, such as
database initialization or something.  The current solution -- waiting for
a number of seconds and then crossing our fingers -- doesn't provide the
level of control that runit provides in other areas.

This would make the start sequence look like this:

  IF file "setup" exists THEN
    SET STATE TO S_SETUP
    RUN file "setup"
  END IF

  SET STATE TO S_RUN
  RUN file "run"

  IF file "finish" exists THEN
    SET STATE TO S_FINISH
    RUN file "finish"
  END IF

svwaitup() would block if a service was in the "setup" phase.  This should
require only minor changes to runit -- introduce "runsv" to the "setup"
script, and modify svwaitup, svwaitdown, and runsvstat to understand a new
state value in the status file.

-- Lars

-- 
Lars Kellogg-Stedman <lars@oddbit.com>