Re: Please review my Bluetooth run script

[Laurent Bercot <ska-supervision@skarnet.org>]

> We're running an embedded Linux system, so I was trying to keep the
> number of running processes to a minimum. I guess the runsv is fairly
> light?

 Ah, it's good too see that embedded developers use smart supervision
systems and good-quality, small-sized, software. :)
 The runsv process is quite light, you don't need to worry about it.
To be convinced, compile runit statically with the small libc of your
choice, and look at the size of the executables and the memory
footprints.

 Note: if you're not using logging at all, and you need to optimize
as much as you can, you might consider switching to daemontools.
runsv embeds the logging facility, while supervise does not, so I
think supervise should be a bit lighter. But it's a very minor
optimization, and sticking to runit might give you more benefits.


> So are you recommending that I use a Sys-V script to start all the runsv
> services?

 I'm certainly not advocating a SysV scheme. Actually I'm not advocating
any scheme at all. A simple one-time script will do. The SysV stuff
is an overcomplicated way of running one-time scripts. :)


> I currently use UDEV to do an "sv up bluetooth" when the Bluetooth
> device is inserted. I guess I could just as easily do "sv up hcid; sv up
> sdpd; ... ".
> 
> No-one actually calls "sv down" because it's an embedded system with no
> physical user interface, the services are only stopped when the device
> is power cycled, which is fairly common and expected.

 Well, as I understand it, you want to start your Bluetooth daemons as
soon as your embedded thingie is powered: then you don't need to write
any script at all. Just have your Bluetooth service directories, with
appropriate run scripts, in /var/service or wherever runsvdir is run.
 runsvdir will spawn runsv processes, which will automatically start
your daemons (unless you have "down" files in the service directories).

 If you need to send rfcomm commands, perform them in the one-time
initialization (i.e. /etc/runit/1), since rfcomm is a short-lived
program. If you need to send them _after_ the daemons are up, it's
a bit trickier; but you should already have devised a way to
execute a one-time script once the services have been started, just
add your rfcomm lines to that script.

-- 
 Laurent