[Splashy-devel] about splashy-init

[Jacobo221]

hi Goshawk,

This is Jacobo221. I read from the #splashy at freenode IRC log that you are
interested in knowing how splashy-init does its "magic" (when it works
hehe).

I am writing a quick but deep explanation for you. If there is any part
which you'd like to know more about, i'll be pleased to write you about it.

----

First, notice that the README file in the scripts/ directory explains all
the details about configuring splashy-init.

splashy-init is a normal service that will be run by rc or rcS during
boot/reboot/shutdown/runlevel-switch.

modes other than "start" and "stop" won't be explaied here since they are
pretty easy and non-tricky, so nothing to explain really.

Of course, it is LSB complaint (mostly, though in some aspects it cannot be
made compatible due to some LSB restrictions which cannot be applied here).
It will use LSB functions if LSB is installed. if it is not, it will emulate
the LSB functions with builtin functions which provide similar (if not the
same) functionality. This is to avoid adding LSB as a dependency to splashy.

When splashy-init starts it tries to determine what runlevel it is going to
and what runlevel it is on, if it is being run as an init (rc/rcS) script or
by hand by the user, if it is supposed to start or stop splashy, etc. it set
s some variables according to these values. It will refuse to start if
runlevel is 1 or if another splashy-init is running.

then it will check all the configuration settings. if any setting is
incorrect, it will stop. unset settings wil be set to their default values.

inmediately after it will try to start splashy. this is only an attempt. if
this attempt fails, splashy-init will go on normaly as if it hadn't tried.
this is because at boot time, splashy-init might be run before /proc or /dev
are mounted. In this case splashy could not be run because /dev/fb0 is not
accessible. so, in case it can, it will start splashy inmediately, but if it
cannot, it will try again later.

next it will call itself (splashy-init) to background itself. that is, it
will enter daemon mode. the caller splashy-init will exit so that the rc/rcS
scripts can keep calling the rest of the services.

the backgrounded dameon splashy-init will start. first it will make
absolutely sure that it hsan't been called directly by a user running
"splashy-init daemon" explicitly. In other words, it makes sure that it has
been called from another splashy-init process. if it wasn't, it will exit.

next it will check if splashy was successfully started from the caller
splashy-init. if it wasn't, it will try to start it now. before starting
splashy it will check that the console and the framebuffer devices are
available and that the proc filesystem is mounted. if any of them isn't, it
will wait until it is. It will wait indefinitely for proc since it is
supposed to be mounted on any linux system, while for the fb and the console
devices it will timeout if they take too long to be available. if it
timesout, it will exit.

after starting splashy it will explicitly check that it has been
successfully started since that is the key part.

next it will initialize progress variables (only if the installed theme has
a progress bar) and set up the signals trapping.

up to now all this is done in few deciseconds. now comes the main loop. this
is very tricky so i'll just sum it up:

splashy-init will now check the runlevel it is going to and get the list of
scriptnames that will be executed. it will generate an index out of the
list.

from now on it will now go checking the running processes' complete command
names to find init scripts. when it finds one, it will check the index and
see in what step of the runlevel change that script is being called. it wil
then update the progress in splashy through the fifo (actually, through
splashy_update). if the progress number is the same as the last sent, it
will not call splashy_update. of course, all the progress stuff is skipped
if the isntalled theme doesn't have a progress bar. when it detects that the
last script is being executed it will complete the bar and exit.

some init scirpts are executed when splashy should have already been
completed. for example, any service running after gdm or kdm. in such case,
when splashy-init sees that a service is being run and that it it is run
after gdm/kdm/etc it will also complete the bar and exit.

if at any moment it cannot detect the running service, it will determine if
that is because init has stopped running rc/rcS. if it has, it will complete
the bar and exit. otherwise it will keep looping.

when completing the bar, unless otherwise set in the settings, it will
detect if X is running and, if so, in which console and switch there.

----

as you can see, i avoided the details, but went through a complete
description with the code in front of my eyes to follow up. i hope this can
help you to understand how it works.

Anyway, the code is quite commented explaining almost every single line so
it should be easy to go into details seeing the code now that you should get
the general idea quite well (if i did well in this task, that is).

i'm CC-ing this to splashy-devel so anyone can check this in the future.

greets!
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