-------- Original-Nachricht -------- Betreff: Re: [arch-dev-public] [PATCH] Implement a hook-system that allows to add custom code to the initscripts at certain places Datum: Wed, 26 Aug 2009 15:10:16 +0200 Von: Michael Towers <larch42@googlemail.com> An: Thomas Bächler <thomas@archlinux.org> Referenzen: <4A93C509.7060505@archlinux.org> <4A93C694.3030401@archlinux.org> <ed5b1830908260446o4cd75196s617baf1a3dd68db4@mail.gmail.com> <4A95255D.2080507@archlinux.org> 2009/8/26 Thomas Bächler <thomas@archlinux.org>:

Full-quoting, as your mail didn't go to the list.

Michael Towers schrieb:

...

2009/8/25 Thomas Bächler <thomas@archlinux.org>:

...

Thomas Bächler schrieb:

...

A function add_hook can be called from functions.d to register a hook function. The existing hooks are based on suggestions from Michael Towers (larch) and on the implementation of initscripts-extras-fbsplash which currently uses the strings passed to stat_busy and stat_done for this. More hooks can be added if requested.

Forgot to mention this in the commit and the first mail: the hook function names should be prefixed by something to make them unique, for example:

add_hook premount larch_premount

If larch would decide to add a "premount" hook.

I've had a look at this now and find it basically a pretty good idea, though I think I slightly prefer my suggestion.

Hmm, your suggestion required an extra file per hook and wouldn't allow several parties to register code for the same hook. That's what I didn't like.

...

This just seems a little too complicated, but I have a couple of ideas for simplifying it a bit. Mainly I'm not so sure about passing the script name as argument and having hooks with the same name (e.g. 'start') in several rc. files. That means that if I write a hook function for 'start' I must always test that the call came from the correct rc. file.

Correct. The idea came up because if I have a "prekillall" hook, users like fbsplash would want to hook up code regardless of whether it is caled from rc.shutdown or rc.single, while other users would only want to use it from rc.shutdown. This was part of my first approach.

With the new approach, I could have a hook shutdown_prekillall and single_prekillall and just register the same function for it:

add_hook single_prekillall my_prekillall add_hook shutdown_prekillall my_prekillall

So this is obsolete now, and I agree that renaming the hooks to be unique is a better idea. If I don't receive a patch for that until tonight, I will do it then.

...

Wouldn't it be simpler to give each hook a unique name, even if it has to be something like 'start_shutdown'?

I will use the convention $FILE_$HOOKTYPE if that is alright, like "sysinit_start" or "shutdown_poweroff".

...

That would be nearly the same as what you are suggesting, but the hook functions would not have to test the argument.

I also have a further suggestion for simplification - the predeclaration of the hook names in the 'functions' file:

for hook in start end udevlaunched udevsettled premount prekillall postkillall poweroff; do hook_funcs["${hook}"]="" done

is not necessary. Bash arrays return empty strings for undefined indexes too. This has the great advantage that when a new hook is added you wouldn't have to edit the 'functions' file.

I still would have to add a comment in 'functions', but I agree.

...

Apart from that it seems quite attractive, if you are determined to keep it all as scripts in functions.d.

Yes, I don't want to add extra directories, functions.d can serve several purposes quite fine. And if you like, your hooks can just be wrappers that will call scripts from other places.

Anyway, I'm glad that this is an approach you are willing to work with, and I hope fbsplash will also adopt this instead of parting $1 in stat_busy and stat_done.

Can you give suggestions regarding the hook names (I still find some of them sound weird) and comment on whether more hooks are needed, or some of them are badly placed?

...

Regards, mt

It sounds like my wishes will be well satisfied now! As to the names, it's not something that seems terribly important to me. I try to comment my code anyway and so it wouldn't even be a disaster if they had names like x23_ooo_aaah (ok, I'm exaggerating, they should probably make some sort of sense). I also can't say much about their placement in general or suggest further places as I have only really thought about the places the current larch design would use, and you already have those. I guess you got the others from fbsplash. Maybe at the beginning there shouldn't be too many - it would be easier to add a new one than to move an old one (which somebody might already be using). Maybe briefly the reasons I requested this for larch. In a live system it is helpful to have a bit of flexibility in the way the system is started, the root filesystem is mostly aufs (etc.) and what should appear in /etc/mtab is probably not the same as in a non-live system, also what should get mounted or entered in fstab might well change from boot to boot (from machine to machine). There are other points at which this can be done, but via a hook in rc.sysinit seems cleaner to me. As to rc.shutdown, the main need in larch is caused by session saving, which is probably cleanest/safest when carried out towards the end of the shutdown process. With CDs there is also the question of ejecting the device, which must also happen right at the end. Up to now I have used modified rc.sysinit and rc.shutdown scripts to achieve this, which means editing them every time initscripts is updated - rather annoying. Thanks for your interest and work, mt