Re: user-defined hooks

[Hollis Blanchard <hollis@penguinppc.org>]

On Thu, 2006-11-30 at 20:50 +0100, Marco Gerards wrote:
> Actually, what I would prefer is something hooks.  It would be nice if
> the C code in GRUB and perhaps also scripts can be hooked anywhere.
> We have to be very careful about this, so perhaps limit the sets of
> commands that can be used this way.  But I think it will make GRUB
> more flexible while it is not too much effort.

I like this idea.

> I am thinking of the following functions:
> 
> One to install a hook:
> grub_err_t grub_hook_register (const char *name, (*hook) (...));
> 
> To trigger the hook (for example, when the user types something,
> selects another menu entry, etc.
> void grub_hook_call (const char *name, ...);
> 
> How to pass arguments to functions and to scripts is something that we
> have to think about.  For example, scripting functions have to get
> strings, while in other cases we just want to deal with regular
> function calls.  Perhaps a printf-like mechanism can help us with
> this.

I do not think it's important that we be able to hook C functions
directly. In other words, the argument passed to --function (below)
should be a script command (or script function), and not a C function
name.

> In that case your problem can be solved by using:
> 
> function handlemenu {
>   beep depending on menuentry selected, the index is passed to this function
> }
> 
> hook --install --hook=select-menu-entry --function=handlemenu

Defining the set of useful hooks, the arguments passed to each, and
documenting them will be critical. Also, just like with commands, once
we implement a hook we can't remove or change it without breaking config
files.

-Hollis