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From: "Yoshinori K. Okuji" <okuji@enbug.org>
Organization: enbug.org
To: The development of GRUB 2 <grub-devel@gnu.org>
Date: Sat, 5 Jan 2008 02:22:17 +0100
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Subject: Re: variable hooks & global variables
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On Thursday 03 January 2008 16:05, Robert Millan wrote:
> On Thu, Jan 03, 2008 at 04:03:11PM +0100, Robert Millan wrote:
> > When you set a variable hook (grub_register_variable_hook), this hook
> > isn't preserved after someone (e.g. configfile command) opens a new
> > context (grub_env_context_open), unless the variable has been set as
> > global (grub_env_export).
> >
> > Is this what we want?
> >
> > The only current user of variable hooks is "root" variable, and that hook
> > contains a sanity check that seems to be more suitable for global scope.
> >
> > The color-related variables for which I wanted to add hooks would also
> > like to keep their hooks across contexts.
> >
> > One option is to export these variables, or to modify
> > grub_env_context_open() to preserve hooks as well as exported variables. 
> > I'm more inclined for the latter.
> >
> > Comments?
>
> Erm, ignore the part about global variables.  Exporting them doesn't help:
>
>       for (var = context->prev->vars[i]; var; var = var->next)
>         {
>           if (var->type == GRUB_ENV_VAR_GLOBAL)
>             if (grub_env_set (var->name, var->value) != GRUB_ERR_NONE)
>               {
>                 grub_env_context_close ();
>                 return grub_errno;
>               }
>         }
>
> So, we just preserve hooks ?

Global variables should preserve hooks. This is a bug. Local ones should not. 
If you want to have a variable to be inherited, you must make it global.

Okuji