[PATCH] savedefault

[Carlo Contavalli]

Hi!
  In the attachment, you'll find a small and dumb patch for 
grub that:

        - allows usage of savedefault both from the 
          os command line and the boot time one
        - allows to specify which default to save 
        - adds the command showdefault 

  The purpose of the changes is to allow smoother 
home-compiled kernel updates on remotely located
servers.
  For example, using the provided patch and
``default saved'' in menu.lst, after installing
a new kernel, I could: 

  1) add a new entry 0 in menu.lst without removing the 
     old ones, inserting a ``savedefault 1'' and 
     giving ``panic=10'' as a parameter to 
     the linux kernel

  3) run grub from the command line (either at 
     boot time or from the grub shell) and give the
     command ``savedefault 0''

  4) reboot the system

During the first boot, the default entry 0 is chosen
since it was saved as the default one.
Once the entry is loaded, the default is set to 1 thanks
to ``savedefault 1''.
If the kernel panics, the parameter panic=10 will make
the system reboot in 10 seconds. During the following
boot up, grub will run entry 1 as default instead of 
entry 0.
  When the system boots up, an init script could
easily detect if the new kernel or the old one had
been loaded and do something smart about that. In
case of success, it could, for example, run
``savedefault 0'' to set again the new kernel as
default and remove ``savedefault 1'' from the menu.lst
and finally remove the old kernel. 

  Ok, the patch was made against grub 0.93 + cvs
20030224 as provided in the corresponding debian
package + the patch for the el torito hd boot 
images. I wrote it since I needed to update the
kernel on some machines without being there.
It's just a one morning effort, so don't blame
me too much. I just thought it could be useful to 
others. It should apply cleanly on the vanilla
version of grub, beside maybe a reject in 
stage2/builtins.c due to patch not being able
to figure out where to add &builtin_showdefault 
in builtin_table[].
  A couple defines avoid conflicts with the el
torito patch due to missing ERR_CANT_SEEK and
COMPAT_VERSION being a char instead of a short.
They really should be removed, and a good sed
should make it.

  Please consider that I'm not subscribed
to the mailing list and that I don't follow
closely the development of grub, so please 
carbon copy any comment to my private email 
address and forgive me if the issue had already 
been discussed in the mailing list..

Bye,
Carlo

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Perl itself is usually pretty good about telling you what you shouldn't
do. :-)
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grub.patch.diff
Description: Text document