Hi all!
We're interested in implementing a small feature that would drop into
the grub menu (same as when we press shift or f4) if some new EFI
variable is set by the firmware. The motivation here is to enable
firmware vendors to add menu entries that will set this new EFI
variable before booting into the device with GRUB, enabling another
method through which we can access the grub menu on systems where it
is hidden / skipped by default.
I have not previously done any upstream grub development, so I'm
interested in hearing whether this is something the grub team would
consider, or if there are any technical concerns.
My thought is that this could be implemented within normal/menu.c if
you'd be willing to add EFI-specific code there, perhaps along these
lines (just an example, haven't been able to test yet since no
firmware implements this feature):
diff --git a/grub-core/normal/menu.c b/grub-core/normal/menu.c
index b946c834d..7f46d7514 100644
--- a/grub-core/normal/menu.c
+++ b/grub-core/normal/menu.c
@@ -33,6 +33,9 @@
#include <grub/gfxterm.h>
#include <grub/dl.h>
#include <grub/safemath.h>
+#ifdef GRUB_MACHINE_EFI
+#include <grub/efi/efi.h>
+#endif
/* Time to delay after displaying an error message about a default/fallback
entry failing to boot. */
@@ -615,6 +618,14 @@ run_menu (grub_menu_t menu, int nested, int
*auto_boot, int *notify_boot)
/* Enter interruptible sleep until Escape or a menu hotkey is pressed,
or the timeout expires. */
saved_time = grub_get_time_ms ();
+#ifdef GRUB_MACHINE_EFI
+ static grub_guid_t efi_variable_guid = GRUB_EFI_GLOBAL_VARIABLE_GUID;
+ grub_size_t size = 0;
+ grub_efi_status_t status;
+ grub_uint8_t *enter_grub_menu = NULL;
+ status = grub_efi_get_variable ("EnterGrubMenu", &efi_variable_guid,
+ &size, (void **) &enter_grub_menu);
+#endif
while (1)
{
int key;
@@ -632,6 +643,14 @@ run_menu (grub_menu_t menu, int nested, int
*auto_boot, int *notify_boot)
break;
}
+#ifdef GRUB_MACHINE_EFI
+ if (enter_grub_menu)
+ {
+ timeout = -1;
+ break;
+ }
+#endif
+
if (timeout > 0 && has_second_elapsed (&saved_time))
{
timeout--;
--
2.43.0
Thanks in advance for your comments,
--
Mitchell Augustin
Software Engineer - Ubuntu Partner Engineering
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