Cure found for kernel updates

[Matthew Garrett]

Something like this (completely untested) patch ought to do roughly the 
right thing.

diff --git a/grub-core/commands/blscfg.c b/grub-core/commands/blscfg.c
index 4274aca..c9c8fc0 100644
--- a/grub-core/commands/blscfg.c
+++ b/grub-core/commands/blscfg.c
@@ -54,8 +54,9 @@ static int parse_entry (
   char *p;
   grub_file_t f = NULL;
   grub_off_t sz;
-  char *title = NULL, *options = NULL, *clinux = NULL, *initrd = NULL, *src = NULL;
+  char *title = NULL, *options = NULL, *clinux = NULL, *initrd = NULL, *src = NULL, *target = NULL;
   const char *args[2] = { NULL, NULL };
+  int drive = -1, partition;
 
   if (filename[0] == '.')
     return 0;
@@ -113,25 +114,51 @@ static int parse_entry (
 	  if (!initrd)
 	    goto finish;
 	}
+      else if (grub_strncmp (buf, "chainload-disk ", 15) == 0)
+	{
+	  drive = (int) grub_strtoul (buf + 15, 0, 10);
+	  if (grub_errno != GRUB_ERR_NONE)
+	    goto fail;
+	}
+      else if (grub_strncmp (buf, "chainload-partition ", 20) == 0)
+	{
+	  partition = (int) grub_strtoul (buf + 20, 0, 10);
+	  if (grub_errno != GRUB_ERR_NONE)
+	    goto fail;
+	}
 
       grub_free(buf);
     }
 
-  if (!linux)
+  if (!linux && drive < 0)
     {
-      grub_printf ("Skipping file %s with no 'linux' key.", p);
+      grub_printf ("Skipping file %s with no 'linux' or 'chainload-disk' key.",
+		   p);
       goto finish;
     }
 
   args[0] = title ? title : filename;
 
-  src = grub_xasprintf ("load_video\n"
-			"set gfx_payload=keep\n"
-			"insmod gzio\n"
-			GRUB_LINUX_CMD " %s%s%s%s\n"
-			"%s%s%s%s",
-			GRUB_BOOT_DEVICE, clinux, options ? " " : "", options ? options : "",
-			initrd ? GRUB_INITRD_CMD " " : "", initrd ? GRUB_BOOT_DEVICE : "", initrd ? initrd : "", initrd ? "\n" : "");
+  if (drive) {
+    if (partition) {
+      target = grub_xasprintf("chainloader (hd%d,%d)+1", drive, partition);
+    } else {
+      target = grub_xasprintf("chainloader (hd%d)+1", drive);
+    }
+    src = grub_xasprintf ("insmod part_msdos\n"
+			  "insmod chain\n"
+			  "%s\n",
+			  target
+			  );
+  } else {
+    src = grub_xasprintf ("load_video\n"
+			  "set gfx_payload=keep\n"
+			  "insmod gzio\n"
+			  GRUB_LINUX_CMD " %s%s%s%s\n"
+			  "%s%s%s%s",
+			  GRUB_BOOT_DEVICE, clinux, options ? " " : "", options ? options : "",
+			  initrd ? GRUB_INITRD_CMD " " : "", initrd ? GRUB_BOOT_DEVICE : "", initrd ? initrd : "", initrd ? "\n" : "");
+  }
 
   grub_normal_add_menu_entry (1, args, NULL, NULL, "bls", NULL, NULL, src, 0);
 
@@ -142,6 +169,7 @@ finish:
   grub_free (clinux);
   grub_free (initrd);
   grub_free (src);
+  grub_free (target);
 
   if (f)
     grub_file_close (f);

-- 
Matthew Garrett | mjg59 at srcf.ucam.org