[PATCH 3/3] grub-mkrescue: Search by file UUID file rather than partition UUID for EFI boot

[Pete Batard]

The final piece we need to add file system transposition support for UEFI
is to ensure that we can locate the boot media regardless of how the boot
partition was instantiated. Especially, we do not want to be reliant on
brittle partition UUIDs, as these only work if a boot media is duplicated at
the block level and not at the file system level.

To accomplish this for EFI boot, we now create a UUID file in a .disk/
directory, that we can then search for.

Signed-off-by: Pete Batard <pete@akeo.ie>
---
 util/grub-mkrescue.c | 47 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 39 insertions(+), 8 deletions(-)

diff --git a/util/grub-mkrescue.c b/util/grub-mkrescue.c
index 4596f0ea7..b7a387d8b 100644
--- a/util/grub-mkrescue.c
+++ b/util/grub-mkrescue.c
@@ -261,7 +261,26 @@ make_image_abs (enum grub_install_plat plat,
   load_cfg = grub_util_make_temporary_file ();
 
   load_cfg_f = grub_util_fopen (load_cfg, "wb");
-  fprintf (load_cfg_f, "search --fs-uuid --set=root %s\n", iso_uuid);
+  /* 
+   * A UEFI bootable media should support file system transposition (e.g. 
extracting
+   * an ISO9660 content to a FAT32 media that was formatted by the user). 
Therefore,
+   * for EFI platforms, we search for a specific UUID file rather than a 
partition UUID.
+   */
+  switch (plat)
+    {
+      case GRUB_INSTALL_PLATFORM_I386_EFI:
+      case GRUB_INSTALL_PLATFORM_X86_64_EFI:
+      case GRUB_INSTALL_PLATFORM_IA64_EFI:
+      case GRUB_INSTALL_PLATFORM_ARM_EFI:
+      case GRUB_INSTALL_PLATFORM_ARM64_EFI:
+      case GRUB_INSTALL_PLATFORM_RISCV32_EFI:
+      case GRUB_INSTALL_PLATFORM_RISCV64_EFI:
+       fprintf (load_cfg_f, "search --set=root --file /.disk/%s.uuid\n", 
iso_uuid);
+       break;
+      default:
+       fprintf (load_cfg_f, "search --fs-uuid --set=root %s\n", iso_uuid);
+       break;
+    }
   fprintf (load_cfg_f, "set prefix=(${root})/boot/grub\n");
 
   write_part (load_cfg_f, source_dirs[plat]);
@@ -745,10 +764,11 @@ main (int argc, char *argv[])
       || source_dirs[GRUB_INSTALL_PLATFORM_RISCV32_EFI]
       || source_dirs[GRUB_INSTALL_PLATFORM_RISCV64_EFI])
     {
+      FILE *f;
       char *efidir_efi = grub_util_path_concat (2, iso9660_dir, "efi");
       char *efidir_efi_boot = grub_util_path_concat (3, iso9660_dir, "efi", 
"boot");
       char *imgname, *img32, *img64, *img_mac = NULL;
-      char *efiimgfat;
+      char *efiimgfat, *iso_uuid_file, *diskdir, *diskdir_uuid;
       grub_install_mkdir_p (efidir_efi_boot);
 
       grub_install_push_module ("part_gpt");
@@ -757,36 +777,47 @@ main (int argc, char *argv[])
       /* Many modern UEFI systems also have native support for NTFS */
       grub_install_push_module ("ntfs");
 
+      /* Create a '.disk/<TIMEBASED_UUID>.uuid' file that can be used to 
locate the boot media. */
+      diskdir = grub_util_path_concat (2, iso9660_dir, ".disk");
+      grub_install_mkdir_p (diskdir);
+      iso_uuid_file = xasprintf ("%s.uuid", iso_uuid);
+      diskdir_uuid = grub_util_path_concat (2, diskdir, iso_uuid_file);
+      f = grub_util_fopen (diskdir_uuid, "wb");
+      fclose (f);
+      free (iso_uuid_file);
+      free (diskdir_uuid);
+      free (diskdir);
+
       imgname = grub_util_path_concat (2, efidir_efi_boot, "bootia64.efi");
       make_image_fwdisk_abs (GRUB_INSTALL_PLATFORM_IA64_EFI, "ia64-efi", 
imgname);
       free (imgname);
 
       grub_install_push_module ("part_apple");
       img64 = grub_util_path_concat (2, efidir_efi_boot, "bootx64.efi");
-      make_image_fwdisk_abs (GRUB_INSTALL_PLATFORM_X86_64_EFI, "x86_64-efi", 
img64);
+      make_image_abs (GRUB_INSTALL_PLATFORM_X86_64_EFI, "x86_64-efi", img64);
       grub_install_pop_module ();
 
       grub_install_push_module ("part_apple");
       img32 = grub_util_path_concat (2, efidir_efi_boot, "bootia32.efi");
-      make_image_fwdisk_abs (GRUB_INSTALL_PLATFORM_I386_EFI, "i386-efi", 
img32);
+      make_image_abs (GRUB_INSTALL_PLATFORM_I386_EFI, "i386-efi", img32);
       grub_install_pop_module ();
 
       imgname = grub_util_path_concat (2, efidir_efi_boot, "bootarm.efi");
-      make_image_fwdisk_abs (GRUB_INSTALL_PLATFORM_ARM_EFI, "arm-efi", 
imgname);
+      make_image_abs (GRUB_INSTALL_PLATFORM_ARM_EFI, "arm-efi", imgname);
       free (imgname);
 
       imgname = grub_util_path_concat (2, efidir_efi_boot, "bootaa64.efi");
-      make_image_fwdisk_abs (GRUB_INSTALL_PLATFORM_ARM64_EFI, "arm64-efi",
+      make_image_abs (GRUB_INSTALL_PLATFORM_ARM64_EFI, "arm64-efi",
                             imgname);
       free (imgname);
 
       imgname = grub_util_path_concat (2, efidir_efi_boot, "bootriscv32.efi");
-      make_image_fwdisk_abs (GRUB_INSTALL_PLATFORM_RISCV32_EFI, "riscv32-efi",
+      make_image_abs (GRUB_INSTALL_PLATFORM_RISCV32_EFI, "riscv32-efi",
                             imgname);
       free (imgname);
 
       imgname = grub_util_path_concat (2, efidir_efi_boot, "bootriscv64.efi");
-      make_image_fwdisk_abs (GRUB_INSTALL_PLATFORM_RISCV64_EFI, "riscv64-efi",
+      make_image_abs (GRUB_INSTALL_PLATFORM_RISCV64_EFI, "riscv64-efi",
                             imgname);
       free (imgname);
 
-- 
2.36.0.windows.1