util/grub-mkrescue: Search by file UUID rather than partition UUID for EFI boot

The final piece needed to add UEFI file system transposition support is to
ensure the boot media can be located 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 can then be searched for.

Note: The switch from make_image_fwdisk_abs() to make_image_abs() is
needed in order to use the search functionality.

Signed-off-by: Pete Batard <pete@akeo.ie>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

diff --git a/util/grub-mkrescue.c b/util/grub-mkrescue.c
index b9d16f5add02305437b9e6725e5f0dbc78ec533d..1e0e40ca6ab6e0eb0fe84d6db9249d7a3ef293fa 100644 (file)
--- 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 ISO 9660 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 --set=root --fs-uuid %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");
@@ -757,37 +777,45 @@ 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",
-                            imgname);
+      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",
-                            imgname);
+      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",
-                            imgname);
+      make_image_abs (GRUB_INSTALL_PLATFORM_RISCV64_EFI, "riscv64-efi", imgname);
       free (imgname);
 
       if (source_dirs[GRUB_INSTALL_PLATFORM_I386_EFI])