[GRUB PARTUUID PATCH V4 2/3] Add PARTUUID detection support to grub-probe

[Nicholas Vinson]

Add PARTUUID detection support grub-probe for MBR and GPT partition
schemes.  The Linux kernel supports mounting the root filesystem by
Linux device name or by the Partition [GU]UID.  GRUB's mkconfig,
however, currently only supports specifing the rootfs in the kernel
command-line by Linux device name unless an initramfs is also present.
When an initramfs is present GRUB's mkconfig will set the kernel's root
parameter value to either the Linux device name or to the filesystem
[GU]UID.

Therefore, the only way to protect a Linux system from failing to boot
when its Linux storage device names change is to either manually edit
grub.cfg or /etc/default/grub and append root=PARTUUID=xxx to the
command-line or create an initramfs that understands how to mount
devices by filesystem [G]UID and let grub-mkconfig pass the filesystem
[GU]UID to the initramfs.

The goal of this patch set is to enable root=PARTUUID=xxx support in
grub-mkconfig, so that users don't have to manually edit
/etc/default/grub or grub.cfg, or create an initramfs for the sole
purpose of having a robust bootloader configuration for Linux.
---
 util/grub-probe.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/util/grub-probe.c b/util/grub-probe.c
index 21cb80fbe..3656e32e8 100644
--- a/util/grub-probe.c
+++ b/util/grub-probe.c
@@ -28,6 +28,7 @@
 #include <grub/partition.h>
 #include <grub/msdos_partition.h>
 #include <grub/gpt_partition.h>
+#include <grub/i386/pc/boot.h>
 #include <grub/emu/hostdisk.h>
 #include <grub/emu/getroot.h>
 #include <grub/term.h>
@@ -62,6 +63,7 @@ enum {
   PRINT_DRIVE,
   PRINT_DEVICE,
   PRINT_PARTMAP,
+  PRINT_PARTUUID,
   PRINT_ABSTRACTION,
   PRINT_CRYPTODISK_UUID,
   PRINT_HINT_STR,
@@ -85,6 +87,7 @@ static const char *targets[] =
     [PRINT_DRIVE]              = "drive",
     [PRINT_DEVICE]             = "device",
     [PRINT_PARTMAP]            = "partmap",
+    [PRINT_PARTUUID]           = "partuuid",
     [PRINT_ABSTRACTION]        = "abstraction",
     [PRINT_CRYPTODISK_UUID]    = "cryptodisk_uuid",
     [PRINT_HINT_STR]           = "hints_string",
@@ -182,6 +185,48 @@ probe_partmap (grub_disk_t disk, char delim)
 }
 
 static void
+probe_partuuid (grub_disk_t disk, char delim)
+{
+  /*
+   * Nested partitions not supported for now.
+   * Non-nested partitions must have disk->partition->parent == NULL
+   */
+  if (disk->partition && disk->partition->parent == NULL)
+    {
+      if (strcmp(disk->partition->partmap->name, "msdos") == 0)
+       {
+           /*
+            * The partition GUID for MSDOS is the partition number (starting
+            * with 1) prepended with the NT disk signature.
+            */
+            grub_uint32_t nt_disk_sig;
+           grub_partition_t p = disk->partition;
+           disk->partition = p->parent;
+
+           if (grub_disk_read (disk, 0, GRUB_BOOT_MACHINE_WINDOWS_NT_MAGIC,
+                               sizeof(nt_disk_sig), &nt_disk_sig) == 0)
+             {
+               grub_printf ("%08x-%02x",
+                            grub_le_to_cpu32(nt_disk_sig), 1 + p->number);
+             }
+           disk->partition = p;
+       }
+      else if (strcmp(disk->partition->partmap->name, "gpt") == 0)
+       {
+         grub_partition_t p = disk->partition;
+         struct grub_gpt_partentry gptdata;
+
+         disk->partition = p->parent;
+
+         if (grub_disk_read (disk, p->offset, p->index,
+                             sizeof(gptdata), &gptdata) == 0)
+           print_gpt_guid(gptdata.guid);
+         disk->partition = p;
+       }
+    }
+}
+
+static void
 probe_cryptodisk_uuid (grub_disk_t disk, char delim)
 {
   grub_disk_memberlist_t list = NULL, tmp;
@@ -635,6 +680,12 @@ probe (const char *path, char **device_names, char delim)
        /* Check if dev->disk itself is contained in a partmap.  */
        probe_partmap (dev->disk, delim);
 
+      else if (print == PRINT_PARTUUID)
+       {
+         probe_partuuid (dev->disk, delim);
+         putchar (delim);
+       }
+
       else if (print == PRINT_MSDOS_PARTTYPE)
        {
          if (dev->disk->partition
-- 
2.13.0