GPT: add accessor function for disk GUID

In order to read the GPT, modify the partition name strings, and then
write out a new GPT, the disk GUID is needed.  While there is an
existing accessor for the partition UUIDs, there is none yet for the
disk GUID.

Changes since v6: none.

Signed-off-by: Alison Chaiken <alison@peloton-tech.com>

cmd/gpt.c

@@ -398,6 +398,23 @@ static int gpt_verify(struct blk_desc *blk_dev_desc, const char *str_part)
 	return ret;
 }
 
+static int do_disk_guid(struct blk_desc *dev_desc, char * const namestr)
+{
+	int ret;
+	char disk_guid[UUID_STR_LEN + 1];
+
+	ret = get_disk_guid(dev_desc, disk_guid);
+	if (ret < 0)
+		return CMD_RET_FAILURE;
+
+	if (namestr)
+		setenv(namestr, disk_guid);
+	else
+		printf("%s\n", disk_guid);
+
+	return ret;
+}
+
 /**
  * do_gpt(): Perform GPT operations
  *
@@ -436,6 +453,8 @@ static int do_gpt(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 	} else if ((strcmp(argv[1], "verify") == 0)) {
 		ret = gpt_verify(blk_dev_desc, argv[4]);
 		printf("Verify GPT: ");
+	} else if (strcmp(argv[1], "guid") == 0) {
+		ret = do_disk_guid(blk_dev_desc, argv[4]);
 	} else {
 		return CMD_RET_USAGE;
 	}
@@ -458,4 +477,11 @@ U_BOOT_CMD(gpt, CONFIG_SYS_MAXARGS, 1, do_gpt,
 	" Example usage:\n"
 	" gpt write mmc 0 $partitions\n"
 	" gpt verify mmc 0 $partitions\n"
+	" guid <interface> <dev>\n"
+	"    - print disk GUID\n"
+	" guid <interface> <dev> <varname>\n"
+	"    - set environment variable to disk GUID\n"
+	" Example usage:\n"
+	" gpt guid mmc 0\n"
+	" gpt guid mmc 0 varname\n"
 );

disk/part_efi.c

@@ -178,6 +178,37 @@ static void prepare_backup_gpt_header(gpt_header *gpt_h)
  * Public Functions (include/part.h)
  */
 
+/*
+ * UUID is displayed as 32 hexadecimal digits, in 5 groups,
+ * separated by hyphens, in the form 8-4-4-4-12 for a total of 36 characters
+ */
+int get_disk_guid(struct blk_desc * dev_desc, char *guid)
+{
+	ALLOC_CACHE_ALIGN_BUFFER_PAD(gpt_header, gpt_head, 1, dev_desc->blksz);
+	gpt_entry *gpt_pte = NULL;
+	unsigned char *guid_bin;
+
+	/* This function validates AND fills in the GPT header and PTE */
+	if (is_gpt_valid(dev_desc, GPT_PRIMARY_PARTITION_TABLE_LBA,
+			 gpt_head, &gpt_pte) != 1) {
+		printf("%s: *** ERROR: Invalid GPT ***\n", __func__);
+		if (is_gpt_valid(dev_desc, dev_desc->lba - 1,
+				 gpt_head, &gpt_pte) != 1) {
+			printf("%s: *** ERROR: Invalid Backup GPT ***\n",
+			       __func__);
+			return -EINVAL;
+		} else {
+			printf("%s: ***        Using Backup GPT ***\n",
+			       __func__);
+		}
+	}
+
+	guid_bin = gpt_head->disk_guid.b;
+	uuid_bin_to_str(guid_bin, guid, UUID_STR_FORMAT_GUID);
+
+	return 0;
+}
+
 void part_print_efi(struct blk_desc *dev_desc)
 {
 	ALLOC_CACHE_ALIGN_BUFFER_PAD(gpt_header, gpt_head, 1, dev_desc->blksz);

doc/README.gpt

@@ -171,7 +171,8 @@ To restore GUID partition table one needs to:
    The fields 'uuid' and 'uuid_disk' are optional if CONFIG_RANDOM_UUID is
    enabled. A random uuid will be used if omitted or they point to an empty/
    non-existent environment variable. The environment variable will be set to
-   the generated UUID.
+   the generated UUID.  The 'gpt guid' command reads the current value of the
+   uuid_disk from the GPT.
 
    The field 'bootable' is optional, it is used to mark the GPT partition
    bootable (set attribute flags "Legacy BIOS bootable").

include/part.h

@@ -372,6 +372,21 @@ int gpt_verify_headers(struct blk_desc *dev_desc, gpt_header *gpt_head,
 int gpt_verify_partitions(struct blk_desc *dev_desc,
 			  disk_partition_t *partitions, int parts,
 			  gpt_header *gpt_head, gpt_entry **gpt_pte);
+
+
+/**
+ * get_disk_guid() - Function to read the GUID string from a device's GPT
+ *
+ * This function reads the GUID string from a block device whose descriptor
+ * is provided.
+ *
+ * @param dev_desc - block device descriptor
+ * @param guid - pre-allocated string in which to return the GUID
+ *
+ * @return - '0' on success, otherwise error
+ */
+int get_disk_guid(struct blk_desc *dev_desc, char *guid);
+
 #endif
 
 #if CONFIG_IS_ENABLED(DOS_PARTITION)