[U-Boot] [PATCH v5 3/3] rename GPT partitions to detect boot failure

alison at peloton-tech.com alison at peloton-tech.com
Sat Jun 10 05:35:17 UTC 2017


From: Alison Chaiken <alison at she-devel.com>

This patch provides support in u-boot for renaming GPT
partitions.  The renaming is accomplished via a new 'gpt flip'
command.

The concept for the bootloader state machine is the following:

-- u-boot renames ‘primary’ partitions as ‘candidate’ and tries
   to boot them.
-- Linux, at boot, will rename ‘candidate’ partitions as
   ‘primary’.
-- If u-boot sees a ‘candidate’ partition after a boot attempt,
   it tries to boot the ‘backup’ partition.

Rewriting the partition table has the side-effect that all partitions
end up with "msftdata" flag set.  The reason is that partition type
PARTITION_BASIC_DATA_GUID is hard-coded in the gpt_fill_pte()
function.  This does not appear to cause any harm.

Changes since v4:
-- Changed the erroneous '17' values in calc_parts_list_len() to
   match the definition of struct disk_partition in part.h.
-- Modified do_gpt() so that the 'gpt flip' command prints
   "success!" or "error!" on exit.

Signed-off-by: Alison Chaiken <alison at peloton-tech.com>
---
 cmd/Kconfig    |   7 +++
 cmd/gpt.c      | 190 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 doc/README.gpt |  13 ++++
 3 files changed, 206 insertions(+), 4 deletions(-)

diff --git a/cmd/Kconfig b/cmd/Kconfig
index 270cff6..880ca97 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -593,6 +593,13 @@ config CMD_GPT
 	  Enable the 'gpt' command to ready and write GPT style partition
 	  tables.
 
+config CMD_GPT_FLIP
+	bool "GPT flip-partitions command"
+	depends on CMD_GPT
+	help
+	  Enables the 'gpt' command to write modified GPT partition
+	  tables via the 'gpt flip' command.
+
 config CMD_ARMFLASH
 	#depends on FLASH_CFI_DRIVER
 	bool "armflash"
diff --git a/cmd/gpt.c b/cmd/gpt.c
index 669031f8..ad7c7ec 100644
--- a/cmd/gpt.c
+++ b/cmd/gpt.c
@@ -20,6 +20,7 @@
 #include <div64.h>
 #include <memalign.h>
 #include <linux/compat.h>
+#include <linux/sizes.h>
 
 static LIST_HEAD(disk_partitions);
 
@@ -194,16 +195,33 @@ static struct disk_part *allocate_disk_part(disk_partition_t *info, int partnum)
 	return newpart;
 }
 
+static void prettyprint_part_size(char *sizestr, unsigned long partsize,
+				  unsigned long blksize)
+{
+	unsigned long long partbytes;
+	unsigned long partmegabytes;
+
+	partbytes = partsize * blksize;
+	partmegabytes = lldiv(partbytes, SZ_1M);
+	snprintf(sizestr, 16, "%luMiB", partmegabytes);
+}
+
 static void print_gpt_info(void)
 {
 	struct list_head *pos;
 	struct disk_part *curr;
+	char partstartstr[16];
+	char partsizestr[16];
 
 	list_for_each(pos, &disk_partitions) {
 		curr = list_entry(pos, struct disk_part, list);
+		prettyprint_part_size(partstartstr, (unsigned long)curr->gpt_part_info.start,
+				      (unsigned long) curr->gpt_part_info.blksz);
+		prettyprint_part_size(partsizestr, (unsigned long)curr->gpt_part_info.size,
+				      (unsigned long) curr->gpt_part_info.blksz);
+
 		printf("Partition %d:\n", curr->partnum);
-		printf("1st block %x, size %x\n", (unsigned)curr->gpt_part_info.start,
-		       (unsigned)curr->gpt_part_info.size);
+		printf("Start %s, size %s\n", partstartstr, partsizestr);
 		printf("Block size %lu, name %s\n", curr->gpt_part_info.blksz,
 		       curr->gpt_part_info.name);
 		printf("Type %s, bootable %d\n", curr->gpt_part_info.type,
@@ -215,6 +233,74 @@ static void print_gpt_info(void)
 	}
 }
 
+#ifdef CONFIG_CMD_GPT_FLIP
+static int calc_parts_list_len(int numparts)
+{
+	int partlistlen = UUID_STR_LEN + 1 + strlen("uuid_disk=");
+	/* for the comma */
+	partlistlen++;
+
+	/* per-partition additions; numparts starts at 1, so this should be correct */
+	partlistlen += numparts * (strlen("name=,") + PART_NAME_LEN + 1);
+	/* see part.h for definition of struct disk_partition */
+	partlistlen += numparts * (strlen("start=MiB,") + sizeof(lbaint_t) + 1);
+	partlistlen += numparts * (strlen("size=MiB,") + sizeof(lbaint_t) + 1);
+	partlistlen += numparts * (strlen("uuid=;") + UUID_STR_LEN + 1);
+	/* for the terminating null */
+	partlistlen++;
+	debug("Length of partitions_list is %d for %d partitions\n", partlistlen,
+	       numparts);
+	return partlistlen;
+}
+
+/*
+ * create the string that upstream 'gpt write' command will accept as an
+ * argument
+ *
+ * From doc/README.gpt, Format of partitions layout:
+ *    "uuid_disk=...;name=u-boot,size=60MiB,uuid=...;
+ *	name=kernel,size=60MiB,uuid=...;"
+ * The fields 'name' and 'size' are mandatory for every partition.
+ * The field 'start' is optional. The fields 'uuid' and 'uuid_disk'
+ * are optional if CONFIG_RANDOM_UUID is enabled.
+ */
+static int create_gpt_partitions_list(int numparts, const char *guid, char *partitions_list)
+{
+	struct list_head *pos;
+	struct disk_part *curr;
+	char partstr[PART_NAME_LEN + 1];
+
+	if (!partitions_list)
+		return -1;
+
+	strcpy(partitions_list, "uuid_disk=");
+	strncat(partitions_list, guid, UUID_STR_LEN + 1);
+	strcat(partitions_list, ";");
+
+	list_for_each(pos, &disk_partitions) {
+		curr = list_entry(pos, struct disk_part, list);
+		strcat(partitions_list, "name=");
+		strncat(partitions_list, (const char *)curr->gpt_part_info.name, PART_NAME_LEN + 1);
+		strcat(partitions_list, ",start=");
+		prettyprint_part_size(partstr, (unsigned long)curr->gpt_part_info.start,
+				      (unsigned long) curr->gpt_part_info.blksz);
+		/* one extra byte for NULL */
+		strncat(partitions_list, partstr, PART_NAME_LEN + 1);
+		strcat(partitions_list, ",size=");
+		/* lbaint_t is unsigned long, per include/ide.h */
+		prettyprint_part_size(partstr, (unsigned long)curr->gpt_part_info.size,
+				      (unsigned long) curr->gpt_part_info.blksz);
+		strncat(partitions_list, partstr, PART_NAME_LEN + 1);
+
+		strcat(partitions_list, ",uuid=");
+		strncat(partitions_list, (const char *)curr->gpt_part_info.uuid,
+			UUID_STR_LEN + 1);
+		strcat(partitions_list, ";");
+	}
+	return 0;
+}
+#endif
+
 /*
  * read partition info into disk_partitions list where
  * it can be printed or modified
@@ -226,8 +312,11 @@ static int get_gpt_info(struct blk_desc *dev_desc)
 	disk_partition_t info;
 	struct disk_part *new_disk_part;
 
-	if (disk_partitions.next == NULL)
-		INIT_LIST_HEAD(&disk_partitions);
+	/*
+	 * Always re-read partition info from device, in case
+	 * it has changed
+	 */
+	INIT_LIST_HEAD(&disk_partitions);
 
 	for (p = 1; p <= MAX_SEARCH_PARTITIONS; p++) {
 		ret = part_get_info(dev_desc, p, &info);
@@ -302,6 +391,8 @@ static int set_gpt_info(struct blk_desc *dev_desc,
 		return -1;
 
 	str = strdup(str_part);
+	if (str == NULL)
+		return -ENOMEM;
 
 	/* extract disk guid */
 	s = str;
@@ -531,6 +622,88 @@ static int do_disk_guid(struct blk_desc *dev_desc, char * const namestr)
 	return ret;
 }
 
+#ifdef CONFIG_CMD_GPT_FLIP
+static int do_flip_gpt_parts(struct blk_desc *dev_desc)
+{
+	struct list_head *pos;
+	struct disk_part *curr;
+	disk_partition_t *new_partitions = NULL;
+	char disk_guid[UUID_STR_LEN + 1];
+	char *partitions_list, *str_disk_guid;
+	u8 part_count = 0;
+	int partlistlen, ret, numparts = 0;
+
+	ret = get_disk_guid(dev_desc, disk_guid);
+	if (ret < 0)
+		return ret;
+
+	numparts = get_gpt_info(dev_desc);
+	if (numparts <  0)
+		return numparts;
+	printf("Current partition table with %d partitions is:\n", numparts);
+	print_gpt_info();
+
+	partlistlen = calc_parts_list_len(numparts);
+	partitions_list = (char *)malloc(partlistlen);
+	memset(partitions_list, '\0', partlistlen);
+
+	ret = create_gpt_partitions_list(numparts, (const char *) disk_guid,
+					 partitions_list);
+	if (ret < 0)
+		return ret;
+	debug("OLD partitions_list is %s with %u chars\n", partitions_list,
+	      (unsigned)strlen(partitions_list));
+
+	ret = set_gpt_info(dev_desc, (const char *)partitions_list, &str_disk_guid,
+			   &new_partitions, &part_count);
+	if (ret < 0)
+		return ret;
+
+	list_for_each(pos, &disk_partitions) {
+		curr = list_entry(pos, struct disk_part, list);
+		if (!strcmp((char *)curr->gpt_part_info.name, "backup_kernel"))
+			strcpy((char *)curr->gpt_part_info.name, "candidate_kernel");
+		if (!strcmp((char *)curr->gpt_part_info.name, "primary_kernel"))
+			strcpy((char *)curr->gpt_part_info.name, "backup_kernel");
+		if (!strcmp((char *)curr->gpt_part_info.name, "backup_rootfs"))
+			strcpy((char *)curr->gpt_part_info.name, "candidate_rootfs");
+		if (!strcmp((char *)curr->gpt_part_info.name, "primary_rootfs"))
+			strcpy((char *)curr->gpt_part_info.name, "backup_rootfs");
+	}
+
+	ret = create_gpt_partitions_list(numparts, (const char *) disk_guid, partitions_list);
+	if (ret < 0)
+		return ret;
+	debug("NEW partitions_list is %s with %u chars\n", partitions_list,
+	      (unsigned)strlen(partitions_list));
+
+	ret = set_gpt_info(dev_desc, (const char *)partitions_list, &str_disk_guid,
+			   &new_partitions, &part_count);
+	if (ret < 0)
+		return ret;
+
+	debug("Writing new partition table\n");
+	ret = gpt_restore(dev_desc, disk_guid, new_partitions, numparts);
+	if (ret < 0) {
+		printf("Writing new partition table failed\n");
+		return ret;
+	}
+
+	debug("Reading back new partition table\n");
+	numparts = get_gpt_info(dev_desc);
+	if (numparts <  0)
+		return numparts;
+	printf("new partition table with %d partitions is:\n", numparts);
+	print_gpt_info();
+
+	del_gpt_info();
+	free(partitions_list);
+	free(str_disk_guid);
+	free(new_partitions);
+	return ret;
+}
+#endif
+
 /**
  * do_gpt(): Perform GPT operations
  *
@@ -573,6 +746,10 @@ static int do_gpt(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 		ret = do_disk_guid(blk_dev_desc, argv[4]);
 	} else if (strcmp(argv[1], "read") == 0) {
 		ret = do_get_gpt_info(blk_dev_desc);
+#ifdef CONFIG_CMD_GPT_FLIP
+	} else if (strcmp(argv[1], "flip") == 0) {
+		ret = do_flip_gpt_parts(blk_dev_desc);
+#endif
 	} else {
 		return CMD_RET_USAGE;
 	}
@@ -604,4 +781,9 @@ U_BOOT_CMD(gpt, CONFIG_SYS_MAXARGS, 1, do_gpt,
 	" Example usage:\n"
 	" gpt guid mmc 0\n"
 	" gpt guid mmc 0 varname\n"
+#ifdef CONFIG_CMD_GPT_FLIP
+	"gpt partition-flip command\n"
+	"gpt flip <interface> <dev>\n"
+	"    - exchange device's 'primary' and 'backup' partition names\n"
+#endif
 );
diff --git a/doc/README.gpt b/doc/README.gpt
index c0779a4..e29b188 100644
--- a/doc/README.gpt
+++ b/doc/README.gpt
@@ -210,6 +210,19 @@ Following line can be used to assess if GPT verification has succeed:
 U-BOOT> gpt verify mmc 0 $partitions
 U-BOOT> if test $? = 0; then echo "GPT OK"; else echo "GPT ERR"; fi
 
+Renaming GPT partitions from U-Boot:
+====================================
+
+GPT partition names are a mechanism via which userspace and U-Boot can
+communicate about software updates and boot failure.  The 'gpt guid',
+'gpt read' and 'gpt flip' commands facilitate programmatic renaming of
+partitions from bootscripts by generating and modifying the partitions
+layout string.  The code in gpt_flip() illustrates the case of
+swapping 'primary' and 'backup' partitions via:
+
+U-BOOT> gpt flip mmc 0
+
+Choose different partition names by modifying these strings in gpt.c.
 
 Partition type GUID:
 ====================
-- 
2.1.4



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