[U-Boot] [PATCH v3 4/5] rename GPT partitions to detect boot failure

alison at peloton-tech.com
2017-06-03T02:22:33Z

From: Alison Chaiken <alison@peloton-tech.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.

Signed-off-by: Alison Chaiken <alison@peloton-tech.com>
---
cmd/Kconfig | 7 ++
cmd/gpt.c | 199 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--
doc/README.gpt | 13 ++++
3 files changed, 215 insertions(+), 4 deletions(-)

diff --git a/cmd/Kconfig b/cmd/Kconfig
index 6f75b86..8b925e5 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 5c2651f..f6968de 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);

@@ -190,16 +191,33 @@ 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,
@@ -211,6 +229,85 @@ static void print_gpt_info(void)
}
}

+#ifdef CONFIG_CMD_GPT_FLIP
+static int calc_parts_list_len(int numparts)
+{
+ /*
+ * prefatory string:
+ * doc/README.GPT, suggests that
+ * int partlistlen = UUID_STR_LEN + 1 + strlen("partitions=uuid_disk=");
+ * is correct, but extract_val() expects "uuid_disk" first.
+ */
+ 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);
+ /* 17 because partstr in create_gpt_partitions_list() is 16 chars */
+ partlistlen += numparts * (strlen("start=MiB,") + 17);
+ partlistlen += numparts * (strlen("size=MiB,") + 17);
+ 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:
+ * "partitions=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;
+
+ /*
+ * README.gpt specifies starting with "partitions=" like so:
+ * strcpy(partitions_list, "partitions=uuid_disk=");
+ * but that breaks extract_val, which doesn't skip over 'partitions='.
+ */
+ 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
@@ -222,8 +319,11 @@ 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);
@@ -294,6 +394,8 @@ 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;
@@ -523,6 +625,86 @@ 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 %d chars\n", partitions_list, 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 %d chars\n", partitions_list, 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
*
@@ -565,6 +747,10 @@ static int do_gpt(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
return do_disk_guid(blk_dev_desc, argv[4]);
} else if (strcmp(argv[1], "read") == 0) {
return do_get_gpt_info(blk_dev_desc);
+#ifdef CONFIG_CMD_GPT_FLIP
+ } else if (strcmp(argv[1], "flip") == 0) {
+ return do_flip_gpt_parts(blk_dev_desc);
+#endif
} else {
return CMD_RET_USAGE;
}
@@ -596,4 +782,9 @@ 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