UBI: add image sequence number to EC header

An image sequence number is added to the UBI erase-counter header
to be able determine if the root file system contains a mixture
of old and new images (because the flashing failed to complete).

A change to nolo is also needed for this to take effect.

Signed-off-by: Adrian Hunter <[e-mail]>
Signed-off-by: Artem Bityutskiy <[e-mail]>

drivers/mtd/ubi/build.c

···
 	ubi_msg("number of PEBs reserved for bad PEB handling: %d",
 		ubi->beb_rsvd_pebs);
 	ubi_msg("max/mean erase counter: %d/%d", ubi->max_ec, ubi->mean_ec);
+	ubi_msg("image sequence number: %d", ubi->image_seq);
 
 	/*
 	 * The below lock makes sure we do not race with 'ubi_thread()' which

drivers/mtd/ubi/debug.c

···
 	       be32_to_cpu(ec_hdr->vid_hdr_offset));
 	printk(KERN_DEBUG "\tdata_offset    %d\n",
 	       be32_to_cpu(ec_hdr->data_offset));
+	printk(KERN_DEBUG "\timage_seq      %d\n",
+	       be32_to_cpu(ec_hdr->image_seq));
 	printk(KERN_DEBUG "\thdr_crc        %#08x\n",
 	       be32_to_cpu(ec_hdr->hdr_crc));
 	printk(KERN_DEBUG "erase counter header hexdump:\n");

drivers/mtd/ubi/io.c

···
  * This function returns zero if the erase counter header is OK, and %1 if
  * not.
  */
-static int validate_ec_hdr(const struct ubi_device *ubi,
+static int validate_ec_hdr(struct ubi_device *ubi,
 			   const struct ubi_ec_hdr *ec_hdr)
 {
 	long long ec;
-	int vid_hdr_offset, leb_start;
+	int vid_hdr_offset, leb_start, image_seq;
 
 	ec = be64_to_cpu(ec_hdr->ec);
 	vid_hdr_offset = be32_to_cpu(ec_hdr->vid_hdr_offset);
 	leb_start = be32_to_cpu(ec_hdr->data_offset);
+	image_seq = be32_to_cpu(ec_hdr->image_seq);
 
 	if (ec_hdr->version != UBI_VERSION) {
 		ubi_err("node with incompatible UBI version found: "
···
 
 	if (ec < 0 || ec > UBI_MAX_ERASECOUNTER) {
 		ubi_err("bad erase counter %lld", ec);
+		goto bad;
+	}
+
+	if (!ubi->image_seq_set) {
+		ubi->image_seq = image_seq;
+		ubi->image_seq_set = 1;
+	} else if (ubi->image_seq != image_seq) {
+		ubi_err("bad image sequence number %d, expected %d",
+			image_seq, ubi->image_seq);
 		goto bad;
 	}
 
···
 	ec_hdr->version = UBI_VERSION;
 	ec_hdr->vid_hdr_offset = cpu_to_be32(ubi->vid_hdr_offset);
 	ec_hdr->data_offset = cpu_to_be32(ubi->leb_start);
+	ec_hdr->image_seq = cpu_to_be32(ubi->image_seq);
 	crc = crc32(UBI_CRC32_INIT, ec_hdr, UBI_EC_HDR_SIZE_CRC);
 	ec_hdr->hdr_crc = cpu_to_be32(crc);
 

drivers/mtd/ubi/scan.c

···
 	if (si->is_empty)
 		ubi_msg("empty MTD device detected");
 
+	ubi->image_seq_set = 1;
+
 	/*
 	 * In case of unknown erase counter we use the mean erase counter
 	 * value.

drivers/mtd/ubi/ubi-media.h

···
  * @ec: the erase counter
  * @vid_hdr_offset: where the VID header starts
  * @data_offset: where the user data start
+ * @image_seq: image sequence number
  * @padding2: reserved for future, zeroes
  * @hdr_crc: erase counter header CRC checksum
  *
···
  * volume identifier header and user data, relative to the beginning of the
  * physical eraseblock. These values have to be the same for all physical
  * eraseblocks.
+ *
+ * The @image_seq field is used to validate a UBI image that has been prepared
+ * for a UBI device. The @image_seq value can be any value, but it must be the
+ * same on all eraseblocks. UBI will ensure that all new erase counter headers
+ * also contain this value, and will check the value when scanning at start-up.
+ * One way to make use of @image_seq is to increase its value by one every time
+ * an image is flashed over an existing image, then, if the flashing does not
+ * complete, UBI will detect the error when scanning.
  */
 struct ubi_ec_hdr {
 	__be32  magic;
···
 	__be64  ec; /* Warning: the current limit is 31-bit anyway! */
 	__be32  vid_hdr_offset;
 	__be32  data_offset;
-	__u8    padding2[36];
+	__be32  image_seq;
+	__u8    padding2[32];
 	__be32  hdr_crc;
 } __attribute__ ((packed));
 

drivers/mtd/ubi/ubi.h

···
  *                @vol->readers, @vol->writers, @vol->exclusive,
  *                @vol->ref_count, @vol->mapping and @vol->eba_tbl.
  * @ref_count: count of references on the UBI device
+ * @image_seq: image sequence number recorded on EC headers
+ * @image_seq_set: indicates @image_seq is known
  *
  * @rsvd_pebs: count of reserved physical eraseblocks
  * @avail_pebs: count of available physical eraseblocks
···
 	struct ubi_volume *volumes[UBI_MAX_VOLUMES+UBI_INT_VOL_COUNT];
 	spinlock_t volumes_lock;
 	int ref_count;
+	int image_seq;
+	int image_seq_set;
 
 	int rsvd_pebs;
 	int avail_pebs;