UBI: add truly corrupted PEBs to corrupted list

Start using the 'corr' list and add there PEBs which look truly corrupted,
which means they have corrupted VID header and the data which follows the
corrupted header does not contain all 0xFF bytes.

At the moment, this does not change UBI functionality much because these
PEBs will be erase when scanning finishes. But the plan is to teach UBI
preserving them.

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

drivers/mtd/ubi/scan.c

···
  * @ec: erase counter of the physical eraseblock
  *
  * This function adds corrupted physical eraseblock @pnum to the 'corr' list.
- * Returns zero in case of success and a negative error code in case of
- * failure.
+ * The corruption was presumably not caused by a power cut. Returns zero in
+ * case of success and a negative error code in case of failure.
  */
 static int add_corrupted(struct ubi_scan_info *si, int pnum, int ec)
 {
···
 }
 
 /**
+ * check_data_ff - make sure PEB contains only 0xFF data.
+ * @ubi: UBI device description object
+ * @vid_hrd: the (corrupted) VID header of this PEB
+ * @pnum: the physical eraseblock number to check
+ *
+ * This is a helper function which is used to distinguish between VID header
+ * corruptions caused by power cuts and other reasons. If the PEB contains only
+ * 0xFF bytes at the data area, the VID header is most probably corrupted
+ * because of a power cut (%0 is returned in this case). Otherwise, it was
+ * corrupted for some other reasons (%1 is returned in this case). A negative
+ * error code is returned if a read error occurred.
+ *
+ * If the corruption reason was a power cut, UBI can safely erase this PEB.
+ * Otherwise, it should preserve it to avoid possibly destroying important
+ * information.
+ */
+static int check_data_ff(struct ubi_device *ubi, struct ubi_vid_hdr *vid_hdr,
+			 int pnum)
+{
+	int err;
+
+	mutex_lock(&ubi->buf_mutex);
+	memset(ubi->peb_buf1, 0x00, ubi->leb_size);
+
+	err = ubi_io_read(ubi, ubi->peb_buf1, pnum, ubi->leb_start,
+			  ubi->leb_size);
+	if (err && err != UBI_IO_BITFLIPS && err != -EBADMSG)
+		return err;
+
+	if (ubi_check_pattern(ubi->peb_buf1, 0xFF, ubi->leb_size)) {
+		mutex_unlock(&ubi->buf_mutex);
+		return 0;
+	}
+
+	ubi_err("PEB %d contains corrupted VID header, and the data does not "
+		"contain all 0xFF, this may be a non-UBI PEB or a severe VID "
+		"header corruption which requires manual inspection", pnum);
+	ubi_dbg_dump_vid_hdr(vid_hdr);
+	dbg_msg("hexdump of PEB %d offset %d, length %d",
+		pnum, ubi->leb_start, ubi->leb_size);
+	ubi_dbg_print_hex_dump(KERN_DEBUG, "", DUMP_PREFIX_OFFSET, 32, 1,
+			       ubi->peb_buf1, ubi->leb_size, 1);
+	mutex_unlock(&ubi->buf_mutex);
+	return -EINVAL;
+}
+
+/**
  * process_eb - read, check UBI headers, and add them to scanning information.
  * @ubi: UBI device description object
  * @si: scanning information
···
 			 */
 			si->maybe_bad_peb_count += 1;
 	case UBI_IO_BAD_HDR:
+		if (ec_err)
+			/*
+			 * Both headers are corrupted. There is a possibility
+			 * that this a valid UBI PEB which has corresponding
+			 * LEB, but the headers are corrupted. However, it is
+			 * impossible to distinguish it from a PEB which just
+			 * contains garbage because a power cut during erase
+			 * operation. So we just schedule this PEB for erasure.
+			 */
+			err = 0;
+		else
+			/*
+			 * The EC was OK, but the VID header is corrupted. We
+			 * have to check what is in the data area.
+			 */
+			err = check_data_ff(ubi, vidh, pnum);
+		if (!err)
+			/* This corruption is caused by a power cut */
+			err = add_to_list(si, pnum, ec, 1, &si->erase);
+		else
+			/* This is an unexpected corruption */
+			err = add_corrupted(si, pnum, ec);
+		if (err)
+			return err;
+		goto adjust_mean_ec;
 	case UBI_IO_FF_BITFLIPS:
 		err = add_to_list(si, pnum, ec, 1, &si->erase);
 		if (err)