UBI: add ubi_leb_map interface

The idea of this interface belongs to Adrian Hunter. The
interface is extremely useful when one has to have a guarantee
that an LEB will contain all 0xFFs even in case of an unclean
reboot. UBI does have an 'ubi_leb_erase()' call which may do
this, but it is stupid and ineffecient, because it flushes whole
queue. I should be re-worked to just be a pair of unmap,
map calls.

The user of the interfaci is UBIFS at the moment.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

drivers/mtd/ubi/eba.c

@@ -656,11 +656,14 @@ retry:
 		goto write_error;
 	}
 
-	err = ubi_io_write_data(ubi, buf, pnum, offset, len);
-	if (err) {
-		ubi_warn("failed to write %d bytes at offset %d of LEB %d:%d, "
-			 "PEB %d", len, offset, vol_id, lnum, pnum);
-		goto write_error;
+	if (len) {
+		err = ubi_io_write_data(ubi, buf, pnum, offset, len);
+		if (err) {
+			ubi_warn("failed to write %d bytes at offset %d of "
+				 "LEB %d:%d, PEB %d", len, offset, vol_id,
+				 lnum, pnum);
+			goto write_error;
+		}
 	}
 
 	vol->eba_tbl[lnum] = pnum;

drivers/mtd/ubi/kapi.c

@@ -546,6 +546,51 @@ int ubi_leb_unmap(struct ubi_volume_desc *desc, int lnum)
 }
 EXPORT_SYMBOL_GPL(ubi_leb_unmap);
 
+/**
+ * ubi_leb_map - map logical erasblock to a physical eraseblock.
+ * @desc: volume descriptor
+ * @lnum: logical eraseblock number
+ * @dtype: expected data type
+ *
+ * This function maps an un-mapped logical eraseblock @lnum to a physical
+ * eraseblock. This means, that after a successfull invocation of this
+ * function the logical eraseblock @lnum will be empty (contain only %0xFF
+ * bytes) and be mapped to a physical eraseblock, even if an unclean reboot
+ * happens.
+ *
+ * This function returns zero in case of success, %-EBADF if the volume is
+ * damaged because of an interrupted update, %-EBADMSG if the logical
+ * eraseblock is already mapped, and other negative error codes in case of
+ * other failures.
+ */
+int ubi_leb_map(struct ubi_volume_desc *desc, int lnum, int dtype)
+{
+	struct ubi_volume *vol = desc->vol;
+	struct ubi_device *ubi = vol->ubi;
+	int vol_id = vol->vol_id;
+
+	dbg_msg("unmap LEB %d:%d", vol_id, lnum);
+
+	if (desc->mode == UBI_READONLY || vol->vol_type == UBI_STATIC_VOLUME)
+		return -EROFS;
+
+	if (lnum < 0 || lnum >= vol->reserved_pebs)
+		return -EINVAL;
+
+	if (dtype != UBI_LONGTERM && dtype != UBI_SHORTTERM &&
+	    dtype != UBI_UNKNOWN)
+		return -EINVAL;
+
+	if (vol->upd_marker)
+		return -EBADF;
+
+	if (vol->eba_tbl[lnum] >= 0)
+		return -EBADMSG;
+
+	return ubi_eba_write_leb(ubi, vol_id, lnum, NULL, 0, 0, dtype);
+}
+EXPORT_SYMBOL_GPL(ubi_leb_map);
+
 /**
  * ubi_is_mapped - check if logical eraseblock is mapped.
  * @desc: volume descriptor

include/linux/mtd/ubi.h

@@ -167,6 +167,7 @@ int ubi_leb_change(struct ubi_volume_desc *desc, int lnum, const void *buf,
 		   int len, int dtype);
 int ubi_leb_erase(struct ubi_volume_desc *desc, int lnum);
 int ubi_leb_unmap(struct ubi_volume_desc *desc, int lnum);
+int ubi_leb_map(struct ubi_volume_desc *desc, int lnum, int dtype);
 int ubi_is_mapped(struct ubi_volume_desc *desc, int lnum);
 
 /*