+ if (dev_replace_is_ongoing && (rw & (REQ_WRITE | REQ_DISCARD)) &&
+ dev_replace->tgtdev != NULL) {
+ int index_where_to_add;
+ u64 srcdev_devid = dev_replace->srcdev->devid;
+
+ /*
+ * duplicate the write operations while the dev replace
+ * procedure is running. Since the copying of the old disk
+ * to the new disk takes place at run time while the
+ * filesystem is mounted writable, the regular write
+ * operations to the old disk have to be duplicated to go
+ * to the new disk as well.
+ * Note that device->missing is handled by the caller, and
+ * that the write to the old disk is already set up in the
+ * stripes array.
+ */
+ index_where_to_add = num_stripes;
+ for (i = 0; i < num_stripes; i++) {
+ if (bbio->stripes[i].dev->devid == srcdev_devid) {
+ /* write to new disk, too */
+ struct btrfs_bio_stripe *new =
+ bbio->stripes + index_where_to_add;
+ struct btrfs_bio_stripe *old =
+ bbio->stripes + i;
+
+ new->physical = old->physical;
+ new->length = old->length;
+ new->dev = dev_replace->tgtdev;
+ index_where_to_add++;
+ max_errors++;
+ }
+ }
+ num_stripes = index_where_to_add;
+ }
+