Btrfs, replace: write raid56 parity into the replace target device

This function reused the code of parity scrub, and we just write
the right parity or corrected parity into the target device before
the parity scrub end.
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>

fs/btrfs/raid56.c

@@ -2318,7 +2318,9 @@ static void raid_write_parity_end_io(struct bio *bio, int err)
 static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 					 int need_check)
 {
+	struct btrfs_bio *bbio = rbio->bbio;
 	void *pointers[rbio->real_stripes];
+	DECLARE_BITMAP(pbitmap, rbio->stripe_npages);
 	int nr_data = rbio->nr_data;
 	int stripe;
 	int pagenr;
@@ -2328,6 +2330,7 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 	struct page *q_page = NULL;
 	struct bio_list bio_list;
 	struct bio *bio;
+	int is_replace = 0;
 	int ret;
 
 	bio_list_init(&bio_list);
@@ -2341,6 +2344,11 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 		BUG();
 	}
 
+	if (bbio->num_tgtdevs && bbio->tgtdev_map[rbio->scrubp]) {
+		is_replace = 1;
+		bitmap_copy(pbitmap, rbio->dbitmap, rbio->stripe_npages);
+	}
+
 	/*
 	 * Because the higher layers(scrubber) are unlikely to
 	 * use this area of the disk again soon, so don't cache
@@ -2429,6 +2437,21 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 			goto cleanup;
 	}
 
+	if (!is_replace)
+		goto submit_write;
+
+	for_each_set_bit(pagenr, pbitmap, rbio->stripe_npages) {
+		struct page *page;
+
+		page = rbio_stripe_page(rbio, rbio->scrubp, pagenr);
+		ret = rbio_add_io_page(rbio, &bio_list, page,
+				       bbio->tgtdev_map[rbio->scrubp],
+				       pagenr, rbio->stripe_len);
+		if (ret)
+			goto cleanup;
+	}
+
+submit_write:
 	nr_data = bio_list_size(&bio_list);
 	if (!nr_data) {
 		/* Every parity is right */

fs/btrfs/scrub.c

@@ -2714,7 +2714,7 @@ static void scrub_parity_check_and_repair(struct scrub_parity *sparity)
 		goto out;
 
 	length = sparity->logic_end - sparity->logic_start + 1;
-	ret = btrfs_map_sblock(sctx->dev_root->fs_info, REQ_GET_READ_MIRRORS,
+	ret = btrfs_map_sblock(sctx->dev_root->fs_info, WRITE,
 			       sparity->logic_start,
 			       &length, &bbio, 0, &raid_map);
 	if (ret || !bbio || !raid_map)