btrfs: Refactor btrfs_rmap_block to improve readability

Move variables to appropriate scope. Remove last BUG_ON in the function
and rework error handling accordingly. Make the duplicate detection code
more straightforward. Use in_range macro. And give variables more
descriptive name by explicitly distinguishing between IO stripe size
(size recorded in the chunk item) and data stripe size (the size of
an actual stripe, constituting a logical chunk/block group).

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -1582,34 +1582,43 @@ int btrfs_rmap_block(struct btrfs_fs_info *fs_info, u64 chunk_start,
 	struct map_lookup *map;
 	u64 *buf;
 	u64 bytenr;
-	u64 length;
-	u64 stripe_nr;
-	u64 rmap_len;
-	int i, j, nr = 0;
+	u64 data_stripe_length;
+	u64 io_stripe_size;
+	int i, nr = 0;
+	int ret = 0;
 
 	em = btrfs_get_chunk_map(fs_info, chunk_start, 1);
 	if (IS_ERR(em))
 		return -EIO;
 
 	map = em->map_lookup;
-	length = em->len;
-	rmap_len = map->stripe_len;
+	data_stripe_length = em->len;
+	io_stripe_size = map->stripe_len;
 
 	if (map->type & BTRFS_BLOCK_GROUP_RAID10)
-		length = div_u64(length, map->num_stripes / map->sub_stripes);
+		data_stripe_length = div_u64(data_stripe_length,
+					     map->num_stripes / map->sub_stripes);
 	else if (map->type & BTRFS_BLOCK_GROUP_RAID0)
-		length = div_u64(length, map->num_stripes);
+		data_stripe_length = div_u64(data_stripe_length, map->num_stripes);
 	else if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
-		length = div_u64(length, nr_data_stripes(map));
-		rmap_len = map->stripe_len * nr_data_stripes(map);
+		data_stripe_length = div_u64(data_stripe_length,
+					     nr_data_stripes(map));
+		io_stripe_size = map->stripe_len * nr_data_stripes(map);
 	}
 
 	buf = kcalloc(map->num_stripes, sizeof(u64), GFP_NOFS);
-	BUG_ON(!buf); /* -ENOMEM */
+	if (!buf) {
+		ret = -ENOMEM;
+		goto out;
+	}
 
 	for (i = 0; i < map->num_stripes; i++) {
-		if (map->stripes[i].physical > physical ||
-		    map->stripes[i].physical + length <= physical)
+		bool already_inserted = false;
+		u64 stripe_nr;
+		int j;
+
+		if (!in_range(physical, map->stripes[i].physical,
+			      data_stripe_length))
 			continue;
 
 		stripe_nr = physical - map->stripes[i].physical;
@@ -1627,24 +1636,26 @@ int btrfs_rmap_block(struct btrfs_fs_info *fs_info, u64 chunk_start,
 		 * instead of map->stripe_len
 		 */
 
-		bytenr = chunk_start + stripe_nr * rmap_len;
-		WARN_ON(nr >= map->num_stripes);
+		bytenr = chunk_start + stripe_nr * io_stripe_size;
+
+		/* Ensure we don't add duplicate addresses */
 		for (j = 0; j < nr; j++) {
-			if (buf[j] == bytenr)
+			if (buf[j] == bytenr) {
+				already_inserted = true;
 				break;
+			}
 		}
-		if (j == nr) {
-			WARN_ON(nr >= map->num_stripes);
+
+		if (!already_inserted)
 			buf[nr++] = bytenr;
-		}
 	}
 
 	*logical = buf;
 	*naddrs = nr;
-	*stripe_len = rmap_len;
-
+	*stripe_len = io_stripe_size;
+out:
 	free_extent_map(em);
-	return 0;
+	return ret;
 }
 
 static int exclude_super_stripes(struct btrfs_block_group *cache)