btrfs: factor out helper for counting data stripes

Factor the sequence of ifs to a helper, the 'data stripes' here means
the number of stripes without redundancy and parity.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -3474,6 +3474,18 @@ static int chunk_devid_filter(struct extent_buffer *leaf,
 	return 1;
 }
 
+static u64 calc_data_stripes(u64 type, int num_stripes)
+{
+	const int index = btrfs_bg_flags_to_raid_index(type);
+	const int ncopies = btrfs_raid_array[index].ncopies;
+	const int nparity = btrfs_raid_array[index].nparity;
+
+	if (nparity)
+		return num_stripes - nparity;
+	else
+		return num_stripes / ncopies;
+}
+
 /* [pstart, pend) */
 static int chunk_drange_filter(struct extent_buffer *leaf,
 			       struct btrfs_chunk *chunk,
@@ -3483,22 +3495,15 @@ static int chunk_drange_filter(struct extent_buffer *leaf,
 	int num_stripes = btrfs_chunk_num_stripes(leaf, chunk);
 	u64 stripe_offset;
 	u64 stripe_length;
+	u64 type;
 	int factor;
 	int i;
 
 	if (!(bargs->flags & BTRFS_BALANCE_ARGS_DEVID))
 		return 0;
 
-	if (btrfs_chunk_type(leaf, chunk) & (BTRFS_BLOCK_GROUP_DUP |
-	     BTRFS_BLOCK_GROUP_RAID1 | BTRFS_BLOCK_GROUP_RAID10)) {
-		factor = num_stripes / 2;
-	} else if (btrfs_chunk_type(leaf, chunk) & BTRFS_BLOCK_GROUP_RAID5) {
-		factor = num_stripes - 1;
-	} else if (btrfs_chunk_type(leaf, chunk) & BTRFS_BLOCK_GROUP_RAID6) {
-		factor = num_stripes - 2;
-	} else {
-		factor = num_stripes;
-	}
+	type = btrfs_chunk_type(leaf, chunk);
+	factor = calc_data_stripes(type, num_stripes);
 
 	for (i = 0; i < num_stripes; i++) {
 		stripe = btrfs_stripe_nr(chunk, i);