btrfs: use raid_attr to adjust minimal stripe size in btrfs_calc_avail_data_space

Special case for DUP can be replaced by lookup to the attribute table,
where the dev_stripes is the right coefficient.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/super.c

@@ -1904,6 +1904,7 @@ static inline int btrfs_calc_avail_data_space(struct btrfs_fs_info *fs_info,
 	u64 min_stripe_size;
 	int min_stripes = 1, num_stripes = 1;
 	int i = 0, nr_devices;
+	const struct btrfs_raid_attr *rattr;
 
 	/*
 	 * We aren't under the device list lock, so this is racy-ish, but good
@@ -1927,6 +1928,8 @@ static inline int btrfs_calc_avail_data_space(struct btrfs_fs_info *fs_info,
 
 	/* calc min stripe number for data space allocation */
 	type = btrfs_data_alloc_profile(fs_info);
+	rattr = &btrfs_raid_array[btrfs_bg_flags_to_raid_index(type)];
+
 	if (type & BTRFS_BLOCK_GROUP_RAID0) {
 		min_stripes = 2;
 		num_stripes = nr_devices;
@@ -1938,10 +1941,8 @@ static inline int btrfs_calc_avail_data_space(struct btrfs_fs_info *fs_info,
 		num_stripes = 4;
 	}
 
-	if (type & BTRFS_BLOCK_GROUP_DUP)
-		min_stripe_size = 2 * BTRFS_STRIPE_LEN;
-	else
-		min_stripe_size = BTRFS_STRIPE_LEN;
+	/* Adjust for more than 1 stripe per device */
+	min_stripe_size = rattr->dev_stripes * BTRFS_STRIPE_LEN;
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(device, &fs_devices->devices, dev_list) {