btrfs: zoned: implement active zone tracking

Add zone_is_active flag to btrfs_block_group. This flag indicates the
underlying zones are all active. Such zone active block groups are tracked
by fs_info->active_bg_list.

btrfs_dev_{set,clear}_active_zone() take responsibility for the underlying
device part. They set/clear the bitmap to indicate zone activeness and
count the number of zones we can activate left.

btrfs_zone_{activate,finish}() take responsibility for the logical part and
the list management. In addition, btrfs_zone_finish() wait for any writes
on it and send REQ_OP_ZONE_FINISH to the zone.

Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/block-group.h b/fs/btrfs/block-group.h
index 265db2c..f751b80 100644
--- a/fs/btrfs/block-group.h
+++ b/fs/btrfs/block-group.h
@@ -98,6 +98,7 @@ struct btrfs_block_group {
 	unsigned int to_copy:1;
 	unsigned int relocating_repair:1;
 	unsigned int chunk_item_inserted:1;
+	unsigned int zone_is_active:1;
 
 	int disk_cache_state;
 
@@ -205,6 +206,7 @@ struct btrfs_block_group {
 	u64 zone_capacity;
 	u64 meta_write_pointer;
 	struct map_lookup *physical_map;
+	struct list_head active_bg_list;
 };
 
 static inline u64 btrfs_block_group_end(struct btrfs_block_group *block_group)