Btrfs: introduce btrfs_{start, end}_nocow_write() for each subvolume

If the snapshot creation happened after the nocow write but before the dirty
data flush, we would fail to flush the dirty data because of no space.

So we must keep track of when those nocow write operations start and when they
end, if there are nocow writers, the snapshot creators must wait. In order
to implement this function, I introduce btrfs_{start, end}_nocow_write(),
which is similar to mnt_{want,drop}_write().

These two functions are only used for nocow file write operations.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index b4d2e957b89f..374bb2f8ccd9 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1681,6 +1681,11 @@ struct btrfs_fs_info {
 	unsigned int update_uuid_tree_gen:1;
 };
 
+struct btrfs_subvolume_writers {
+	struct percpu_counter	counter;
+	wait_queue_head_t	wait;
+};
+
 /*
  * in ram representation of the tree.  extent_root is used for all allocations
  * and for the extent tree extent_root root.
@@ -1829,6 +1834,8 @@ struct btrfs_root {
 	 * manipulation with the read-only status via SUBVOL_SETFLAGS
 	 */
 	int send_in_progress;
+	struct btrfs_subvolume_writers *subv_writers;
+	atomic_t will_be_snapshoted;
 };
 
 struct btrfs_ioctl_defrag_range_args {
@@ -3353,6 +3360,9 @@ int btrfs_init_space_info(struct btrfs_fs_info *fs_info);
 int btrfs_delayed_refs_qgroup_accounting(struct btrfs_trans_handle *trans,
 					 struct btrfs_fs_info *fs_info);
 int __get_raid_index(u64 flags);
+
+int btrfs_start_nocow_write(struct btrfs_root *root);
+void btrfs_end_nocow_write(struct btrfs_root *root);
 /* ctree.c */
 int btrfs_bin_search(struct extent_buffer *eb, struct btrfs_key *key,
 		     int level, int *slot);