btrfs: add btrfs_try_lock_ordered_range

For IOCB_NOWAIT we're going to want to use try lock on the extent lock,
and simply bail if there's an ordered extent in the range because the
only choice there is to wait for the ordered extent to complete.
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Stefan Roesch <shr@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ordered-data.c

@@ -1062,6 +1062,31 @@ void btrfs_lock_and_flush_ordered_range(struct btrfs_inode *inode, u64 start,
 	}
 }
 
+/*
+ * Lock the passed range and ensure all pending ordered extents in it are run
+ * to completion in nowait mode.
+ *
+ * Return true if btrfs_lock_ordered_range does not return any extents,
+ * otherwise false.
+ */
+bool btrfs_try_lock_ordered_range(struct btrfs_inode *inode, u64 start, u64 end)
+{
+	struct btrfs_ordered_extent *ordered;
+
+	if (!try_lock_extent(&inode->io_tree, start, end))
+		return false;
+
+	ordered = btrfs_lookup_ordered_range(inode, start, end - start + 1);
+	if (!ordered)
+		return true;
+
+	btrfs_put_ordered_extent(ordered);
+	unlock_extent(&inode->io_tree, start, end, NULL);
+
+	return false;
+}
+
+
 static int clone_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pos,
 				u64 len)
 {

fs/btrfs/ordered-data.h

@@ -206,6 +206,7 @@ void btrfs_wait_ordered_roots(struct btrfs_fs_info *fs_info, u64 nr,
 void btrfs_lock_and_flush_ordered_range(struct btrfs_inode *inode, u64 start,
 					u64 end,
 					struct extent_state **cached_state);
+bool btrfs_try_lock_ordered_range(struct btrfs_inode *inode, u64 start, u64 end);
 int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pre,
 			       u64 post);
 int __init ordered_data_init(void);