btrfs: add function to create and return an ordered extent

Currently, btrfs_add_ordered_extent allocates a new ordered extent, adds
it to the rb_tree, but doesn't return a referenced pointer to the
caller. There are cases where it is useful for the creator of a new
ordered_extent to hang on to such a pointer, so add a new function
btrfs_alloc_ordered_extent which is the same as
btrfs_add_ordered_extent, except it takes an additional reference count
and returns a pointer to the ordered_extent. Implement
btrfs_add_ordered_extent as btrfs_alloc_ordered_extent followed by
dropping the new reference and handling the IS_ERR case.

The type of flags in btrfs_alloc_ordered_extent and
btrfs_add_ordered_extent is changed from unsigned int to unsigned long
so it's unified with the other ordered extent functions.
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Tested-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ordered-data.c

@@ -160,14 +160,16 @@ static inline struct rb_node *tree_search(struct btrfs_ordered_inode_tree *tree,
  * @compress_type:   Compression algorithm used for data.
  *
  * Most of these parameters correspond to &struct btrfs_file_extent_item. The
- * tree is given a single reference on the ordered extent that was inserted.
+ * tree is given a single reference on the ordered extent that was inserted, and
+ * the returned pointer is given a second reference.
  *
- * Return: 0 or -ENOMEM.
+ * Return: the new ordered extent or error pointer.
  */
-int btrfs_add_ordered_extent(struct btrfs_inode *inode, u64 file_offset,
-			     u64 num_bytes, u64 ram_bytes, u64 disk_bytenr,
-			     u64 disk_num_bytes, u64 offset, unsigned flags,
-			     int compress_type)
+struct btrfs_ordered_extent *btrfs_alloc_ordered_extent(
+			struct btrfs_inode *inode, u64 file_offset,
+			u64 num_bytes, u64 ram_bytes, u64 disk_bytenr,
+			u64 disk_num_bytes, u64 offset, unsigned long flags,
+			int compress_type)
 {
 	struct btrfs_root *root = inode->root;
 	struct btrfs_fs_info *fs_info = root->fs_info;
@@ -181,7 +183,7 @@ int btrfs_add_ordered_extent(struct btrfs_inode *inode, u64 file_offset,
 		/* For nocow write, we can release the qgroup rsv right now */
 		ret = btrfs_qgroup_free_data(inode, NULL, file_offset, num_bytes);
 		if (ret < 0)
-			return ret;
+			return ERR_PTR(ret);
 		ret = 0;
 	} else {
 		/*
@@ -190,11 +192,11 @@ int btrfs_add_ordered_extent(struct btrfs_inode *inode, u64 file_offset,
 		 */
 		ret = btrfs_qgroup_release_data(inode, file_offset, num_bytes);
 		if (ret < 0)
-			return ret;
+			return ERR_PTR(ret);
 	}
 	entry = kmem_cache_zalloc(btrfs_ordered_extent_cache, GFP_NOFS);
 	if (!entry)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	entry->file_offset = file_offset;
 	entry->num_bytes = num_bytes;
@@ -256,6 +258,32 @@ int btrfs_add_ordered_extent(struct btrfs_inode *inode, u64 file_offset,
 	btrfs_mod_outstanding_extents(inode, 1);
 	spin_unlock(&inode->lock);
 
+	/* One ref for the returned entry to match semantics of lookup. */
+	refcount_inc(&entry->refs);
+
+	return entry;
+}
+
+/*
+ * Add a new btrfs_ordered_extent for the range, but drop the reference instead
+ * of returning it to the caller.
+ */
+int btrfs_add_ordered_extent(struct btrfs_inode *inode, u64 file_offset,
+			     u64 num_bytes, u64 ram_bytes, u64 disk_bytenr,
+			     u64 disk_num_bytes, u64 offset, unsigned flags,
+			     int compress_type)
+{
+	struct btrfs_ordered_extent *ordered;
+
+	ordered = btrfs_alloc_ordered_extent(inode, file_offset, num_bytes,
+					     ram_bytes, disk_bytenr,
+					     disk_num_bytes, offset, flags,
+					     compress_type);
+
+	if (IS_ERR(ordered))
+		return PTR_ERR(ordered);
+	btrfs_put_ordered_extent(ordered);
+
 	return 0;
 }
 

fs/btrfs/ordered-data.h

@@ -178,6 +178,11 @@ void btrfs_mark_ordered_io_finished(struct btrfs_inode *inode,
 bool btrfs_dec_test_ordered_pending(struct btrfs_inode *inode,
 				    struct btrfs_ordered_extent **cached,
 				    u64 file_offset, u64 io_size);
+struct btrfs_ordered_extent *btrfs_alloc_ordered_extent(
+			struct btrfs_inode *inode, u64 file_offset,
+			u64 num_bytes, u64 ram_bytes, u64 disk_bytenr,
+			u64 disk_num_bytes, u64 offset, unsigned long flags,
+			int compress_type);
 int btrfs_add_ordered_extent(struct btrfs_inode *inode, u64 file_offset,
 			     u64 num_bytes, u64 ram_bytes, u64 disk_bytenr,
 			     u64 disk_num_bytes, u64 offset, unsigned flags,