btrfs: sink parameter len to btrfs_split_ordered_extent

btrfs_split_ordered_extent is only ever asked to split out the beginning
of an ordered_extent (i.e. post == 0).  Change it to only take a len to
split out, and switch it to allocate the new extent for the beginning,
as that helps with callers that want to keep a pointer to the
ordered_extent that it is stealing from.
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: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -2646,17 +2646,11 @@ blk_status_t btrfs_extract_ordered_extent(struct btrfs_bio *bbio)
 		goto out;
 	}
 
-	/* The bio must be entirely covered by the ordered extent. */
-	if (WARN_ON_ONCE(len > ordered_len)) {
-		ret = -EINVAL;
-		goto out;
-	}
-
 	/* No need to split if the ordered extent covers the entire bio. */
 	if (ordered->disk_num_bytes == len)
 		goto out;
 
-	ret = btrfs_split_ordered_extent(ordered, len, 0);
+	ret = btrfs_split_ordered_extent(ordered, len);
 	if (ret)
 		goto out;
 	ret = split_zoned_em(inode, bbio->file_offset, ordered_len, len, 0);

fs/btrfs/ordered-data.c

@@ -1138,17 +1138,22 @@ static int clone_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pos,
 					ordered->compress_type);
 }
 
-int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pre,
-				u64 post)
+/* Split out a new ordered extent for this first @len bytes of @ordered. */
+int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 len)
 {
 	struct inode *inode = ordered->inode;
 	struct btrfs_ordered_inode_tree *tree = &BTRFS_I(inode)->ordered_tree;
-	struct rb_node *node;
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
-	int ret = 0;
+	struct rb_node *node;
 
 	trace_btrfs_ordered_extent_split(BTRFS_I(inode), ordered);
 
+	/*
+	 * The entire bio must be covered by the ordered extent, but we can't
+	 * reduce the original extent to a zero length either.
+	 */
+	if (WARN_ON_ONCE(len >= ordered->num_bytes))
+		return -EINVAL;
 	/* We cannot split once ordered extent is past end_bio. */
 	if (WARN_ON_ONCE(ordered->bytes_left != ordered->disk_num_bytes))
 		return -EINVAL;
@@ -1167,11 +1172,11 @@ int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pre,
 	if (tree->last == node)
 		tree->last = NULL;
 
-	ordered->file_offset += pre;
-	ordered->disk_bytenr += pre;
-	ordered->num_bytes -= (pre + post);
-	ordered->disk_num_bytes -= (pre + post);
-	ordered->bytes_left -= (pre + post);
+	ordered->file_offset += len;
+	ordered->disk_bytenr += len;
+	ordered->num_bytes -= len;
+	ordered->disk_num_bytes -= len;
+	ordered->bytes_left -= len;
 
 	/* Re-insert the node */
 	node = tree_insert(&tree->tree, ordered->file_offset, &ordered->rb_node);
@@ -1182,13 +1187,7 @@ int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pre,
 
 	spin_unlock_irq(&tree->lock);
 
-	if (pre)
-		ret = clone_ordered_extent(ordered, 0, pre);
-	if (ret == 0 && post)
-		ret = clone_ordered_extent(ordered, pre + ordered->disk_num_bytes,
-					   post);
-
-	return ret;
+	return clone_ordered_extent(ordered, 0, len);
 }
 
 int __init ordered_data_init(void)

fs/btrfs/ordered-data.h

@@ -212,8 +212,7 @@ void btrfs_lock_and_flush_ordered_range(struct btrfs_inode *inode, u64 start,
 					struct extent_state **cached_state);
 bool btrfs_try_lock_ordered_range(struct btrfs_inode *inode, u64 start, u64 end,
 				  struct extent_state **cached_state);
-int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pre,
-			       u64 post);
+int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 len);
 int __init ordered_data_init(void);
 void __cold ordered_data_exit(void);