btrfs: stash ordered extent in dio_data during iomap dio

While it is not feasible for an ordered extent to survive across the
calls btrfs_direct_write makes into __iomap_dio_rw, it is still helpful
to stash it on the dio_data in between creating it in iomap_begin and
finishing it in either end_io or iomap_end.

The specific use I have in mind is that we can check if a particular bio
is partial in submit_io without unconditionally looking up the ordered
extent. This is a preparatory patch for a later patch which does just
that.
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>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -79,6 +79,7 @@ struct btrfs_iget_args {
 struct btrfs_dio_data {
 	ssize_t submitted;
 	struct extent_changeset *data_reserved;
+	struct btrfs_ordered_extent *ordered;
 	bool data_space_reserved;
 	bool nocow_done;
 };
@@ -6965,6 +6966,7 @@ struct extent_map *btrfs_get_extent(struct btrfs_inode *inode,
 }
 
 static struct extent_map *btrfs_create_dio_extent(struct btrfs_inode *inode,
+						  struct btrfs_dio_data *dio_data,
 						  const u64 start,
 						  const u64 len,
 						  const u64 orig_start,
@@ -6975,7 +6977,7 @@ static struct extent_map *btrfs_create_dio_extent(struct btrfs_inode *inode,
 						  const int type)
 {
 	struct extent_map *em = NULL;
-	int ret;
+	struct btrfs_ordered_extent *ordered;
 
 	if (type != BTRFS_ORDERED_NOCOW) {
 		em = create_io_em(inode, start, len, orig_start, block_start,
@@ -6985,18 +6987,21 @@ static struct extent_map *btrfs_create_dio_extent(struct btrfs_inode *inode,
 		if (IS_ERR(em))
 			goto out;
 	}
-	ret = btrfs_add_ordered_extent(inode, start, len, len, block_start,
-				       block_len, 0,
+	ordered = btrfs_alloc_ordered_extent(inode, start, len, len,
+					     block_start, block_len, 0,
 					     (1 << type) |
 					     (1 << BTRFS_ORDERED_DIRECT),
 					     BTRFS_COMPRESS_NONE);
-	if (ret) {
+	if (IS_ERR(ordered)) {
 		if (em) {
 			free_extent_map(em);
 			btrfs_drop_extent_map_range(inode, start,
 						    start + len - 1, false);
 		}
-		em = ERR_PTR(ret);
+		em = ERR_CAST(ordered);
+	} else {
+		ASSERT(!dio_data->ordered);
+		dio_data->ordered = ordered;
 	}
  out:
 
@@ -7004,6 +7009,7 @@ static struct extent_map *btrfs_create_dio_extent(struct btrfs_inode *inode,
 }
 
 static struct extent_map *btrfs_new_extent_direct(struct btrfs_inode *inode,
+						  struct btrfs_dio_data *dio_data,
 						  u64 start, u64 len)
 {
 	struct btrfs_root *root = inode->root;
@@ -7019,7 +7025,7 @@ static struct extent_map *btrfs_new_extent_direct(struct btrfs_inode *inode,
 	if (ret)
 		return ERR_PTR(ret);
 
-	em = btrfs_create_dio_extent(inode, start, ins.offset, start,
+	em = btrfs_create_dio_extent(inode, dio_data, start, ins.offset, start,
 				     ins.objectid, ins.offset, ins.offset,
 				     ins.offset, BTRFS_ORDERED_REGULAR);
 	btrfs_dec_block_group_reservations(fs_info, ins.objectid);
@@ -7364,7 +7370,7 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map,
 		}
 		space_reserved = true;
 
-		em2 = btrfs_create_dio_extent(BTRFS_I(inode), start, len,
+		em2 = btrfs_create_dio_extent(BTRFS_I(inode), dio_data, start, len,
 					      orig_start, block_start,
 					      len, orig_block_len,
 					      ram_bytes, type);
@@ -7406,7 +7412,7 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map,
 			goto out;
 		space_reserved = true;
 
-		em = btrfs_new_extent_direct(BTRFS_I(inode), start, len);
+		em = btrfs_new_extent_direct(BTRFS_I(inode), dio_data, start, len);
 		if (IS_ERR(em)) {
 			ret = PTR_ERR(em);
 			goto out;
@@ -7712,6 +7718,10 @@ static int btrfs_dio_iomap_end(struct inode *inode, loff_t pos, loff_t length,
 				      pos + length - 1, NULL);
 		ret = -ENOTBLK;
 	}
+	if (write) {
+		btrfs_put_ordered_extent(dio_data->ordered);
+		dio_data->ordered = NULL;
+	}
 
 	if (write)
 		extent_changeset_free(dio_data->data_reserved);
@@ -7773,7 +7783,7 @@ static const struct iomap_dio_ops btrfs_dio_ops = {
 
 ssize_t btrfs_dio_read(struct kiocb *iocb, struct iov_iter *iter, size_t done_before)
 {
-	struct btrfs_dio_data data;
+	struct btrfs_dio_data data = { 0 };
 
 	return iomap_dio_rw(iocb, iter, &btrfs_dio_iomap_ops, &btrfs_dio_ops,
 			    IOMAP_DIO_PARTIAL, &data, done_before);
@@ -7782,7 +7792,7 @@ ssize_t btrfs_dio_read(struct kiocb *iocb, struct iov_iter *iter, size_t done_be
 struct iomap_dio *btrfs_dio_write(struct kiocb *iocb, struct iov_iter *iter,
 				  size_t done_before)
 {
-	struct btrfs_dio_data data;
+	struct btrfs_dio_data data = { 0 };
 
 	return __iomap_dio_rw(iocb, iter, &btrfs_dio_iomap_ops, &btrfs_dio_ops,
 			    IOMAP_DIO_PARTIAL, &data, done_before);