smb3: reenable swapfiles over SMB3 mounts

With the changes to folios/netfs it is now easier to reenable
swapfile support over SMB3 which fixes various xfstests

Reviewed-by: David Howells <[e-mail]>
Suggested-by: David Howells <[e-mail]>
Fixes: e1209d3a7a67 ("mm: introduce ->swap_rw and use it for reads from SWP_FS_OPS swap-space")
Signed-off-by: Steve French <[e-mail]>

fs/netfs/direct_write.c

···
  * Perform an unbuffered write where we may have to do an RMW operation on an
  * encrypted file.  This can also be used for direct I/O writes.
  */
-static ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,
+ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,
 						  struct netfs_group *netfs_group)
 {
 	struct netfs_io_request *wreq;
···
 	netfs_put_request(wreq, false, netfs_rreq_trace_put_return);
 	return ret;
 }
+EXPORT_SYMBOL(netfs_unbuffered_write_iter_locked);
 
 /**
  * netfs_unbuffered_write_iter - Unbuffered write to a file

fs/smb/client/file.c

···
 	/* do we need to unpin (or unlock) the file */
 }
 
+/**
+ * cifs_swap_rw - SMB3 address space operation for swap I/O
+ * @iocb: target I/O control block
+ * @iter: I/O buffer
+ *
+ * Perform IO to the swap-file.  This is much like direct IO.
+ */
+static int cifs_swap_rw(struct kiocb *iocb, struct iov_iter *iter)
+{
+	ssize_t ret;
+
+	WARN_ON_ONCE(iov_iter_count(iter) != PAGE_SIZE);
+
+	if (iov_iter_rw(iter) == READ)
+		ret = netfs_unbuffered_read_iter_locked(iocb, iter);
+	else
+		ret = netfs_unbuffered_write_iter_locked(iocb, iter, NULL);
+	if (ret < 0)
+		return ret;
+	return 0;
+}
+
 const struct address_space_operations cifs_addr_ops = {
 	.read_folio	= netfs_read_folio,
 	.readahead	= netfs_readahead,
···
 	 */
 	.swap_activate	= cifs_swap_activate,
 	.swap_deactivate = cifs_swap_deactivate,
+	.swap_rw = cifs_swap_rw,
 };
 
 /*

include/linux/netfs.h

···
 ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *from,
 					 struct netfs_group *netfs_group);
 ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from);
+ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,
+					   struct netfs_group *netfs_group);
 ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from);
 
 /* Address operations API */