--- a/src/os/unix/ngx_os.h
+++ b/src/os/unix/ngx_os.h
@@ -29,6 +29,7 @@ typedef struct {
     ngx_recv_pt        udp_recv;
     ngx_send_pt        send;
     ngx_send_pt        udp_send;
+    ngx_send_chain_pt  udp_send_chain;
     ngx_send_chain_pt  send_chain;
     ngx_uint_t         flags;
 } ngx_os_io_t;
@@ -49,6 +50,8 @@ ssize_t ngx_unix_send(ngx_connection_t *
 ngx_chain_t *ngx_writev_chain(ngx_connection_t *c, ngx_chain_t *in,
     off_t limit);
 ssize_t ngx_udp_unix_send(ngx_connection_t *c, u_char *buf, size_t size);
+ngx_chain_t *ngx_udp_unix_sendmsg_chain(ngx_connection_t *c, ngx_chain_t *in,
+    off_t limit);
 
 
 #if (IOV_MAX > 64)