util-net: Add declaration of scm_fdset structure

This structure will serve for multiple fds transmission/receive.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/util-net.h

 #ifndef UTIL_NET_H_
 #define UTIL_NET_H_
 
+#include <sys/socket.h>
+#include <sys/un.h>
+
 #define UNIX_PATH_MAX (sizeof(struct sockaddr_un) - \
 			(size_t)((struct sockaddr_un *) 0)->sun_path)
 
@@ -8,6 +11,23 @@
 #define SO_PEEK_OFF            42
 #endif
 
+/*
+ * Because of kernel doing kmalloc for user data passed
+ * in SCM messages, and there is SCM_MAX_FD as a limit
+ * for descriptors passed at once we're trying to reduce
+ * the pressue on kernel memory manager and use predefined
+ * known to work well size of the message buffer.
+ */
+#define CR_SCM_MSG_SIZE		(1024)
+#define CR_SCM_MAX_FD		(252)
+
+struct scm_fdset {
+	struct msghdr	hdr;
+	struct iovec	iov;
+	char		msg_buf[CR_SCM_MSG_SIZE];
+	int		msg;	/* We are to send at least one byte */
+};
+
 extern int send_fd(int sock, struct sockaddr_un *saddr, int len, int fd);
 extern int recv_fd(int sock);
 #endif