Add implementations of sendmmsg(3) and recvmmsg(3) functions which

wraps sendmsg(2) and recvmsg(2) into batch send and receive operation.
The goal of this implementation is only to provide API compatibility
with Linux.

The cancellation behaviour of the functions is not quite right, but
due to relative rare use of cancellation it is considered acceptable
comparing with the complexity of the correct implementation.  If
functions are reimplemented as syscalls, the fix would come almost
trivial.  The direct use of the syscall trampolines instead of libc
wrappers for sendmsg(2) and recvmsg(2) is to avoid data loss on
cancellation.

Submitted by:	Boris Astardzhiev <boris.astardzhiev@gmail.com>
Discussed with:	jilles (cancellation behaviour)
MFC after:	1 month

1 files changed, 64 insertions, 0 deletions

diff --git a/lib/libc/gen/sendmmsg.c b/lib/libc/gen/sendmmsg.c
new file mode 100644
index 000000000000..7b3e8f357613
--- /dev/null
+++ b/lib/libc/gen/sendmmsg.c
@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2016 Boris Astardzhiev, Smartcom-Bulgaria AD
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice(s), this list of conditions and the following disclaimer as
+ *    the first lines of this file unmodified other than the possible
+ *    addition of one or more copyright notices.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice(s), this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+ * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+ * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+ * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include "libc_private.h"
+
+ssize_t
+sendmmsg(int s, struct mmsghdr *__restrict msgvec, size_t vlen, int flags)
+{
+	size_t i, sent;
+	ssize_t ret;
+
+	sent = 0;
+	for (i = 0; i < vlen; i++, sent++) {
+		ret = __sys_sendmsg(s, &msgvec[i].msg_hdr, flags);
+		if (ret == -1) {
+			if (sent != 0) {
+				/*
+				 * We have sent messages. Let caller
+				 * know about the data sent, socket
+				 * error is returned on next
+				 * invocation.
+				 */
+				return (sent);
+			}
+			return (ret);
+		}
+
+		/* Save sent bytes. */
+		msgvec[i].msg_len = ret;
+	}
+
+	return (sent);
+}