From 4abab5ad6c8465a7528ccdd5f49367da05f78bbd Mon Sep 17 00:00:00 2001
From: Vladimir Azarov <avm@intermediate-node.net>
Date: Tue, 1 Oct 2024 15:47:05 +0200
Subject: Initial version

---
 src/network/sendmmsg.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 src/network/sendmmsg.c

(limited to 'src/network/sendmmsg.c')

diff --git a/src/network/sendmmsg.c b/src/network/sendmmsg.c
new file mode 100644
index 0000000..eeae1d0
--- /dev/null
+++ b/src/network/sendmmsg.c
@@ -0,0 +1,30 @@
+#define _GNU_SOURCE
+#include <sys/socket.h>
+#include <limits.h>
+#include <errno.h>
+#include "syscall.h"
+
+int sendmmsg(int fd, struct mmsghdr *msgvec, unsigned int vlen, unsigned int flags)
+{
+#if LONG_MAX > INT_MAX
+	/* Can't use the syscall directly because the kernel has the wrong
+	 * idea for the types of msg_iovlen, msg_controllen, and cmsg_len,
+	 * and the cmsg blocks cannot be modified in-place. */
+	int i;
+	if (vlen > IOV_MAX) vlen = IOV_MAX; /* This matches the kernel. */
+	if (!vlen) return 0;
+	for (i=0; i<vlen; i++) {
+		/* As an unfortunate inconsistency, the sendmmsg API uses
+		 * unsigned int for the resulting msg_len, despite sendmsg
+		 * returning ssize_t. However Linux limits the total bytes
+		 * sent by sendmsg to INT_MAX, so the assignment is safe. */
+		ssize_t r = sendmsg(fd, &msgvec[i].msg_hdr, flags);
+		if (r < 0) goto error;
+		msgvec[i].msg_len = r;
+	}
+error:
+	return i ? i : -1;
+#else
+	return syscall_cp(SYS_sendmmsg, fd, msgvec, vlen, flags);
+#endif
+}
-- 
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