merd: ARP and DHCP handlers, connection tracking fixes

With this, merd provides a fully functional IPv4 environment to
guests, requiring a single capability, CAP_NET_RAW.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/util.c b/util.c
new file mode 100644
index 0000000..23eccb1
--- /dev/null
+++ b/util.c
@@ -0,0 +1,48 @@
+/* MERD - MacVTap Egress and Routing Daemon
+ *
+ * util.c - Convenience helpers
+ *
+ * Author: Stefano Brivio <sbrivio@redhat.com>
+ * License: GPLv2
+ *
+ */
+
+#include <stdint.h>
+#include <stddef.h>
+
+/**
+ * csum_fold() - Fold long sum for IP and TCP checksum
+ * @sum:	Original long sum
+ *
+ * Return: 16-bit folded sum
+ */
+uint16_t csum_fold(uint32_t sum)
+{
+	while (sum >> 16)
+		sum = (sum & 0xffff) + (sum >> 16);
+
+	return sum;
+}
+
+/**
+ * csum_ipv4() - Calculate IPv4 checksum
+ * @buf:	Packet buffer, L3 headers
+ * @len:	Total L3 packet length
+ *
+ * Return: 16-bit IPv4-style checksum
+ */
+uint16_t csum_ip4(void *buf, size_t len)
+{
+	uint32_t sum = 0;
+	uint16_t *p = buf;
+	size_t len1 = len / 2;
+	size_t off;
+
+	for (off = 0; off < len1; off++, p++)
+		sum += *p;
+
+	if (len % 2)
+		sum += *p & 0xff;
+
+	return ~csum_fold(sum);
+}