Add csum_icmp4() helper for calculating ICMP checksums

Although tap_ip_send() is currently the only place calculating ICMP
checksums, create a helper function for symmetry with ICMPv6.  For
future flexibility it allows the ICMPv6 header and payload to be in
separate buffers.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/checksum.c b/checksum.c
index 78c6960..f35c948 100644
--- a/checksum.c
+++ b/checksum.c
@@ -52,6 +52,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include <linux/icmp.h>
 #include <linux/icmpv6.h>
 
 /**
@@ -108,6 +109,21 @@ uint16_t csum_unaligned(const void *buf, size_t len, uint32_t init)
 }
 
 /**
+ * csum_icmp4() - Calculate and set checksum for an ICMP packet
+ * @icmp4hr:	ICMP header, initialised apart from checksum
+ * @payload:	ICMP packet payload
+ * @len:	Length of @payload (not including ICMP header)
+ */
+void csum_icmp4(struct icmphdr *icmp4hr, const void *payload, size_t len)
+{
+	/* Partial checksum for ICMP header alone */
+	uint32_t psum = sum_16b(icmp4hr, sizeof(*icmp4hr));
+
+	icmp4hr->checksum = 0;
+	icmp4hr->checksum = csum_unaligned(payload, len, psum);
+}
+
+/**
  * csum_icmp6() - Calculate and set checksum for an ICMPv6 packet
  * @icmp6hr:	ICMPv6 header, initialised apart from checksum
  * @saddr:	IPv6 source address