[PATCH bpf-next v3 09/14] selftests/bpf: move ip checksum helper to network helpers

["Alexis Lothoré (eBPF Foundation)" <alexis.lothore@bootlin.com>]

xdp_metadata test has a small helper computing ipv4 checksums to allow
manually building packets.

Move this helper to network_helpers to share it with other tests.

Signed-off-by: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
---
Changes in v3:
- use csum_partial for intermediate helper name to keep sync with the
  corresponding kernel helper
- provide byte count instead of half-word count to csum_partial

Changes in v2:
- new patch
---
 tools/testing/selftests/bpf/network_helpers.h      | 24 ++++++++++++++++++++++
 .../selftests/bpf/prog_tests/xdp_metadata.c        | 19 +----------------
 2 files changed, 25 insertions(+), 18 deletions(-)

diff --git a/tools/testing/selftests/bpf/network_helpers.h b/tools/testing/selftests/bpf/network_helpers.h
index c72c16e1aff825439896b38e59962ffafe92dc71..5ef909f766eb9ac2dd5be67b99245b4676ce4f5f 100644
--- a/tools/testing/selftests/bpf/network_helpers.h
+++ b/tools/testing/selftests/bpf/network_helpers.h
@@ -104,6 +104,30 @@ static __u16 csum_fold(__u32 csum)
 	return (__u16)~csum;
 }
 
+static __wsum csum_partial(const void *buf, int len, __wsum sum)
+{
+	__u16 *p = (__u16 *)buf;
+	int num_u16 = len >> 1;
+	int i;
+
+	for (i = 0; i < num_u16; i++)
+		sum += p[i];
+
+	return sum;
+}
+
+static inline __sum16 build_ip_csum(struct iphdr *iph)
+{
+	__u32 sum = 0;
+	__u16 *p;
+
+	iph->check = 0;
+	p = (void *)iph;
+	sum = csum_partial(p, iph->ihl << 2, 0);
+
+	return csum_fold(sum);
+}
+
 static inline __sum16 csum_tcpudp_magic(__be32 saddr, __be32 daddr,
 					__u32 len, __u8 proto,
 					__wsum csum)
diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c b/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
index c87ee2bf558c1a7fb726cae0aa7b3d3735fb1aac..7f8e161655336127e5bd7a573d1a09db85a92f53 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
@@ -133,23 +133,6 @@ static void close_xsk(struct xsk *xsk)
 	munmap(xsk->umem_area, UMEM_SIZE);
 }
 
-static void ip_csum(struct iphdr *iph)
-{
-	__u32 sum = 0;
-	__u16 *p;
-	int i;
-
-	iph->check = 0;
-	p = (void *)iph;
-	for (i = 0; i < sizeof(*iph) / sizeof(*p); i++)
-		sum += p[i];
-
-	while (sum >> 16)
-		sum = (sum & 0xffff) + (sum >> 16);
-
-	iph->check = ~sum;
-}
-
 static int generate_packet(struct xsk *xsk, __u16 dst_port)
 {
 	struct xsk_tx_metadata *meta;
@@ -192,7 +175,7 @@ static int generate_packet(struct xsk *xsk, __u16 dst_port)
 	iph->protocol = IPPROTO_UDP;
 	ASSERT_EQ(inet_pton(FAMILY, TX_ADDR, &iph->saddr), 1, "inet_pton(TX_ADDR)");
 	ASSERT_EQ(inet_pton(FAMILY, RX_ADDR, &iph->daddr), 1, "inet_pton(RX_ADDR)");
-	ip_csum(iph);
+	iph->check = build_ip_csum(iph);
 
 	udph->source = htons(UDP_SOURCE_PORT);
 	udph->dest = htons(dst_port);

-- 
2.47.0