From: Alex Elder <elder@linaro.org>
To: subashab@codeaurora.org, stranche@codeaurora.org,
davem@davemloft.net, kuba@kernel.org
Cc: bjorn.andersson@linaro.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: [PATCH net-next 3/8] net: qualcomm: rmnet: show that an intermediate sum is zero
Date: Sat, 12 Jun 2021 09:37:31 -0500 [thread overview]
Message-ID: <20210612143736.3498712-4-elder@linaro.org> (raw)
In-Reply-To: <20210612143736.3498712-1-elder@linaro.org>
This patch simply demonstrates that a checksum value computed when
verifying an offloaded transport checksum value for both IPv4 and
IPv6 is (normally) 0. It can be squashed into the next patch.
Signed-off-by: Alex Elder <elder@linaro.org>
---
drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
index 1b170e9189d8a..51909b8fa8a80 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -84,6 +84,11 @@ rmnet_map_ipv4_dl_csum_trailer(struct sk_buff *skb,
ip4h->protocol, 0);
pseudo_csum = csum16_add(ip_payload_csum, (__force __be16)pseudo_csum);
+ /* The trailer checksum *includes* the checksum in the transport
+ * header. Adding that to the pseudo checksum will yield 0xffff
+ * ("negative 0") if the message arrived intact.
+ */
+ WARN_ON((__sum16)~pseudo_csum);
csum_value_final = ~csum16_sub(pseudo_csum, (__force __be16)*csum_field);
if (unlikely(!csum_value_final)) {
@@ -150,6 +155,10 @@ rmnet_map_ipv6_dl_csum_trailer(struct sk_buff *skb,
length, ip6h->nexthdr, 0);
pseudo_csum = csum16_add(ip6_payload_csum, (__force __be16)pseudo_csum);
+ /* Adding the payload checksum to the pseudo checksum yields 0xffff
+ * ("negative 0") if the message arrived intact.
+ */
+ WARN_ON((__sum16)~pseudo_csum);
csum_value_final = ~csum16_sub(pseudo_csum, (__force __be16)*csum_field);
if (unlikely(csum_value_final == 0)) {
--
2.27.0
next prev parent reply other threads:[~2021-06-12 14:39 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-12 14:37 [PATCH net-next 0/8] net: qualcomm: rmnet: MAPv4 download checksum cleanup, part 2 Alex Elder
2021-06-12 14:37 ` [PATCH net-next 1/8] net: qualcomm: rmnet: remove some local variables Alex Elder
2021-06-12 14:37 ` [PATCH net-next 2/8] net: qualcomm: rmnet: rearrange some NOTs Alex Elder
2021-06-12 14:37 ` Alex Elder [this message]
2021-06-12 14:37 ` [PATCH net-next 4/8] net: qualcomm: rmnet: return earlier for bad checksum Alex Elder
2021-06-12 14:37 ` [PATCH net-next 5/8] net: qualcomm: rmnet: remove unneeded code Alex Elder
2021-06-12 14:37 ` [PATCH net-next 6/8] net: qualcomm: rmnet: trailer value is a checksum Alex Elder
2021-06-12 14:37 ` [PATCH net-next 7/8] net: qualcomm: rmnet: drop some unary NOTs Alex Elder
2021-06-12 14:37 ` [PATCH net-next 8/8] net: qualcomm: rmnet: IPv6 payload length is simple Alex Elder
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