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authorAlex Elder <elder@linaro.org>2021-06-11 14:05:28 -0500
committerDavid S. Miller <davem@davemloft.net>2021-06-11 13:37:49 -0700
commita2918a169f57f965e4e5949822c2602c90e388ab (patch)
treeab437506c667b66e6ef7952caa6e3564537a9a0a /drivers/net/ethernet/qualcomm/rmnet
parentnet: qualcomm: rmnet: clarify a bit of code (diff)
downloadlinux-dev-a2918a169f57f965e4e5949822c2602c90e388ab.tar.xz
linux-dev-a2918a169f57f965e4e5949822c2602c90e388ab.zip
net: qualcomm: rmnet: avoid unnecessary byte-swapping
Internet checksums are used for IPv4 header checksum, as well as TCP segment and UDP datagram checksums. Such a checksum represents the negated sum of adjacent pairs of bytes, using ones' complement arithmetic. One property of the Internet checkum is byte order independence [1]. Specifically, the sum of byte-swapped pairs is equal to the result of byte swapping the sum of those same pairs when not byte-swapped. So for example if a, b, c, d, y, and z are hexadecimal digits, and PLUS represents ones' complement addition: If: ab PLUS cd = yz Then: ba PLUS dc = zy For this reason, there is no need to swap the order of bytes in the checksum value held in a message header, nor the one in the QMAPv4 trailer, in order to operate on them. In other words, we can determine whether the hardware-computed checksum matches the one in the message header without any byte swaps. (This patch leaves in place all existing type casts.) [1] https://tools.ietf.org/html/rfc1071 Signed-off-by: Alex Elder <elder@linaro.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/net/ethernet/qualcomm/rmnet')
-rw-r--r--drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c8
1 files changed, 4 insertions, 4 deletions
diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
index 4f93355e9a93..39f198d7595b 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -78,15 +78,15 @@ rmnet_map_ipv4_dl_csum_trailer(struct sk_buff *skb,
* trailer checksum. Therefore the checksum in the trailer is
* just the checksum computed over the IP payload.
*/
- ip_payload_csum = (__force __sum16)~ntohs(csum_trailer->csum_value);
+ ip_payload_csum = (__force __sum16)~csum_trailer->csum_value;
pseudo_csum = ~csum_tcpudp_magic(ip4h->saddr, ip4h->daddr,
ntohs(ip4h->tot_len) - ip4h->ihl * 4,
ip4h->protocol, 0);
- addend = (__force __be16)ntohs((__force __be16)pseudo_csum);
+ addend = (__force __be16)pseudo_csum;
pseudo_csum = csum16_add(ip_payload_csum, addend);
- addend = (__force __be16)ntohs((__force __be16)*csum_field);
+ addend = (__force __be16)*csum_field;
csum_temp = ~csum16_sub(pseudo_csum, addend);
csum_value_final = (__force u16)csum_temp;
@@ -105,7 +105,7 @@ rmnet_map_ipv4_dl_csum_trailer(struct sk_buff *skb,
}
}
- if (csum_value_final == ntohs((__force __be16)*csum_field)) {
+ if (csum_value_final == (__force u16)*csum_field) {
priv->stats.csum_ok++;
return 0;
} else {