From 2ad7561f9f658f8dee168a76654c7d918e2260c7 Mon Sep 17 00:00:00 2001 From: Tom Gundersen Date: Sun, 30 Mar 2014 20:36:44 +0200 Subject: [PATCH] sd-dhcp: avoid checksum calculation if possible When receiving lots of packets that are not meant for us, we waste a relatively large amount of cpu time computing their checksums before discarding them. Move the checksum calculation last so we never compute it for packets which would otherwise be discarded. --- src/libsystemd-network/dhcp-packet.c | 28 ++++++++++++++++------------ 1 file changed, 16 insertions(+), 12 deletions(-) diff --git a/src/libsystemd-network/dhcp-packet.c b/src/libsystemd-network/dhcp-packet.c index 3b62c2572..4f90c283a 100644 --- a/src/libsystemd-network/dhcp-packet.c +++ b/src/libsystemd-network/dhcp-packet.c @@ -155,11 +155,6 @@ int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) { return -EINVAL; } - if (dhcp_packet_checksum(&packet->ip, hdrlen)) { - log_dhcp_client(client, "ignoring packet: invalid IP checksum"); - return -EINVAL; - } - /* UDP */ if (packet->ip.protocol != IPPROTO_UDP) { @@ -181,6 +176,22 @@ int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) { return -EINVAL; } + if (be16toh(packet->udp.dest) != DHCP_PORT_CLIENT) { + log_dhcp_client(client, "ignoring packet: to port %u, which " + "is not the DHCP client port (%u)", + be16toh(packet->udp.dest), DHCP_PORT_CLIENT); + return -EINVAL; + } + + /* checksums - computing these is relatively expensive, so only do it + if all the other checks have passed + */ + + if (dhcp_packet_checksum(&packet->ip, hdrlen)) { + log_dhcp_client(client, "ignoring packet: invalid IP checksum"); + return -EINVAL; + } + if (checksum && packet->udp.check) { packet->ip.check = packet->udp.len; packet->ip.ttl = 0; @@ -192,12 +203,5 @@ int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) { } } - if (be16toh(packet->udp.dest) != DHCP_PORT_CLIENT) { - log_dhcp_client(client, "ignoring packet: to port %u, which " - "is not the DHCP client port (%u)", - be16toh(packet->udp.dest), DHCP_PORT_CLIENT); - return -EINVAL; - } - return 0; } -- 2.30.2