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dhcp-network: make clear that we are ANDing Fragment offset field with mask

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Reading BPF assembly written as C macros is inherently difficult. Don't
make it harder than necessary and provide clearer explanation in the
comment.
This commit is contained in:
Michal Sekletar 2014-07-07 15:27:24 +02:00
parent b064329fd8
commit ffc90a1196
1 changed files with 1 additions and 1 deletions
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src/libsystemd-network/dhcp-network.c
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@ -46,7 +46,7 @@ int dhcp_network_bind_raw_socket(int index, union sockaddr_union *link,
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 1, 0), /* A == 0 ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(DHCPPacket, ip.frag_off)), /* A <- Flags + Fragment offset */
BPF_STMT(BPF_ALU + BPF_AND + BPF_K, 0x1fff), /* A <- A & 0x1fff */
BPF_STMT(BPF_ALU + BPF_AND + BPF_K, 0x1fff), /* A <- A & 0x1fff (Fragment offset) */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 1, 0), /* A == 0 ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(DHCPPacket, udp.dest)), /* A <- UDP destination port */