apf_csum.h: add alternative checksum implementation
Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <[email protected]>
Change-Id: I046e744b570d6fa7f2a18189a3cb6b17b512b179
diff --git a/apf_checksum.h b/apf_checksum.h
index e6fef6e..34a8524 100644
--- a/apf_checksum.h
+++ b/apf_checksum.h
@@ -86,3 +86,52 @@
default: return 0;
}
}
+
+/**
+ * Calculate and store packet checksums and return dscp.
+ *
+ * @param pkt - pointer to the very start of the to-be-transmitted packet,
+ * ie. the start of the ethernet header (if one is present)
+ * WARNING: at minimum 266 bytes of buffer pointed to by 'pkt' pointer
+ * *MUST* be writable.
+ * (IPv4 header checksum is a 2 byte value, 10 bytes after ip_ofs,
+ * which has a maximum value of 254. Thus 254[ip_ofs] + 10 + 2[u16] = 266)
+ *
+ * @param len - length of the packet (this may be < 266).
+ * @param ip_ofs - offset from beginning of pkt to IPv4 or IPv6 header:
+ * IP version detected based on top nibble of this byte,
+ * for IPv4 we will calculate and store IP header checksum,
+ * but only for the first 20 bytes of the header,
+ * prior to calling this the IPv4 header checksum field
+ * must be initialized to the partial checksum of the IPv4
+ * options (0 if none)
+ * 255 means there is no IP header (for example ARP)
+ * DSCP will be retrieved from this IP header (0 if none).
+ * @param partial_csum - additional value to include in L4 checksum
+ * @param csum_start - offset from beginning of pkt to begin L4 checksum
+ * calculation (until end of pkt specified by len)
+ * @param csum_ofs - offset from beginning of pkt to store L4 checksum
+ * 255 means do not calculate/store L4 checksum
+ * @param udp - true iff we should generate a UDP style L4 checksum (0 -> 0xFFFF)
+ *
+ * @return 6-bit DSCP value [0..63], garbage on parse error.
+ */
+int csum_and_return_dscp(u8* const pkt, const s32 len, const u8 ip_ofs,
+ const u16 partial_csum, const u8 csum_start, const u8 csum_ofs, const bool udp) {
+ if (csum_ofs < 255) {
+ // note that calc_csum() treats negative lengths as zero
+ u32 csum = calc_csum(partial_csum, pkt + csum_start, len - csum_start);
+ if (udp) csum = fix_udp_csum(csum);
+ store_be16(pkt + csum_ofs, csum);
+ }
+ if (ip_ofs < 255) {
+ u8 ip = pkt[ip_ofs] >> 4;
+ if (ip == 4) {
+ store_be16(pkt + ip_ofs + 10, calc_csum(0, pkt + ip_ofs, IPV4_HLEN));
+ return pkt[ip_ofs + 1] >> 2; /* DSCP */
+ } else if (ip == 6) {
+ return (read_be16(pkt + ip_ofs) >> 6) & 0x3F; /* DSCP */
+ }
+ }
+ return 0;
+}
