Merge pull request #168 from xdp-project/tutorial32-improve-parsing-r…

…ebase01.public Tutorial improve parsing of VLANs (rebased #73)
xdp-project · Nov 15, 2020 · 9ee02ae · 9ee02ae
2 parents 6d8c0da + 2bb3dbc
commit 9ee02ae
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Showing 2 changed files with 38 additions and 9 deletions.
diff --git a/common/parsing_helpers.h b/common/parsing_helpers.h
@@ -56,9 +56,15 @@ struct icmphdr_common {
 
 /* Allow users of header file to redefine VLAN max depth */
 #ifndef VLAN_MAX_DEPTH
-#define VLAN_MAX_DEPTH 4
+#define VLAN_MAX_DEPTH 2
 #endif
 
+#define VLAN_VID_MASK		0x0fff /* VLAN Identifier */
+/* Struct for collecting VLANs after parsing via parse_ethhdr_vlan */
+struct collect_vlans {
+	__u16 id[VLAN_MAX_DEPTH];
+};
+
 static __always_inline int proto_is_vlan(__u16 h_proto)
 {
 	return !!(h_proto == bpf_htons(ETH_P_8021Q) ||
@@ -70,8 +76,10 @@ static __always_inline int proto_is_vlan(__u16 h_proto)
  * Ethernet header. Thus, caller can look at eth->h_proto to see if this was a
  * VLAN tagged packet.
  */
-static __always_inline int parse_ethhdr(struct hdr_cursor *nh, void *data_end,
-					struct ethhdr **ethhdr)
+static __always_inline int parse_ethhdr_vlan(struct hdr_cursor *nh,
+					     void *data_end,
+					     struct ethhdr **ethhdr,
+					     struct collect_vlans *vlans)
 {
 	struct ethhdr *eth = nh->pos;
 	int hdrsize = sizeof(*eth);
@@ -102,13 +110,25 @@ static __always_inline int parse_ethhdr(struct hdr_cursor *nh, void *data_end,
 			break;
 
 		h_proto = vlh->h_vlan_encapsulated_proto;
+		if (vlans) /* collect VLAN ids */
+			vlans->id[i] =
+				(bpf_ntohs(vlh->h_vlan_TCI) & VLAN_VID_MASK);
+
 		vlh++;
 	}
 
 	nh->pos = vlh;
 	return h_proto; /* network-byte-order */
 }
 
+static __always_inline int parse_ethhdr(struct hdr_cursor *nh,
+					void *data_end,
+					struct ethhdr **ethhdr)
+{
+	/* Expect compiler removes the code that collects VLAN ids */
+	return parse_ethhdr_vlan(nh, data_end, ethhdr, NULL);
+}
+
 static __always_inline int parse_ip6hdr(struct hdr_cursor *nh,
 					void *data_end,
 					struct ipv6hdr **ip6hdr)

diff --git a/packet-solutions/xdp_vlan02_kern.c b/packet-solutions/xdp_vlan02_kern.c
@@ -10,16 +10,19 @@
 #define VLAN_MAX_DEPTH 10
 #include "../common/parsing_helpers.h"
 
+#if 0
 #define VLAN_VID_MASK		0x0fff /* VLAN Identifier */
-struct vlans {
+struct collect_vlans {
 	__u16 id[VLAN_MAX_DEPTH];
 };
+#endif
 
+#if 0 /* moved to parsing_helpers.h */
 /* Based on parse_ethhdr() */
 static __always_inline int __parse_ethhdr_vlan(struct hdr_cursor *nh,
 					       void *data_end,
 					       struct ethhdr **ethhdr,
-					       struct vlans *vlans)
+					       struct collect_vlans *vlans)
 {
 	struct ethhdr *eth = nh->pos;
 	int hdrsize = sizeof(*eth);
@@ -51,14 +54,16 @@ static __always_inline int __parse_ethhdr_vlan(struct hdr_cursor *nh,
 
 		h_proto = vlh->h_vlan_encapsulated_proto;
 		if (vlans) {
-			vlans->id[i] =  vlh->h_vlan_TCI & VLAN_VID_MASK;
+			vlans->id[i] =
+				bpf_ntohs(vlh->h_vlan_TCI) & VLAN_VID_MASK;
 		}
 		vlh++;
 	}
 
 	nh->pos = vlh;
 	return h_proto; /* network-byte-order */
 }
+#endif
 
 SEC("xdp_vlan02")
 int xdp_vlan_02(struct xdp_md *ctx)
@@ -71,13 +76,17 @@ int xdp_vlan_02(struct xdp_md *ctx)
 	int eth_type;
 	nh.pos = data;
 
-	struct vlans vlans;
+	struct collect_vlans vlans;
 
 	struct ethhdr *eth;
-	eth_type = __parse_ethhdr_vlan(&nh, data_end, &eth, &vlans);
 
+	eth_type = parse_ethhdr_vlan(&nh, data_end, &eth, &vlans);
 	if (eth_type < 0)
 		return XDP_ABORTED;
+	/* The eth_type have skipped VLAN-types, but collected VLAN ids. The
+	 * eth ptr still points to Ethernet header, thus to check if this is a
+	 * VLAN packet do proto_is_vlan(eth->h_proto).
+	 */
 
 	/* The LLVM compiler is very clever, it sees that program only access
 	 * 2nd "inner" vlan (array index 1), and only does loop unroll of 2, and
@@ -112,7 +121,7 @@ int xdp_vlan_02(struct xdp_md *ctx)
 	}
 #endif
 	/* Hint: to inspect BPF byte-code run:
-	 *  llvm-objdump -S xdp_vlan02_kern.o
+	 *  llvm-objdump --no-show-raw-insn -S xdp_vlan02_kern.o
 	 */
 	return XDP_PASS;
 }