Add test script for XDP_TX action (#2066)

Mostly a cut and paste of the xdp_drop_count.py with needed changes for
doing a source and destination MAC swap.
Signed-off-by: Andy Gospodarek <gospo@broadcom.com>

examples/networking/xdp/xdp_macswap_count.py

+#!/usr/bin/env python
+#
+# xdp_macswap_count.py Swap Source and Destination MAC addresses on
+#                      incoming packets and transmit packets back on
+#                      same interface in XDP layer and count for which
+#                      protocol type
+#
+# Copyright (c) 2016 PLUMgrid
+# Copyright (c) 2016 Jan Ruth
+# Copyright (c) 2018 Andy Gospodarek
+# Licensed under the Apache License, Version 2.0 (the "License")
+
+from bcc import BPF
+import pyroute2
+import time
+import sys
+
+flags = 0
+def usage():
+    print("Usage: {0} [-S] <ifdev>".format(sys.argv[0]))
+    print("       -S: use skb mode\n")
+    print("e.g.: {0} eth0\n".format(sys.argv[0]))
+    exit(1)
+
+if len(sys.argv) < 2 or len(sys.argv) > 3:
+    usage()
+
+if len(sys.argv) == 2:
+    device = sys.argv[1]
+
+if len(sys.argv) == 3:
+    if "-S" in sys.argv:
+        # XDP_FLAGS_SKB_MODE
+        flags |= 2 << 0
+
+    if "-S" == sys.argv[1]:
+        device = sys.argv[2]
+    else:
+        device = sys.argv[1]
+
+mode = BPF.XDP
+#mode = BPF.SCHED_CLS
+
+if mode == BPF.XDP:
+    ret = "XDP_TX"
+    ctxtype = "xdp_md"
+else:
+    ret = "TC_ACT_SHOT"
+    ctxtype = "__sk_buff"
+
+# load BPF program
+b = BPF(text = """
+#define KBUILD_MODNAME "foo"
+#include <uapi/linux/bpf.h>
+#include <linux/in.h>
+#include <linux/if_ether.h>
+#include <linux/if_packet.h>
+#include <linux/if_vlan.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+
+
+BPF_TABLE("percpu_array", uint32_t, long, dropcnt, 256);
+
+static inline int parse_ipv4(void *data, u64 nh_off, void *data_end) {
+    struct iphdr *iph = data + nh_off;
+
+    if ((void*)&iph[1] > data_end)
+        return 0;
+    return iph->protocol;
+}
+
+static inline int parse_ipv6(void *data, u64 nh_off, void *data_end) {
+    struct ipv6hdr *ip6h = data + nh_off;
+
+    if ((void*)&ip6h[1] > data_end)
+        return 0;
+    return ip6h->nexthdr;
+}
+
+static void swap_src_dst_mac(void *data)
+{
+    unsigned short *p = data;
+    unsigned short dst[3];
+
+    dst[0] = p[0];
+    dst[1] = p[1];
+    dst[2] = p[2];
+    p[0] = p[3];
+    p[1] = p[4];
+    p[2] = p[5];
+    p[3] = dst[0];
+    p[4] = dst[1];
+    p[5] = dst[2];
+}
+
+int xdp_prog1(struct CTXTYPE *ctx) {
+
+    void* data_end = (void*)(long)ctx->data_end;
+    void* data = (void*)(long)ctx->data;
+
+    struct ethhdr *eth = data;
+
+    // drop packets
+    int rc = RETURNCODE; // let pass XDP_PASS or redirect to tx via XDP_TX
+    long *value;
+    uint16_t h_proto;
+    uint64_t nh_off = 0;
+    uint32_t index;
+
+    nh_off = sizeof(*eth);
+
+    if (data + nh_off  > data_end)
+        return rc;
+
+    h_proto = eth->h_proto;
+
+    if (h_proto == htons(ETH_P_8021Q) || h_proto == htons(ETH_P_8021AD)) {
+        struct vlan_hdr *vhdr;
+
+        vhdr = data + nh_off;
+        nh_off += sizeof(struct vlan_hdr);
+        if (data + nh_off > data_end)
+            return rc;
+            h_proto = vhdr->h_vlan_encapsulated_proto;
+    }
+    if (h_proto == htons(ETH_P_8021Q) || h_proto == htons(ETH_P_8021AD)) {
+        struct vlan_hdr *vhdr;
+
+        vhdr = data + nh_off;
+        nh_off += sizeof(struct vlan_hdr);
+        if (data + nh_off > data_end)
+            return rc;
+            h_proto = vhdr->h_vlan_encapsulated_proto;
+    }
+
+    if (h_proto == htons(ETH_P_IP))
+        index = parse_ipv4(data, nh_off, data_end);
+    else if (h_proto == htons(ETH_P_IPV6))
+       index = parse_ipv6(data, nh_off, data_end);
+    else
+        index = 0;
+
+    if (h_proto == IPPROTO_UDP) {
+        swap_src_dst_mac(data);
+        rc = XDP_TX;
+    }
+
+    value = dropcnt.lookup(&index);
+    if (value)
+        *value += 1;
+
+    return rc;
+}
+""", cflags=["-w", "-DRETURNCODE=%s" % ret, "-DCTXTYPE=%s" % ctxtype])
+
+fn = b.load_func("xdp_prog1", mode)
+
+if mode == BPF.XDP:
+    b.attach_xdp(device, fn, flags)
+else:
+    ip = pyroute2.IPRoute()
+    ipdb = pyroute2.IPDB(nl=ip)
+    idx = ipdb.interfaces[device].index
+    ip.tc("add", "clsact", idx)
+    ip.tc("add-filter", "bpf", idx, ":1", fd=fn.fd, name=fn.name,
+          parent="ffff:fff2", classid=1, direct_action=True)
+
+dropcnt = b.get_table("dropcnt")
+prev = [0] * 256
+print("Printing drops per IP protocol-number, hit CTRL+C to stop")
+while 1:
+    try:
+        for k in dropcnt.keys():
+            val = dropcnt.sum(k).value
+            i = k.value
+            if val:
+                delta = val - prev[i]
+                prev[i] = val
+                print("{}: {} pkt/s".format(i, delta))
+        time.sleep(1)
+    except KeyboardInterrupt:
+        print("Removing filter from device")
+        break;
+
+if mode == BPF.XDP:
+    b.remove_xdp(device, flags)
+else:
+    ip.tc("del", "clsact", idx)
+    ipdb.release()