Subject: [PATCH net-next V6 3/5] selftests: drv-net: Test XDP_TX support

From: Mohsin Bashir <[email-masked]>
Date: Sat, 19 Jul 2025 01:30:57 -0700

Add test to verify the XDP_TX functionality by generating traffic from a
remote node on a specific UDP port and redirecting it back to the sender.

./drivers/net/xdp.py
TAP version 13
1..5
ok 1 xdp.test_xdp_native_pass_sb
ok 2 xdp.test_xdp_native_pass_mb
ok 3 xdp.test_xdp_native_drop_sb
ok 4 xdp.test_xdp_native_drop_mb
ok 5 xdp.test_xdp_native_tx_mb
\# Totals: pass:5 fail:0 xfail:0 xpass:0 skip:0 error:0

Signed-off-by: Jakub Kicinski <[email-masked]>
Signed-off-by: Mohsin Bashir <[email-masked]>
---
 tools/testing/selftests/drivers/net/xdp.py    | 34 ++++++++
 .../selftests/net/lib/xdp_native.bpf.c        | 80 +++++++++++++++++++
 2 files changed, 114 insertions(+)

diff --git a/tools/testing/selftests/drivers/net/xdp.py b/tools/testing/selftests/drivers/net/xdp.py
index 8ab1607edcd8..d42dbee78431 100755
--- a/tools/testing/selftests/drivers/net/xdp.py
+++ b/tools/testing/selftests/drivers/net/xdp.py
@@ -27,6 +27,7 @@ class XDPAction(Enum):
     """Enum for XDP actions."""
     PASS = 0  # Pass the packet up to the stack
     DROP = 1  # Drop the packet
+    TX = 2    # Route the packet to the remote host

 class XDPStats(Enum):
@@ -34,6 +35,7 @@ class XDPStats(Enum):
     RX = 0    # Count of valid packets received for testing
     PASS = 1  # Count of packets passed up to the stack
     DROP = 2  # Count of packets dropped
+    TX = 3    # Count of incoming packets routed to the remote host

 @dataclass
@@ -180,6 +182,8 @@ def _get_stats(xdp_map_id):
             stats_formatted[XDPStats.PASS.value] = val
         elif stats_dump[key]["formatted"]["key"] == XDPStats.DROP.value:
             stats_formatted[XDPStats.DROP.value] = val
+        elif stats_dump[key]["formatted"]["key"] == XDPStats.TX.value:
+            stats_formatted[XDPStats.TX.value] = val
 
     return stats_formatted
 
@@ -278,6 +282,35 @@ def test_xdp_native_drop_mb(cfg):
     _test_drop(cfg, bpf_info, 8000)

+def test_xdp_native_tx_mb(cfg):
+    """
+    Tests the XDP_TX action for a multi-buff case.
+
+    Args:
+        cfg: Configuration object containing network settings.
+    """
+    cfg.require_cmd("socat", remote=True)
+
+    bpf_info = BPFProgInfo("xdp_prog_frags", "xdp_native.bpf.o", "xdp.frags", 9000)
+    prog_info = _load_xdp_prog(cfg, bpf_info)
+    port = rand_port()
+
+    _set_xdp_map("map_xdp_setup", TestConfig.MODE.value, XDPAction.TX.value)
+    _set_xdp_map("map_xdp_setup", TestConfig.PORT.value, port)
+
+    test_string = ''.join(random.choice(string.ascii_lowercase) for _ in range(8000))
+    rx_udp = f"socat -{cfg.addr_ipver} -T 2 -u UDP-RECV:{port},reuseport STDOUT"
+    tx_udp = f"echo {test_string} | socat -t 2 -u STDIN UDP:{cfg.baddr}:{port}"
+
+    with bkg(rx_udp, host=cfg.remote, exit_wait=True) as rnc:
+        cmd(tx_udp, host=cfg.remote, shell=True)
+
+    stats = _get_stats(prog_info['maps']['map_xdp_stats'])
+
+    ksft_eq(rnc.stdout.strip(), test_string, "UDP packet exchange failed")
+    ksft_eq(stats[XDPStats.TX.value], 1, "TX stats mismatch")
+
+
 def main():
     """
     Main function to execute the XDP tests.
@@ -294,6 +327,7 @@ def main():
                 test_xdp_native_pass_mb,
                 test_xdp_native_drop_sb,
                 test_xdp_native_drop_mb,
+                test_xdp_native_tx_mb,
             ],
             args=(cfg,))
     ksft_exit()
diff --git a/tools/testing/selftests/net/lib/xdp_native.bpf.c b/tools/testing/selftests/net/lib/xdp_native.bpf.c
index 90b34b2a4fef..d3c66c891589 100644
--- a/tools/testing/selftests/net/lib/xdp_native.bpf.c
+++ b/tools/testing/selftests/net/lib/xdp_native.bpf.c
@@ -18,12 +18,14 @@ enum {
 enum {
 	XDP_MODE_PASS = 0,
 	XDP_MODE_DROP = 1,
+	XDP_MODE_TX = 2,
 } xdp_map_modes;
 
 enum {
 	STATS_RX = 0,
 	STATS_PASS = 1,
 	STATS_DROP = 2,
+	STATS_TX = 3,
 } xdp_stats;
 
 struct {
@@ -117,6 +119,82 @@ static int xdp_mode_drop_handler(struct xdp_md *ctx, __u16 port)
 	return XDP_DROP;
 }
 
+static void swap_machdr(void *data)
+{
+	struct ethhdr *eth = data;
+	__u8 tmp_mac[ETH_ALEN];
+
+	__builtin_memcpy(tmp_mac, eth->h_source, ETH_ALEN);
+	__builtin_memcpy(eth->h_source, eth->h_dest, ETH_ALEN);
+	__builtin_memcpy(eth->h_dest, tmp_mac, ETH_ALEN);
+}
+
+static int xdp_mode_tx_handler(struct xdp_md *ctx, __u16 port)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+	struct udphdr *udph = NULL;
+	struct ethhdr *eth = data;
+
+	if (data + sizeof(*eth) > data_end)
+		return XDP_PASS;
+
+	if (eth->h_proto == bpf_htons(ETH_P_IP)) {
+		struct iphdr *iph = data + sizeof(*eth);
+		__be32 tmp_ip = iph->saddr;
+
+		if (iph + 1 > (struct iphdr *)data_end ||
+		    iph->protocol != IPPROTO_UDP)
+			return XDP_PASS;
+
+		udph = data + sizeof(*iph) + sizeof(*eth);
+
+		if (udph + 1 > (struct udphdr *)data_end)
+			return XDP_PASS;
+		if (udph->dest != bpf_htons(port))
+			return XDP_PASS;
+
+		record_stats(ctx, STATS_RX);
+		swap_machdr((void *)eth);
+
+		iph->saddr = iph->daddr;
+		iph->daddr = tmp_ip;
+
+		record_stats(ctx, STATS_TX);
+
+		return XDP_TX;
+
+	} else if (eth->h_proto  == bpf_htons(ETH_P_IPV6)) {
+		struct ipv6hdr *ipv6h = data + sizeof(*eth);
+		struct in6_addr tmp_ipv6;
+
+		if (ipv6h + 1 > (struct ipv6hdr *)data_end ||
+		    ipv6h->nexthdr != IPPROTO_UDP)
+			return XDP_PASS;
+
+		udph = data + sizeof(*ipv6h) + sizeof(*eth);
+
+		if (udph + 1 > (struct udphdr *)data_end)
+			return XDP_PASS;
+		if (udph->dest != bpf_htons(port))
+			return XDP_PASS;
+
+		record_stats(ctx, STATS_RX);
+		swap_machdr((void *)eth);
+
+		__builtin_memcpy(&tmp_ipv6, &ipv6h->saddr, sizeof(tmp_ipv6));
+		__builtin_memcpy(&ipv6h->saddr, &ipv6h->daddr,
+				 sizeof(tmp_ipv6));
+		__builtin_memcpy(&ipv6h->daddr, &tmp_ipv6, sizeof(tmp_ipv6));
+
+		record_stats(ctx, STATS_TX);
+
+		return XDP_TX;
+	}
+
+	return XDP_PASS;
+}
+
 static int xdp_prog_common(struct xdp_md *ctx)
 {
 	__u32 key, *port;
@@ -137,6 +215,8 @@ static int xdp_prog_common(struct xdp_md *ctx)
 		return xdp_mode_pass(ctx, (__u16)(*port));
 	case XDP_MODE_DROP:
 		return xdp_mode_drop_handler(ctx, (__u16)(*port));
+	case XDP_MODE_TX:
+		return xdp_mode_tx_handler(ctx, (__u16)(*port));
 	}
 
 	/* Default action is to simple pass */
-- 
2.47.1