Merge branch 'XDP-redirect-tracepoints'

Jesper Dangaard Brouer says:

====================
XDP redirect tracepoints

I feel this is as far as I can take the tracepoint infrastructure to
assist XDP monitoring.

Tracepoints comes with a base overhead of 25 nanosec for an attached
bpf_prog, and 48 nanosec for using a full perf record. This is
problematic for the XDP use-case, but it is very convenient to use the
existing perf infrastructure.

From a performance perspective, the real solution would be to attach
another bpf_prog (that understand xdp_buff), but I'm not sure we want
to introduce yet another bpf attach API for this.

One thing left is to standardize the possible err return codes, to a
limited set, to allow easier (and faster) mapping into a bpf map.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

include/trace/events/xdp.h

@@ -31,55 +31,119 @@ TRACE_EVENT(xdp_exception,
 	TP_ARGS(dev, xdp, act),
 
 	TP_STRUCT__entry(
-		__array(u8, prog_tag, 8)
+		__field(int, prog_id)
 		__field(u32, act)
 		__field(int, ifindex)
 	),
 
 	TP_fast_assign(
-		BUILD_BUG_ON(sizeof(__entry->prog_tag) != sizeof(xdp->tag));
-		memcpy(__entry->prog_tag, xdp->tag, sizeof(xdp->tag));
+		__entry->prog_id	= xdp->aux->id;
 		__entry->act		= act;
 		__entry->ifindex	= dev->ifindex;
 	),
 
-	TP_printk("prog=%s action=%s ifindex=%d",
-		  __print_hex_str(__entry->prog_tag, 8),
+	TP_printk("prog_id=%d action=%s ifindex=%d",
+		  __entry->prog_id,
 		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
 		  __entry->ifindex)
 );
 
-TRACE_EVENT(xdp_redirect,
+DECLARE_EVENT_CLASS(xdp_redirect_template,
 
 	TP_PROTO(const struct net_device *dev,
-		 const struct bpf_prog *xdp, u32 act,
-		 int to_index, int err),
+		 const struct bpf_prog *xdp,
+		 int to_ifindex, int err,
+		 const struct bpf_map *map, u32 map_index),
 
-	TP_ARGS(dev, xdp, act, to_index, err),
+	TP_ARGS(dev, xdp, to_ifindex, err, map, map_index),
 
 	TP_STRUCT__entry(
-		__array(u8, prog_tag, 8)
+		__field(int, prog_id)
 		__field(u32, act)
 		__field(int, ifindex)
-		__field(int, to_index)
 		__field(int, err)
+		__field(int, to_ifindex)
+		__field(u32, map_id)
+		__field(int, map_index)
 	),
 
 	TP_fast_assign(
-		BUILD_BUG_ON(sizeof(__entry->prog_tag) != sizeof(xdp->tag));
-		memcpy(__entry->prog_tag, xdp->tag, sizeof(xdp->tag));
-		__entry->act		= act;
+		__entry->prog_id	= xdp->aux->id;
+		__entry->act		= XDP_REDIRECT;
 		__entry->ifindex	= dev->ifindex;
-		__entry->to_index	= to_index;
 		__entry->err		= err;
+		__entry->to_ifindex	= to_ifindex;
+		__entry->map_id		= map ? map->id : 0;
+		__entry->map_index	= map_index;
 	),
 
-	TP_printk("prog=%s action=%s ifindex=%d to_index=%d err=%d",
-		  __print_hex_str(__entry->prog_tag, 8),
+	TP_printk("prog_id=%d action=%s ifindex=%d to_ifindex=%d err=%d",
+		  __entry->prog_id,
 		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
-		  __entry->ifindex, __entry->to_index,
+		  __entry->ifindex, __entry->to_ifindex,
 		  __entry->err)
 );
+
+DEFINE_EVENT(xdp_redirect_template, xdp_redirect,
+	TP_PROTO(const struct net_device *dev,
+		 const struct bpf_prog *xdp,
+		 int to_ifindex, int err,
+		 const struct bpf_map *map, u32 map_index),
+	TP_ARGS(dev, xdp, to_ifindex, err, map, map_index)
+);
+
+DEFINE_EVENT(xdp_redirect_template, xdp_redirect_err,
+	TP_PROTO(const struct net_device *dev,
+		 const struct bpf_prog *xdp,
+		 int to_ifindex, int err,
+		 const struct bpf_map *map, u32 map_index),
+	TP_ARGS(dev, xdp, to_ifindex, err, map, map_index)
+);
+
+#define _trace_xdp_redirect(dev, xdp, to)		\
+	 trace_xdp_redirect(dev, xdp, to, 0, NULL, 0);
+
+#define _trace_xdp_redirect_err(dev, xdp, to, err)	\
+	 trace_xdp_redirect_err(dev, xdp, to, err, NULL, 0);
+
+DEFINE_EVENT_PRINT(xdp_redirect_template, xdp_redirect_map,
+	TP_PROTO(const struct net_device *dev,
+		 const struct bpf_prog *xdp,
+		 int to_ifindex, int err,
+		 const struct bpf_map *map, u32 map_index),
+	TP_ARGS(dev, xdp, to_ifindex, err, map, map_index),
+	TP_printk("prog_id=%d action=%s ifindex=%d to_ifindex=%d err=%d"
+		  " map_id=%d map_index=%d",
+		  __entry->prog_id,
+		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
+		  __entry->ifindex, __entry->to_ifindex,
+		  __entry->err,
+		  __entry->map_id, __entry->map_index)
+);
+
+DEFINE_EVENT_PRINT(xdp_redirect_template, xdp_redirect_map_err,
+	TP_PROTO(const struct net_device *dev,
+		 const struct bpf_prog *xdp,
+		 int to_ifindex, int err,
+		 const struct bpf_map *map, u32 map_index),
+	TP_ARGS(dev, xdp, to_ifindex, err, map, map_index),
+	TP_printk("prog_id=%d action=%s ifindex=%d to_ifindex=%d err=%d"
+		  " map_id=%d map_index=%d",
+		  __entry->prog_id,
+		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
+		  __entry->ifindex, __entry->to_ifindex,
+		  __entry->err,
+		  __entry->map_id, __entry->map_index)
+);
+
+#define _trace_xdp_redirect_map(dev, xdp, fwd, map, idx)		\
+	 trace_xdp_redirect_map(dev, xdp, fwd ? fwd->ifindex : 0,	\
+				0, map, idx);
+
+#define _trace_xdp_redirect_map_err(dev, xdp, fwd, map, idx, err)	\
+	 trace_xdp_redirect_map_err(dev, xdp, fwd ? fwd->ifindex : 0,	\
+				    err, map, idx);
+
 #endif /* _TRACE_XDP_H */
 
 #include <trace/define_trace.h>

net/core/filter.c

@@ -2515,16 +2515,20 @@ static int xdp_do_redirect_map(struct net_device *dev, struct xdp_buff *xdp,
 	fwd = __dev_map_lookup_elem(map, index);
 	if (!fwd) {
 		err = -EINVAL;
-		goto out;
+		goto err;
 	}
 	if (ri->map_to_flush && ri->map_to_flush != map)
 		xdp_do_flush_map();
 
 	err = __bpf_tx_xdp(fwd, map, xdp, index);
-	if (likely(!err))
-		ri->map_to_flush = map;
-out:
-	trace_xdp_redirect(dev, xdp_prog, XDP_REDIRECT, index, err);
+	if (unlikely(err))
+		goto err;
+
+	ri->map_to_flush = map;
+	_trace_xdp_redirect_map(dev, xdp_prog, fwd, map, index);
+	return 0;
+err:
+	_trace_xdp_redirect_map_err(dev, xdp_prog, fwd, map, index, err);
 	return err;
 }
 
@@ -2543,12 +2547,17 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
 	ri->ifindex = 0;
 	if (unlikely(!fwd)) {
 		err = -EINVAL;
-		goto out;
+		goto err;
 	}
 
 	err = __bpf_tx_xdp(fwd, NULL, xdp, 0);
-out:
-	trace_xdp_redirect(dev, xdp_prog, XDP_REDIRECT, index, err);
+	if (unlikely(err))
+		goto err;
+
+	_trace_xdp_redirect(dev, xdp_prog, index);
+	return 0;
+err:
+	_trace_xdp_redirect_err(dev, xdp_prog, index, err);
 	return err;
 }
 EXPORT_SYMBOL_GPL(xdp_do_redirect);
@@ -2566,23 +2575,25 @@ int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb,
 	ri->ifindex = 0;
 	if (unlikely(!fwd)) {
 		err = -EINVAL;
-		goto out;
+		goto err;
 	}
 
 	if (unlikely(!(fwd->flags & IFF_UP))) {
 		err = -ENETDOWN;
-		goto out;
+		goto err;
 	}
 
 	len = fwd->mtu + fwd->hard_header_len + VLAN_HLEN;
 	if (skb->len > len) {
 		err = -EMSGSIZE;
-		goto out;
+		goto err;
 	}
 
 	skb->dev = fwd;
-out:
-	trace_xdp_redirect(dev, xdp_prog, XDP_REDIRECT, index, err);
+	_trace_xdp_redirect(dev, xdp_prog, index);
+	return 0;
+err:
+	_trace_xdp_redirect_err(dev, xdp_prog, index, err);
 	return err;
 }
 EXPORT_SYMBOL_GPL(xdp_do_generic_redirect);

samples/bpf/Makefile

@@ -39,6 +39,7 @@ hostprogs-y += per_socket_stats_example
 hostprogs-y += load_sock_ops
 hostprogs-y += xdp_redirect
 hostprogs-y += xdp_redirect_map
+hostprogs-y += xdp_monitor
 hostprogs-y += syscall_tp
 
 # Libbpf dependencies
@@ -83,6 +84,7 @@ test_map_in_map-objs := bpf_load.o $(LIBBPF) test_map_in_map_user.o
 per_socket_stats_example-objs := $(LIBBPF) cookie_uid_helper_example.o
 xdp_redirect-objs := bpf_load.o $(LIBBPF) xdp_redirect_user.o
 xdp_redirect_map-objs := bpf_load.o $(LIBBPF) xdp_redirect_map_user.o
+xdp_monitor-objs := bpf_load.o $(LIBBPF) xdp_monitor_user.o
 syscall_tp-objs := bpf_load.o $(LIBBPF) syscall_tp_user.o
 
 # Tell kbuild to always build the programs
@@ -127,6 +129,7 @@ always += tcp_iw_kern.o
 always += tcp_clamp_kern.o
 always += xdp_redirect_kern.o
 always += xdp_redirect_map_kern.o
+always += xdp_monitor_kern.o
 always += syscall_tp_kern.o
 
 HOSTCFLAGS += -I$(objtree)/usr/include
@@ -166,6 +169,7 @@ HOSTLOADLIBES_xdp_tx_iptunnel += -lelf
 HOSTLOADLIBES_test_map_in_map += -lelf
 HOSTLOADLIBES_xdp_redirect += -lelf
 HOSTLOADLIBES_xdp_redirect_map += -lelf
+HOSTLOADLIBES_xdp_monitor += -lelf
 HOSTLOADLIBES_syscall_tp += -lelf
 
 # Allows pointing LLC/CLANG to a LLVM backend with bpf support, redefine on cmdline:

samples/bpf/xdp_monitor_kern.c

@@ -0,0 +1,88 @@
+/* XDP monitor tool, based on tracepoints
+ *
+ *  Copyright(c) 2017 Jesper Dangaard Brouer, Red Hat Inc.
+ */
+#include <uapi/linux/bpf.h>
+#include "bpf_helpers.h"
+
+struct bpf_map_def SEC("maps") redirect_err_cnt = {
+	.type = BPF_MAP_TYPE_PERCPU_ARRAY,
+	.key_size = sizeof(u32),
+	.value_size = sizeof(u64),
+	.max_entries = 2,
+	/* TODO: have entries for all possible errno's */
+};
+
+/* Tracepoint format: /sys/kernel/debug/tracing/events/xdp/xdp_redirect/format
+ * Code in:                kernel/include/trace/events/xdp.h
+ */
+struct xdp_redirect_ctx {
+	unsigned short common_type;	//	offset:0;  size:2; signed:0;
+	unsigned char common_flags;	//	offset:2;  size:1; signed:0;
+	unsigned char common_preempt_count;//	offset:3;  size:1; signed:0;
+	int common_pid;			//	offset:4;  size:4; signed:1;
+
+	int prog_id;			//	offset:8;  size:4; signed:1;
+	u32 act;			//	offset:12  size:4; signed:0;
+	int ifindex;			//	offset:16  size:4; signed:1;
+	int err;			//	offset:20  size:4; signed:1;
+	int to_ifindex;			//	offset:24  size:4; signed:1;
+	u32 map_id;			//	offset:28  size:4; signed:0;
+	int map_index;			//	offset:32  size:4; signed:1;
+};					//	offset:36
+
+enum {
+	XDP_REDIRECT_SUCCESS = 0,
+	XDP_REDIRECT_ERROR = 1
+};
+
+static __always_inline
+int xdp_redirect_collect_stat(struct xdp_redirect_ctx *ctx)
+{
+	u32 key = XDP_REDIRECT_ERROR;
+	int err = ctx->err;
+	u64 *cnt;
+
+	if (!err)
+		key = XDP_REDIRECT_SUCCESS;
+
+	cnt  = bpf_map_lookup_elem(&redirect_err_cnt, &key);
+	if (!cnt)
+		return 0;
+	*cnt += 1;
+
+	return 0; /* Indicate event was filtered (no further processing)*/
+	/*
+	 * Returning 1 here would allow e.g. a perf-record tracepoint
+	 * to see and record these events, but it doesn't work well
+	 * in-practice as stopping perf-record also unload this
+	 * bpf_prog.  Plus, there is additional overhead of doing so.
+	 */
+}
+
+SEC("tracepoint/xdp/xdp_redirect_err")
+int trace_xdp_redirect_err(struct xdp_redirect_ctx *ctx)
+{
+	return xdp_redirect_collect_stat(ctx);
+}
+
+
+SEC("tracepoint/xdp/xdp_redirect_map_err")
+int trace_xdp_redirect_map_err(struct xdp_redirect_ctx *ctx)
+{
+	return xdp_redirect_collect_stat(ctx);
+}
+
+/* Likely unloaded when prog starts */
+SEC("tracepoint/xdp/xdp_redirect")
+int trace_xdp_redirect(struct xdp_redirect_ctx *ctx)
+{
+	return xdp_redirect_collect_stat(ctx);
+}
+
+/* Likely unloaded when prog starts */
+SEC("tracepoint/xdp/xdp_redirect_map")
+int trace_xdp_redirect_map(struct xdp_redirect_ctx *ctx)
+{
+	return xdp_redirect_collect_stat(ctx);
+}

samples/bpf/xdp_monitor_user.c

@@ -0,0 +1,295 @@
+/* Copyright(c) 2017 Jesper Dangaard Brouer, Red Hat, Inc.
+ */
+static const char *__doc__=
+ "XDP monitor tool, based on tracepoints\n"
+;
+
+static const char *__doc_err_only__=
+ " NOTICE: Only tracking XDP redirect errors\n"
+ "         Enable TX success stats via '--stats'\n"
+ "         (which comes with a per packet processing overhead)\n"
+;
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+#include <ctype.h>
+#include <unistd.h>
+#include <locale.h>
+
+#include <getopt.h>
+#include <net/if.h>
+#include <time.h>
+
+#include "libbpf.h"
+#include "bpf_load.h"
+#include "bpf_util.h"
+
+static int verbose = 1;
+static bool debug = false;
+
+static const struct option long_options[] = {
+	{"help",	no_argument,		NULL, 'h' },
+	{"debug",	no_argument,		NULL, 'D' },
+	{"stats",	no_argument,		NULL, 'S' },
+	{"sec", 	required_argument,	NULL, 's' },
+	{0, 0, NULL,  0 }
+};
+
+static void usage(char *argv[])
+{
+	int i;
+	printf("\nDOCUMENTATION:\n%s\n", __doc__);
+	printf("\n");
+	printf(" Usage: %s (options-see-below)\n",
+	       argv[0]);
+	printf(" Listing options:\n");
+	for (i = 0; long_options[i].name != 0; i++) {
+		printf(" --%-15s", long_options[i].name);
+		if (long_options[i].flag != NULL)
+			printf(" flag (internal value:%d)",
+			       *long_options[i].flag);
+		else
+			printf("(internal short-option: -%c)",
+			       long_options[i].val);
+		printf("\n");
+	}
+	printf("\n");
+}
+
+#define NANOSEC_PER_SEC 1000000000 /* 10^9 */
+__u64 gettime(void)
+{
+	struct timespec t;
+	int res;
+
+	res = clock_gettime(CLOCK_MONOTONIC, &t);
+	if (res < 0) {
+		fprintf(stderr, "Error with gettimeofday! (%i)\n", res);
+		exit(EXIT_FAILURE);
+	}
+	return (__u64) t.tv_sec * NANOSEC_PER_SEC + t.tv_nsec;
+}
+
+enum {
+	REDIR_SUCCESS = 0,
+	REDIR_ERROR = 1,
+};
+#define REDIR_RES_MAX 2
+static const char *redir_names[REDIR_RES_MAX] = {
+	[REDIR_SUCCESS]	= "Success",
+	[REDIR_ERROR]	= "Error",
+};
+static const char *err2str(int err)
+{
+	if (err < REDIR_RES_MAX)
+		return redir_names[err];
+	return NULL;
+}
+
+struct record {
+	__u64 counter;
+	__u64 timestamp;
+};
+
+struct stats_record {
+	struct record xdp_redir[REDIR_RES_MAX];
+};
+
+static void stats_print_headers(bool err_only)
+{
+	if (err_only)
+		printf("\n%s\n", __doc_err_only__);
+
+	printf("%-14s %-10s %-18s %-9s\n",
+	       "XDP_REDIRECT", "pps ", "pps-human-readable", "measure-period");
+}
+
+static void stats_print(struct stats_record *rec,
+			struct stats_record *prev,
+			bool err_only)
+{
+	int i = 0;
+
+	if (err_only)
+		i = REDIR_ERROR;
+
+	for (; i < REDIR_RES_MAX; i++) {
+		struct record *r = &rec->xdp_redir[i];
+		struct record *p = &prev->xdp_redir[i];
+		__u64 period  = 0;
+		__u64 packets = 0;
+		double pps = 0;
+		double period_ = 0;
+
+		if (p->timestamp) {
+			packets = r->counter - p->counter;
+			period  = r->timestamp - p->timestamp;
+			if (period > 0) {
+				period_ = ((double) period / NANOSEC_PER_SEC);
+				pps = packets / period_;
+			}
+		}
+
+		printf("%-14s %-10.0f %'-18.0f %f\n",
+		       err2str(i), pps, pps, period_);
+	}
+}
+
+static __u64 get_key32_value64_percpu(int fd, __u32 key)
+{
+	/* For percpu maps, userspace gets a value per possible CPU */
+	unsigned int nr_cpus = bpf_num_possible_cpus();
+	__u64 values[nr_cpus];
+	__u64 sum = 0;
+	int i;
+
+	if ((bpf_map_lookup_elem(fd, &key, values)) != 0) {
+		fprintf(stderr,
+			"ERR: bpf_map_lookup_elem failed key:0x%X\n", key);
+		return 0;
+	}
+
+	/* Sum values from each CPU */
+	for (i = 0; i < nr_cpus; i++) {
+		sum += values[i];
+	}
+	return sum;
+}
+
+static bool stats_collect(int fd, struct stats_record *rec)
+{
+	int i;
+
+	/* TODO: Detect if someone unloaded the perf event_fd's, as
+	 * this can happen by someone running perf-record -e
+	 */
+
+	for (i = 0; i < REDIR_RES_MAX; i++) {
+		rec->xdp_redir[i].timestamp = gettime();
+		rec->xdp_redir[i].counter = get_key32_value64_percpu(fd, i);
+	}
+	return true;
+}
+
+static void stats_poll(int interval, bool err_only)
+{
+	struct stats_record rec, prev;
+	int map_fd;
+
+	memset(&rec, 0, sizeof(rec));
+
+	/* Trick to pretty printf with thousands separators use %' */
+	setlocale(LC_NUMERIC, "en_US");
+
+	/* Header */
+	if (verbose)
+		printf("\n%s", __doc__);
+
+	/* TODO Need more advanced stats on error types */
+	if (verbose)
+		printf(" - Stats map: %s\n", map_data[0].name);
+	map_fd = map_data[0].fd;
+
+	stats_print_headers(err_only);
+	fflush(stdout);
+
+	while (1) {
+		memcpy(&prev, &rec, sizeof(rec));
+		stats_collect(map_fd, &rec);
+		stats_print(&rec, &prev, err_only);
+		fflush(stdout);
+		sleep(interval);
+	}
+}
+
+void print_bpf_prog_info(void)
+{
+	int i;
+
+	/* Prog info */
+	printf("Loaded BPF prog have %d bpf program(s)\n", prog_cnt);
+	for (i = 0; i < prog_cnt; i++) {
+		printf(" - prog_fd[%d] = fd(%d)\n", i, prog_fd[i]);
+	}
+
+	/* Maps info */
+	printf("Loaded BPF prog have %d map(s)\n", map_data_count);
+	for (i = 0; i < map_data_count; i++) {
+		char *name = map_data[i].name;
+		int fd     = map_data[i].fd;
+
+		printf(" - map_data[%d] = fd(%d) name:%s\n", i, fd, name);
+	}
+
+	/* Event info */
+	printf("Searching for (max:%d) event file descriptor(s)\n", prog_cnt);
+	for (i = 0; i < prog_cnt; i++) {
+		if (event_fd[i] != -1)
+			printf(" - event_fd[%d] = fd(%d)\n", i, event_fd[i]);
+	}
+}
+
+int main(int argc, char **argv)
+{
+	int longindex = 0, opt;
+	int ret = EXIT_SUCCESS;
+	char bpf_obj_file[256];
+
+	/* Default settings: */
+	bool errors_only = true;
+	int interval = 2;
+
+	snprintf(bpf_obj_file, sizeof(bpf_obj_file), "%s_kern.o", argv[0]);
+
+	/* Parse commands line args */
+	while ((opt = getopt_long(argc, argv, "h",
+				  long_options, &longindex)) != -1) {
+		switch (opt) {
+		case 'D':
+			debug = true;
+			break;
+		case 'S':
+			errors_only = false;
+			break;
+		case 's':
+			interval = atoi(optarg);
+			break;
+		case 'h':
+		default:
+			usage(argv);
+			return EXIT_FAILURE;
+		}
+	}
+
+	if (load_bpf_file(bpf_obj_file)) {
+		printf("ERROR - bpf_log_buf: %s", bpf_log_buf);
+		return 1;
+	}
+	if (!prog_fd[0]) {
+		printf("ERROR - load_bpf_file: %s\n", strerror(errno));
+		return 1;
+	}
+
+	if (debug) {
+		print_bpf_prog_info();
+	}
+
+	/* Unload/stop tracepoint event by closing fd's */
+	if (errors_only) {
+		/* The prog_fd[i] and event_fd[i] depend on the
+		 * order the functions was defined in _kern.c
+		 */
+		close(event_fd[2]); /* tracepoint/xdp/xdp_redirect */
+		close(prog_fd[2]);  /* func: trace_xdp_redirect */
+		close(event_fd[3]); /* tracepoint/xdp/xdp_redirect_map */
+		close(prog_fd[3]);  /* func: trace_xdp_redirect_map */
+	}
+
+	stats_poll(interval, errors_only);
+
+	return ret;
+}

samples/bpf/xdp_redirect_kern.c

@@ -26,6 +26,9 @@ struct bpf_map_def SEC("maps") tx_port = {
 	.max_entries = 1,
 };
 
+/* Count RX packets, as XDP bpf_prog doesn't get direct TX-success
+ * feedback.  Redirect TX errors can be caught via a tracepoint.
+ */
 struct bpf_map_def SEC("maps") rxcnt = {
 	.type = BPF_MAP_TYPE_PERCPU_ARRAY,
 	.key_size = sizeof(u32),
@@ -33,7 +36,6 @@ struct bpf_map_def SEC("maps") rxcnt = {
 	.max_entries = 1,
 };
 
-
 static void swap_src_dst_mac(void *data)
 {
 	unsigned short *p = data;
@@ -78,4 +80,11 @@ int xdp_redirect_prog(struct xdp_md *ctx)
 	return bpf_redirect(*ifindex, 0);
 }
 
+/* Redirect require an XDP bpf_prog loaded on the TX device */
+SEC("xdp_redirect_dummy")
+int xdp_redirect_dummy(struct xdp_md *ctx)
+{
+	return XDP_PASS;
+}
+
 char _license[] SEC("license") = "GPL";

samples/bpf/xdp_redirect_map_kern.c

@@ -26,6 +26,9 @@ struct bpf_map_def SEC("maps") tx_port = {
 	.max_entries = 100,
 };
 
+/* Count RX packets, as XDP bpf_prog doesn't get direct TX-success
+ * feedback.  Redirect TX errors can be caught via a tracepoint.
+ */
 struct bpf_map_def SEC("maps") rxcnt = {
 	.type = BPF_MAP_TYPE_PERCPU_ARRAY,
 	.key_size = sizeof(u32),
@@ -33,7 +36,6 @@ struct bpf_map_def SEC("maps") rxcnt = {
 	.max_entries = 1,
 };
 
-
 static void swap_src_dst_mac(void *data)
 {
 	unsigned short *p = data;
@@ -80,4 +82,11 @@ int xdp_redirect_map_prog(struct xdp_md *ctx)
 	return bpf_redirect_map(&tx_port, vport, 0);
 }
 
+/* Redirect require an XDP bpf_prog loaded on the TX device */
+SEC("xdp_redirect_dummy")
+int xdp_redirect_dummy(struct xdp_md *ctx)
+{
+	return XDP_PASS;
+}
+
 char _license[] SEC("license") = "GPL";

samples/bpf/xdp_redirect_map_user.c

@@ -16,6 +16,7 @@
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdbool.h>
 #include <string.h>
 #include <unistd.h>
 #include <libgen.h>
@@ -26,17 +27,18 @@
 
 static int ifindex_in;
 static int ifindex_out;
+static bool ifindex_out_xdp_dummy_attached = true;
 
 static __u32 xdp_flags;
 
 static void int_exit(int sig)
 {
 	set_link_xdp_fd(ifindex_in, -1, xdp_flags);
+	if (ifindex_out_xdp_dummy_attached)
+		set_link_xdp_fd(ifindex_out, -1, xdp_flags);
 	exit(0);
 }
 
-/* simple per-protocol drop counter
- */
 static void poll_stats(int interval, int ifindex)
 {
 	unsigned int nr_cpus = bpf_num_possible_cpus();
@@ -70,7 +72,6 @@ static void usage(const char *prog)
 		prog);
 }
 
-
 int main(int argc, char **argv)
 {
 	const char *optstr = "SN";
@@ -112,14 +113,21 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	signal(SIGINT, int_exit);
-	signal(SIGTERM, int_exit);
-
 	if (set_link_xdp_fd(ifindex_in, prog_fd[0], xdp_flags) < 0) {
-		printf("link set xdp fd failed\n");
+		printf("ERROR: link set xdp fd failed on %d\n", ifindex_in);
 		return 1;
 	}
 
+	/* Loading dummy XDP prog on out-device */
+	if (set_link_xdp_fd(ifindex_out, prog_fd[1],
+			    (xdp_flags | XDP_FLAGS_UPDATE_IF_NOEXIST)) < 0) {
+		printf("WARN: link set xdp fd failed on %d\n", ifindex_out);
+		ifindex_out_xdp_dummy_attached = false;
+	}
+
+	signal(SIGINT, int_exit);
+	signal(SIGTERM, int_exit);
+
 	printf("map[0] (vports) = %i, map[1] (map) = %i, map[2] (count) = %i\n",
 		map_fd[0], map_fd[1], map_fd[2]);
 

samples/bpf/xdp_redirect_user.c

@@ -16,6 +16,7 @@
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdbool.h>
 #include <string.h>
 #include <unistd.h>
 #include <libgen.h>
@@ -26,17 +27,18 @@
 
 static int ifindex_in;
 static int ifindex_out;
+static bool ifindex_out_xdp_dummy_attached = true;
 
 static __u32 xdp_flags;
 
 static void int_exit(int sig)
 {
 	set_link_xdp_fd(ifindex_in, -1, xdp_flags);
+	if (ifindex_out_xdp_dummy_attached)
+		set_link_xdp_fd(ifindex_out, -1, xdp_flags);
 	exit(0);
 }
 
-/* simple per-protocol drop counter
- */
 static void poll_stats(int interval, int ifindex)
 {
 	unsigned int nr_cpus = bpf_num_possible_cpus();
@@ -112,14 +114,21 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	signal(SIGINT, int_exit);
-	signal(SIGTERM, int_exit);
-
 	if (set_link_xdp_fd(ifindex_in, prog_fd[0], xdp_flags) < 0) {
-		printf("link set xdp fd failed\n");
+		printf("ERROR: link set xdp fd failed on %d\n", ifindex_in);
 		return 1;
 	}
 
+	/* Loading dummy XDP prog on out-device */
+	if (set_link_xdp_fd(ifindex_out, prog_fd[1],
+			    (xdp_flags | XDP_FLAGS_UPDATE_IF_NOEXIST)) < 0) {
+		printf("WARN: link set xdp fd failed on %d\n", ifindex_out);
+		ifindex_out_xdp_dummy_attached = false;
+	}
+
+	signal(SIGINT, int_exit);
+	signal(SIGTERM, int_exit);
+
 	/* bpf redirect port */
 	ret = bpf_map_update_elem(map_fd[0], &key, &ifindex_out, 0);
 	if (ret) {