Free Electrons

Embedded Linux Experts

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <libelf.h>
#include <gelf.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <stdbool.h>
#include <stdlib.h>
#include <linux/bpf.h>
#include <linux/filter.h>
#include <linux/perf_event.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <linux/types.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <poll.h>
#include <ctype.h>
#include <assert.h>
#include "libbpf.h"
#include "bpf_load.h"
#include "perf-sys.h"

#define DEBUGFS "/sys/kernel/debug/tracing/"

static char license[128];
static int kern_version;
static bool processed_sec[128];
char bpf_log_buf[BPF_LOG_BUF_SIZE];
int map_fd[MAX_MAPS];
int prog_fd[MAX_PROGS];
int event_fd[MAX_PROGS];
int prog_cnt;
int prog_array_fd = -1;

struct bpf_map_data map_data[MAX_MAPS];
int map_data_count = 0;

static int populate_prog_array(const char *event, int prog_fd)
{
	int ind = atoi(event), err;

	err = bpf_map_update_elem(prog_array_fd, &ind, &prog_fd, BPF_ANY);
	if (err < 0) {
		printf("failed to store prog_fd in prog_array\n");
		return -1;
	}
	return 0;
}

static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
{
	bool is_socket = strncmp(event, "socket", 6) == 0;
	bool is_kprobe = strncmp(event, "kprobe/", 7) == 0;
	bool is_kretprobe = strncmp(event, "kretprobe/", 10) == 0;
	bool is_tracepoint = strncmp(event, "tracepoint/", 11) == 0;
	bool is_xdp = strncmp(event, "xdp", 3) == 0;
	bool is_perf_event = strncmp(event, "perf_event", 10) == 0;
	bool is_cgroup_skb = strncmp(event, "cgroup/skb", 10) == 0;
	bool is_cgroup_sk = strncmp(event, "cgroup/sock", 11) == 0;
	size_t insns_cnt = size / sizeof(struct bpf_insn);
	enum bpf_prog_type prog_type;
	char buf[256];
	int fd, efd, err, id;
	struct perf_event_attr attr = {};

	attr.type = PERF_TYPE_TRACEPOINT;
	attr.sample_type = PERF_SAMPLE_RAW;
	attr.sample_period = 1;
	attr.wakeup_events = 1;

	if (is_socket) {
		prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
	} else if (is_kprobe || is_kretprobe) {
		prog_type = BPF_PROG_TYPE_KPROBE;
	} else if (is_tracepoint) {
		prog_type = BPF_PROG_TYPE_TRACEPOINT;
	} else if (is_xdp) {
		prog_type = BPF_PROG_TYPE_XDP;
	} else if (is_perf_event) {
		prog_type = BPF_PROG_TYPE_PERF_EVENT;
	} else if (is_cgroup_skb) {
		prog_type = BPF_PROG_TYPE_CGROUP_SKB;
	} else if (is_cgroup_sk) {
		prog_type = BPF_PROG_TYPE_CGROUP_SOCK;
	} else {
		printf("Unknown event '%s'\n", event);
		return -1;
	}

	fd = bpf_load_program(prog_type, prog, insns_cnt, license, kern_version,
			      bpf_log_buf, BPF_LOG_BUF_SIZE);
	if (fd < 0) {
		printf("bpf_load_program() err=%d\n%s", errno, bpf_log_buf);
		return -1;
	}

	prog_fd[prog_cnt++] = fd;

	if (is_xdp || is_perf_event || is_cgroup_skb || is_cgroup_sk)
		return 0;

	if (is_socket) {
		event += 6;
		if (*event != '/')
			return 0;
		event++;
		if (!isdigit(*event)) {
			printf("invalid prog number\n");
			return -1;
		}
		return populate_prog_array(event, fd);
	}

	if (is_kprobe || is_kretprobe) {
		if (is_kprobe)
			event += 7;
		else
			event += 10;

		if (*event == 0) {
			printf("event name cannot be empty\n");
			return -1;
		}

		if (isdigit(*event))
			return populate_prog_array(event, fd);

		snprintf(buf, sizeof(buf),
			 "echo '%c:%s %s' >> /sys/kernel/debug/tracing/kprobe_events",
			 is_kprobe ? 'p' : 'r', event, event);
		err = system(buf);
		if (err < 0) {
			printf("failed to create kprobe '%s' error '%s'\n",
			       event, strerror(errno));
			return -1;
		}

		strcpy(buf, DEBUGFS);
		strcat(buf, "events/kprobes/");
		strcat(buf, event);
		strcat(buf, "/id");
	} else if (is_tracepoint) {
		event += 11;

		if (*event == 0) {
			printf("event name cannot be empty\n");
			return -1;
		}
		strcpy(buf, DEBUGFS);
		strcat(buf, "events/");
		strcat(buf, event);
		strcat(buf, "/id");
	}

	efd = open(buf, O_RDONLY, 0);
	if (efd < 0) {
		printf("failed to open event %s\n", event);
		return -1;
	}

	err = read(efd, buf, sizeof(buf));
	if (err < 0 || err >= sizeof(buf)) {
		printf("read from '%s' failed '%s'\n", event, strerror(errno));
		return -1;
	}

	close(efd);

	buf[err] = 0;
	id = atoi(buf);
	attr.config = id;

	efd = sys_perf_event_open(&attr, -1/*pid*/, 0/*cpu*/, -1/*group_fd*/, 0);
	if (efd < 0) {
		printf("event %d fd %d err %s\n", id, efd, strerror(errno));
		return -1;
	}
	event_fd[prog_cnt - 1] = efd;
	ioctl(efd, PERF_EVENT_IOC_ENABLE, 0);
	ioctl(efd, PERF_EVENT_IOC_SET_BPF, fd);

	return 0;
}

static int load_maps(struct bpf_map_data *maps, int nr_maps,
		     fixup_map_cb fixup_map)
{
	int i;

	for (i = 0; i < nr_maps; i++) {
		if (fixup_map) {
			fixup_map(&maps[i], i);
			/* Allow userspace to assign map FD prior to creation */
			if (maps[i].fd != -1) {
				map_fd[i] = maps[i].fd;
				continue;
			}
		}

		if (maps[i].def.type == BPF_MAP_TYPE_ARRAY_OF_MAPS ||
		    maps[i].def.type == BPF_MAP_TYPE_HASH_OF_MAPS) {
			int inner_map_fd = map_fd[maps[i].def.inner_map_idx];

			map_fd[i] = bpf_create_map_in_map(maps[i].def.type,
							maps[i].def.key_size,
							inner_map_fd,
							maps[i].def.max_entries,
							maps[i].def.map_flags);
		} else {
			map_fd[i] = bpf_create_map(maps[i].def.type,
						   maps[i].def.key_size,
						   maps[i].def.value_size,
						   maps[i].def.max_entries,
						   maps[i].def.map_flags);
		}
		if (map_fd[i] < 0) {
			printf("failed to create a map: %d %s\n",
			       errno, strerror(errno));
			return 1;
		}
		maps[i].fd = map_fd[i];

		if (maps[i].def.type == BPF_MAP_TYPE_PROG_ARRAY)
			prog_array_fd = map_fd[i];
	}
	return 0;
}

static int get_sec(Elf *elf, int i, GElf_Ehdr *ehdr, char **shname,
		   GElf_Shdr *shdr, Elf_Data **data)
{
	Elf_Scn *scn;

	scn = elf_getscn(elf, i);
	if (!scn)
		return 1;

	if (gelf_getshdr(scn, shdr) != shdr)
		return 2;

	*shname = elf_strptr(elf, ehdr->e_shstrndx, shdr->sh_name);
	if (!*shname || !shdr->sh_size)
		return 3;

	*data = elf_getdata(scn, 0);
	if (!*data || elf_getdata(scn, *data) != NULL)
		return 4;

	return 0;
}

static int parse_relo_and_apply(Elf_Data *data, Elf_Data *symbols,
				GElf_Shdr *shdr, struct bpf_insn *insn,
				struct bpf_map_data *maps, int nr_maps)
{
	int i, nrels;

	nrels = shdr->sh_size / shdr->sh_entsize;

	for (i = 0; i < nrels; i++) {
		GElf_Sym sym;
		GElf_Rel rel;
		unsigned int insn_idx;
		bool match = false;
		int j, map_idx;

		gelf_getrel(data, i, &rel);

		insn_idx = rel.r_offset / sizeof(struct bpf_insn);

		gelf_getsym(symbols, GELF_R_SYM(rel.r_info), &sym);

		if (insn[insn_idx].code != (BPF_LD | BPF_IMM | BPF_DW)) {
			printf("invalid relo for insn[%d].code 0x%x\n",
			       insn_idx, insn[insn_idx].code);
			return 1;
		}
		insn[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;

		/* Match FD relocation against recorded map_data[] offset */
		for (map_idx = 0; map_idx < nr_maps; map_idx++) {
			if (maps[map_idx].elf_offset == sym.st_value) {
				match = true;
				break;
			}
		}
		if (match) {
			insn[insn_idx].imm = maps[map_idx].fd;
		} else {
			printf("invalid relo for insn[%d] no map_data match\n",
			       insn_idx);
			return 1;
		}
	}

	return 0;
}

static int cmp_symbols(const void *l, const void *r)
{
	const GElf_Sym *lsym = (const GElf_Sym *)l;
	const GElf_Sym *rsym = (const GElf_Sym *)r;

	if (lsym->st_value < rsym->st_value)
		return -1;
	else if (lsym->st_value > rsym->st_value)
		return 1;
	else
		return 0;
}

static int load_elf_maps_section(struct bpf_map_data *maps, int maps_shndx,
				 Elf *elf, Elf_Data *symbols, int strtabidx)
{
	int map_sz_elf, map_sz_copy;
	bool validate_zero = false;
	Elf_Data *data_maps;
	int i, nr_maps;
	GElf_Sym *sym;
	Elf_Scn *scn;
	int copy_sz;

	if (maps_shndx < 0)
		return -EINVAL;
	if (!symbols)
		return -EINVAL;

	/* Get data for maps section via elf index */
	scn = elf_getscn(elf, maps_shndx);
	if (scn)
		data_maps = elf_getdata(scn, NULL);
	if (!scn || !data_maps) {
		printf("Failed to get Elf_Data from maps section %d\n",
		       maps_shndx);
		return -EINVAL;
	}

	/* For each map get corrosponding symbol table entry */
	sym = calloc(MAX_MAPS+1, sizeof(GElf_Sym));
	for (i = 0, nr_maps = 0; i < symbols->d_size / sizeof(GElf_Sym); i++) {
		assert(nr_maps < MAX_MAPS+1);
		if (!gelf_getsym(symbols, i, &sym[nr_maps]))
			continue;
		if (sym[nr_maps].st_shndx != maps_shndx)
			continue;
		/* Only increment iif maps section */
		nr_maps++;
	}

	/* Align to map_fd[] order, via sort on offset in sym.st_value */
	qsort(sym, nr_maps, sizeof(GElf_Sym), cmp_symbols);

	/* Keeping compatible with ELF maps section changes
	 * ------------------------------------------------
	 * The program size of struct bpf_map_def is known by loader
	 * code, but struct stored in ELF file can be different.
	 *
	 * Unfortunately sym[i].st_size is zero.  To calculate the
	 * struct size stored in the ELF file, assume all struct have
	 * the same size, and simply divide with number of map
	 * symbols.
	 */
	map_sz_elf = data_maps->d_size / nr_maps;
	map_sz_copy = sizeof(struct bpf_map_def);
	if (map_sz_elf < map_sz_copy) {
		/*
		 * Backward compat, loading older ELF file with
		 * smaller struct, keeping remaining bytes zero.
		 */
		map_sz_copy = map_sz_elf;
	} else if (map_sz_elf > map_sz_copy) {
		/*
		 * Forward compat, loading newer ELF file with larger
		 * struct with unknown features. Assume zero means
		 * feature not used.  Thus, validate rest of struct
		 * data is zero.
		 */
		validate_zero = true;
	}

	/* Memcpy relevant part of ELF maps data to loader maps */
	for (i = 0; i < nr_maps; i++) {
		unsigned char *addr, *end;
		struct bpf_map_def *def;
		const char *map_name;
		size_t offset;

		map_name = elf_strptr(elf, strtabidx, sym[i].st_name);
		maps[i].name = strdup(map_name);
		if (!maps[i].name) {
			printf("strdup(%s): %s(%d)\n", map_name,
			       strerror(errno), errno);
			free(sym);
			return -errno;
		}

		/* Symbol value is offset into ELF maps section data area */
		offset = sym[i].st_value;
		def = (struct bpf_map_def *)(data_maps->d_buf + offset);
		maps[i].elf_offset = offset;
		memset(&maps[i].def, 0, sizeof(struct bpf_map_def));
		memcpy(&maps[i].def, def, map_sz_copy);

		/* Verify no newer features were requested */
		if (validate_zero) {
			addr = (unsigned char*) def + map_sz_copy;
			end  = (unsigned char*) def + map_sz_elf;
			for (; addr < end; addr++) {
				if (*addr != 0) {
					free(sym);
					return -EFBIG;
				}
			}
		}
	}

	free(sym);
	return nr_maps;
}

static int do_load_bpf_file(const char *path, fixup_map_cb fixup_map)
{
	int fd, i, ret, maps_shndx = -1, strtabidx = -1;
	Elf *elf;
	GElf_Ehdr ehdr;
	GElf_Shdr shdr, shdr_prog;
	Elf_Data *data, *data_prog, *data_maps = NULL, *symbols = NULL;
	char *shname, *shname_prog;
	int nr_maps = 0;

	/* reset global variables */
	kern_version = 0;
	memset(license, 0, sizeof(license));
	memset(processed_sec, 0, sizeof(processed_sec));

	if (elf_version(EV_CURRENT) == EV_NONE)
		return 1;

	fd = open(path, O_RDONLY, 0);
	if (fd < 0)
		return 1;

	elf = elf_begin(fd, ELF_C_READ, NULL);

	if (!elf)
		return 1;

	if (gelf_getehdr(elf, &ehdr) != &ehdr)
		return 1;

	/* clear all kprobes */
	i = system("echo \"\" > /sys/kernel/debug/tracing/kprobe_events");

	/* scan over all elf sections to get license and map info */
	for (i = 1; i < ehdr.e_shnum; i++) {

		if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
			continue;

		if (0) /* helpful for llvm debugging */
			printf("section %d:%s data %p size %zd link %d flags %d\n",
			       i, shname, data->d_buf, data->d_size,
			       shdr.sh_link, (int) shdr.sh_flags);

		if (strcmp(shname, "license") == 0) {
			processed_sec[i] = true;
			memcpy(license, data->d_buf, data->d_size);
		} else if (strcmp(shname, "version") == 0) {
			processed_sec[i] = true;
			if (data->d_size != sizeof(int)) {
				printf("invalid size of version section %zd\n",
				       data->d_size);
				return 1;
			}
			memcpy(&kern_version, data->d_buf, sizeof(int));
		} else if (strcmp(shname, "maps") == 0) {
			int j;

			maps_shndx = i;
			data_maps = data;
			for (j = 0; j < MAX_MAPS; j++)
				map_data[j].fd = -1;
		} else if (shdr.sh_type == SHT_SYMTAB) {
			strtabidx = shdr.sh_link;
			symbols = data;
		}
	}

	ret = 1;

	if (!symbols) {
		printf("missing SHT_SYMTAB section\n");
		goto done;
	}

	if (data_maps) {
		nr_maps = load_elf_maps_section(map_data, maps_shndx,
						elf, symbols, strtabidx);
		if (nr_maps < 0) {
			printf("Error: Failed loading ELF maps (errno:%d):%s\n",
			       nr_maps, strerror(-nr_maps));
			ret = 1;
			goto done;
		}
		if (load_maps(map_data, nr_maps, fixup_map))
			goto done;
		map_data_count = nr_maps;

		processed_sec[maps_shndx] = true;
	}

	/* load programs that need map fixup (relocations) */
	for (i = 1; i < ehdr.e_shnum; i++) {
		if (processed_sec[i])
			continue;

		if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
			continue;
		if (shdr.sh_type == SHT_REL) {
			struct bpf_insn *insns;

			if (get_sec(elf, shdr.sh_info, &ehdr, &shname_prog,
				    &shdr_prog, &data_prog))
				continue;

			if (shdr_prog.sh_type != SHT_PROGBITS ||
			    !(shdr_prog.sh_flags & SHF_EXECINSTR))
				continue;

			insns = (struct bpf_insn *) data_prog->d_buf;

			processed_sec[shdr.sh_info] = true;
			processed_sec[i] = true;

			if (parse_relo_and_apply(data, symbols, &shdr, insns,
						 map_data, nr_maps))
				continue;

			if (memcmp(shname_prog, "kprobe/", 7) == 0 ||
			    memcmp(shname_prog, "kretprobe/", 10) == 0 ||
			    memcmp(shname_prog, "tracepoint/", 11) == 0 ||
			    memcmp(shname_prog, "xdp", 3) == 0 ||
			    memcmp(shname_prog, "perf_event", 10) == 0 ||
			    memcmp(shname_prog, "socket", 6) == 0 ||
			    memcmp(shname_prog, "cgroup/", 7) == 0)
				load_and_attach(shname_prog, insns, data_prog->d_size);
		}
	}

	/* load programs that don't use maps */
	for (i = 1; i < ehdr.e_shnum; i++) {

		if (processed_sec[i])
			continue;

		if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
			continue;

		if (memcmp(shname, "kprobe/", 7) == 0 ||
		    memcmp(shname, "kretprobe/", 10) == 0 ||
		    memcmp(shname, "tracepoint/", 11) == 0 ||
		    memcmp(shname, "xdp", 3) == 0 ||
		    memcmp(shname, "perf_event", 10) == 0 ||
		    memcmp(shname, "socket", 6) == 0 ||
		    memcmp(shname, "cgroup/", 7) == 0)
			load_and_attach(shname, data->d_buf, data->d_size);
	}

	ret = 0;
done:
	close(fd);
	return ret;
}

int load_bpf_file(char *path)
{
	return do_load_bpf_file(path, NULL);
}

int load_bpf_file_fixup_map(const char *path, fixup_map_cb fixup_map)
{
	return do_load_bpf_file(path, fixup_map);
}

void read_trace_pipe(void)
{
	int trace_fd;

	trace_fd = open(DEBUGFS "trace_pipe", O_RDONLY, 0);
	if (trace_fd < 0)
		return;

	while (1) {
		static char buf[4096];
		ssize_t sz;

		sz = read(trace_fd, buf, sizeof(buf));
		if (sz > 0) {
			buf[sz] = 0;
			puts(buf);
		}
	}
}

#define MAX_SYMS 300000
static struct ksym syms[MAX_SYMS];
static int sym_cnt;

static int ksym_cmp(const void *p1, const void *p2)
{
	return ((struct ksym *)p1)->addr - ((struct ksym *)p2)->addr;
}

int load_kallsyms(void)
{
	FILE *f = fopen("/proc/kallsyms", "r");
	char func[256], buf[256];
	char symbol;
	void *addr;
	int i = 0;

	if (!f)
		return -ENOENT;

	while (!feof(f)) {
		if (!fgets(buf, sizeof(buf), f))
			break;
		if (sscanf(buf, "%p %c %s", &addr, &symbol, func) != 3)
			break;
		if (!addr)
			continue;
		syms[i].addr = (long) addr;
		syms[i].name = strdup(func);
		i++;
	}
	sym_cnt = i;
	qsort(syms, sym_cnt, sizeof(struct ksym), ksym_cmp);
	return 0;
}

struct ksym *ksym_search(long key)
{
	int start = 0, end = sym_cnt;
	int result;

	while (start < end) {
		size_t mid = start + (end - start) / 2;

		result = key - syms[mid].addr;
		if (result < 0)
			end = mid;
		else if (result > 0)
			start = mid + 1;
		else
			return &syms[mid];
	}

	if (start >= 1 && syms[start - 1].addr < key &&
	    key < syms[start].addr)
		/* valid ksym */
		return &syms[start - 1];

	/* out of range. return _stext */
	return &syms[0];
}

int set_link_xdp_fd(int ifindex, int fd, __u32 flags)
{
	struct sockaddr_nl sa;
	int sock, seq = 0, len, ret = -1;
	char buf[4096];
	struct nlattr *nla, *nla_xdp;
	struct {
		struct nlmsghdr  nh;
		struct ifinfomsg ifinfo;
		char             attrbuf[64];
	} req;
	struct nlmsghdr *nh;
	struct nlmsgerr *err;

	memset(&sa, 0, sizeof(sa));
	sa.nl_family = AF_NETLINK;

	sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
	if (sock < 0) {
		printf("open netlink socket: %s\n", strerror(errno));
		return -1;
	}

	if (bind(sock, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
		printf("bind to netlink: %s\n", strerror(errno));
		goto cleanup;
	}

	memset(&req, 0, sizeof(req));
	req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg));
	req.nh.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
	req.nh.nlmsg_type = RTM_SETLINK;
	req.nh.nlmsg_pid = 0;
	req.nh.nlmsg_seq = ++seq;
	req.ifinfo.ifi_family = AF_UNSPEC;
	req.ifinfo.ifi_index = ifindex;

	/* started nested attribute for XDP */
	nla = (struct nlattr *)(((char *)&req)
				+ NLMSG_ALIGN(req.nh.nlmsg_len));
	nla->nla_type = NLA_F_NESTED | 43/*IFLA_XDP*/;
	nla->nla_len = NLA_HDRLEN;

	/* add XDP fd */
	nla_xdp = (struct nlattr *)((char *)nla + nla->nla_len);
	nla_xdp->nla_type = 1/*IFLA_XDP_FD*/;
	nla_xdp->nla_len = NLA_HDRLEN + sizeof(int);
	memcpy((char *)nla_xdp + NLA_HDRLEN, &fd, sizeof(fd));
	nla->nla_len += nla_xdp->nla_len;

	/* if user passed in any flags, add those too */
	if (flags) {
		nla_xdp = (struct nlattr *)((char *)nla + nla->nla_len);
		nla_xdp->nla_type = 3/*IFLA_XDP_FLAGS*/;
		nla_xdp->nla_len = NLA_HDRLEN + sizeof(flags);
		memcpy((char *)nla_xdp + NLA_HDRLEN, &flags, sizeof(flags));
		nla->nla_len += nla_xdp->nla_len;
	}

	req.nh.nlmsg_len += NLA_ALIGN(nla->nla_len);

	if (send(sock, &req, req.nh.nlmsg_len, 0) < 0) {
		printf("send to netlink: %s\n", strerror(errno));
		goto cleanup;
	}

	len = recv(sock, buf, sizeof(buf), 0);
	if (len < 0) {
		printf("recv from netlink: %s\n", strerror(errno));
		goto cleanup;
	}

	for (nh = (struct nlmsghdr *)buf; NLMSG_OK(nh, len);
	     nh = NLMSG_NEXT(nh, len)) {
		if (nh->nlmsg_pid != getpid()) {
			printf("Wrong pid %d, expected %d\n",
			       nh->nlmsg_pid, getpid());
			goto cleanup;
		}
		if (nh->nlmsg_seq != seq) {
			printf("Wrong seq %d, expected %d\n",
			       nh->nlmsg_seq, seq);
			goto cleanup;
		}
		switch (nh->nlmsg_type) {
		case NLMSG_ERROR:
			err = (struct nlmsgerr *)NLMSG_DATA(nh);
			if (!err->error)
				continue;
			printf("nlmsg error %s\n", strerror(-err->error));
			goto cleanup;
		case NLMSG_DONE:
			break;
		}
	}

	ret = 0;

cleanup:
	close(sock);
	return ret;
}