samples/bpf/bpf_load.c

// SPDX-License-Identifier: GPL-2.0
#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;
	bool is_sockops = strncmp(event, "sockops", 7) == 0;
	bool is_sk_skb = strncmp(event, "sk_skb", 6) == 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 if (is_sockops) {
		prog_type = BPF_PROG_TYPE_SOCK_OPS;
	} else if (is_sk_skb) {
		prog_type = BPF_PROG_TYPE_SK_SKB;
	} 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 || is_sockops || is_sk_skb) {
		if (is_socket)
			event += 6;
		else
			event += 7;
		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;
	err = ioctl(efd, PERF_EVENT_IOC_ENABLE, 0);
	if (err < 0) {
		printf("ioctl PERF_EVENT_IOC_ENABLE failed err %s\n",
		       strerror(errno));
		return -1;
	}
	err = ioctl(efd, PERF_EVENT_IOC_SET_BPF, fd);
	if (err < 0) {
		printf("ioctl PERF_EVENT_IOC_SET_BPF failed err %s\n",
		       strerror(errno));
		return -1;
	}

	return 0;
}

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

	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;
			}
		}

		numa_node = maps[i].def.map_flags & BPF_F_NUMA_NODE ?
			maps[i].def.numa_node : -1;

		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_node(maps[i].def.type,
							maps[i].name,
							maps[i].def.key_size,
							inner_map_fd,
							maps[i].def.max_entries,
							maps[i].def.map_flags,
							numa_node);
		} else {
			map_fd[i] = bpf_create_map_node(maps[i].def.type,
							maps[i].name,
							maps[i].def.key_size,
							maps[i].def.value_size,
							maps[i].def.max_entries,
							maps[i].def.map_flags,
							numa_node);
		}
		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;
	}

	/* process all relo sections, and rewrite bpf insns for 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 (shdr.sh_type == SHT_REL) {
			struct bpf_insn *insns;

			/* locate prog sec that need map fixup (relocations) */
			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[i] = true; /* relo section */

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

	/* load programs */
	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 ||
		    memcmp(shname, "sockops", 7) == 0 ||
		    memcmp(shname, "sk_skb", 6) == 0) {
			ret = load_and_attach(shname, data->d_buf,
					      data->d_size);
			if (ret != 0)
				goto done;
		}
	}

	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;
}