examples/bpf/bpf_agent.c

/*
 * eBPF user space agent part
 *
 * Simple, _self-contained_ user space agent for the eBPF kernel
 * ebpf_prog.c program, which gets all map fds passed from tc via unix
 * domain socket in one transaction and can thus keep referencing
 * them from user space in order to read out (or possibly modify)
 * map data. Here, just as a minimal example to display counters.
 *
 * The agent only uses the bpf(2) syscall API to read or possibly
 * write to eBPF maps, it doesn't need to be aware of the low-level
 * bytecode parts and/or ELF parsing bits.
 *
 * ! For more details, see header comment in bpf_prog.c !
 *
 * gcc bpf_agent.c -o bpf_agent -Wall -O2
 *
 * For example, a more complex user space agent could run on each
 * host, reading and writing into eBPF maps used by tc classifier
 * and actions. It would thus allow for implementing a distributed
 * tc architecture, for example, which would push down central
 * policies into eBPF maps, and thus altering run-time behaviour.
 *
 *   -- Happy eBPF hacking! ;)
 */

#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <stdint.h>
#include <assert.h>

#include <sys/un.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>

/* Just some misc macros as min(), offsetof(), etc. */
#include "../../include/utils.h"
/* Common code from fd passing. */
#include "../../include/bpf_scm.h"
/* Common, shared definitions with ebpf_prog.c */
#include "bpf_shared.h"
/* Mini syscall wrapper */
#include "bpf_sys.h"

static void bpf_dump_drops(int fd)
{
	int cpu, max;

	max = sysconf(_SC_NPROCESSORS_ONLN);

	printf(" `- number of drops:");
	for (cpu = 0; cpu < max; cpu++) {
		long drops;

		assert(bpf_lookup_elem(fd, &cpu, &drops) == 0);
		printf("\tcpu%d: %5ld", cpu, drops);
	}
	printf("\n");
}

static void bpf_dump_queue(int fd)
{
	/* Just for the same of the example. */
	int max_queue = 4, i;

	printf("  | nic queues:");
	for (i = 0; i < max_queue; i++) {
		struct count_queue cq;
		int ret;

		memset(&cq, 0, sizeof(cq));
		ret = bpf_lookup_elem(fd, &i, &cq);
		assert(ret == 0 || (ret < 0 && errno == ENOENT));

		printf("\tq%d:[pkts: %ld, mis: %ld]",
		       i, cq.total, cq.mismatch);
	}
	printf("\n");
}

static void bpf_dump_proto(int fd)
{
	uint8_t protos[] = { IPPROTO_TCP, IPPROTO_UDP, IPPROTO_ICMP };
	char *names[] = { "tcp", "udp", "icmp" };
	int i;

	printf("  ` protos:");
	for (i = 0; i < ARRAY_SIZE(protos); i++) {
		struct count_tuple ct;
		int ret;

		memset(&ct, 0, sizeof(ct));
		ret = bpf_lookup_elem(fd, &protos[i], &ct);
		assert(ret == 0 || (ret < 0 && errno == ENOENT));

		printf("\t%s:[pkts: %ld, bytes: %ld]",
		       names[i], ct.packets, ct.bytes);
	}
	printf("\n");
}

static void bpf_dump_map_data(int *tfd)
{
	int i;

	for (i = 0; i < 30; i++) {
		const int period = 5;

		printf("data, period: %dsec\n", period);

		bpf_dump_drops(tfd[BPF_MAP_ID_DROPS]);
		bpf_dump_queue(tfd[BPF_MAP_ID_QUEUE]);
		bpf_dump_proto(tfd[BPF_MAP_ID_PROTO]);

		sleep(period);
	}
}

static void bpf_info_loop(int *fds, struct bpf_map_aux *aux)
{
	int i, tfd[BPF_MAP_ID_MAX];

	printf("ver: %d\nobj: %s\ndev: %lu\nino: %lu\nmaps: %u\n",
	       aux->uds_ver, aux->obj_name, aux->obj_st.st_dev,
	       aux->obj_st.st_ino, aux->num_ent);

	for (i = 0; i < aux->num_ent; i++) {
		printf("map%d:\n", i);
		printf(" `- fd: %u\n", fds[i]);
		printf("  | serial: %u\n", aux->ent[i].id);
		printf("  | type: %u\n", aux->ent[i].type);
		printf("  | max elem: %u\n", aux->ent[i].max_elem);
		printf("  | size key: %u\n", aux->ent[i].size_key);
		printf("  ` size val: %u\n", aux->ent[i].size_value);

		tfd[aux->ent[i].id] = fds[i];
	}

	bpf_dump_map_data(tfd);
}

static void bpf_map_get_from_env(int *tfd)
{
	char key[64], *val;
	int i;

	for (i = 0; i < BPF_MAP_ID_MAX; i++) {
		memset(key, 0, sizeof(key));
		snprintf(key, sizeof(key), "BPF_MAP%d", i);

		val = getenv(key);
		assert(val != NULL);

		tfd[i] = atoi(val);
	}
}

static int bpf_map_set_recv(int fd, int *fds,  struct bpf_map_aux *aux,
			    unsigned int entries)
{
	struct bpf_map_set_msg msg;
	int *cmsg_buf, min_fd, i;
	char *amsg_buf, *mmsg_buf;

	cmsg_buf = bpf_map_set_init(&msg, NULL, 0);
	amsg_buf = (char *)msg.aux.ent;
	mmsg_buf = (char *)&msg.aux;

	for (i = 0; i < entries; i += min_fd) {
		struct cmsghdr *cmsg;
		int ret;

		min_fd = min(BPF_SCM_MAX_FDS * 1U, entries - i);

		bpf_map_set_init_single(&msg, min_fd);

		ret = recvmsg(fd, &msg.hdr, 0);
		if (ret <= 0)
			return ret ? : -1;

		cmsg = CMSG_FIRSTHDR(&msg.hdr);
		if (!cmsg || cmsg->cmsg_type != SCM_RIGHTS)
			return -EINVAL;
		if (msg.hdr.msg_flags & MSG_CTRUNC)
			return -EIO;

		min_fd = (cmsg->cmsg_len - sizeof(*cmsg)) / sizeof(fd);
		if (min_fd > entries || min_fd <= 0)
			return -1;

		memcpy(&fds[i], cmsg_buf, sizeof(fds[0]) * min_fd);
		memcpy(&aux->ent[i], amsg_buf, sizeof(aux->ent[0]) * min_fd);
		memcpy(aux, mmsg_buf, offsetof(struct bpf_map_aux, ent));

		if (i + min_fd == aux->num_ent)
			break;
	}

	return 0;
}

int main(int argc, char **argv)
{
	int fds[BPF_SCM_MAX_FDS];
	struct bpf_map_aux aux;
	struct sockaddr_un addr;
	int fd, ret, i;

	/* When arguments are being passed, we take it as a path
	 * to a Unix domain socket, otherwise we grab the fds
	 * from the environment to demonstrate both possibilities.
	 */
	if (argc == 1) {
		int tfd[BPF_MAP_ID_MAX];

		bpf_map_get_from_env(tfd);
		bpf_dump_map_data(tfd);

		return 0;
	}

	fd = socket(AF_UNIX, SOCK_DGRAM, 0);
	if (fd < 0) {
		fprintf(stderr, "Cannot open socket: %s\n",
			strerror(errno));
		exit(1);
	}

	memset(&addr, 0, sizeof(addr));
	addr.sun_family = AF_UNIX;
	strncpy(addr.sun_path, argv[argc - 1], sizeof(addr.sun_path));

	ret = bind(fd, (struct sockaddr *)&addr, sizeof(addr));
	if (ret < 0) {
		fprintf(stderr, "Cannot bind to socket: %s\n",
			strerror(errno));
		exit(1);
	}

	memset(fds, 0, sizeof(fds));
	memset(&aux, 0, sizeof(aux));

	ret = bpf_map_set_recv(fd, fds, &aux, BPF_SCM_MAX_FDS);
	if (ret >= 0)
		bpf_info_loop(fds, &aux);

	for (i = 0; i < aux.num_ent; i++)
		close(fds[i]);

	close(fd);
	return 0;
}