#define _GNU_SOURCE
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sched.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

void slurp(const char *fn)
{
	char buf[8192];
	ssize_t r;
	int fd;

	printf("%s [pid: %d]\n", fn, getpid()); fflush(stdout);

	fd = open(fn, O_RDONLY);
	if (fd < 0) { perror("open"); exit(1); }

	r = read(fd, buf, sizeof(buf)-1);
	if (r < 0) { perror("read"); exit(1); }
	buf[r] = 0;
	puts(buf); fflush(stdout);

	if (close(fd) < 0) { perror("close"); exit(1); }
}

void newnet(const char *ns)
{
	int fd;
	fd = open(ns, O_RDONLY);
	if (fd < 0) { perror("open"); exit(1); }
	if (setns(fd, CLONE_NEWNET) < 0) { perror("setns"); exit(1); }
	if (close(fd) < 0) { perror("close"); exit(1); }
}

int main(int argc, char **argv)
{
	const char *ns = "/run/netns/test";
	const char *fn = "/proc/net/sctp/snmp";
	int d = 1;

	// Optional args: /run/netns/... /proc/net/... n
	if (argc >= 2) ns = argv[1];
	if (argc >= 3) fn = argv[2];
	if (argc >= 4 && argv[3][0] == 'n') d = 0;

	if (d) slurp(fn);
	printf("setns(%s) ...\n", ns); fflush(stdout);
	newnet(ns);
	slurp(fn);
}