tun-tap 0.1.4

TUN/TAP interface wrapper
Documentation 
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/*
 * Since the rust ioctl bindings don't have all the structures and constants,
 * it's easier to just write the thing in C and link it in.
 */

#include <assert.h>
#include <stdint.h>
#include <string.h>

#include <sys/socket.h>
#ifdef __linux__
#include <linux/if.h>
#include <linux/if_tun.h>
#else
#include <net/if.h>
#define IFF_TUN 0x0001
#define IFF_TAP 0x0002
#define IFF_NO_PI 0x1000
#define TUNSETIFF _IOW('T', 202, int)
#endif
#include <sys/ioctl.h>

/**
 * fd ‒ the fd to turn into TUN or TAP.
 * name ‒ the name to use. If empty, kernel will assign something by itself.
 *   Must be buffer with capacity at least 33.
 * mode ‒ 1 = TUN, 2 = TAP.
 * packet_info ‒ if packet info should be provided, if the given value is 0 it will not prepend packet info.
 */
int tuntap_setup(int fd, unsigned char *name, int mode, int packet_info) {
	struct ifreq ifr;
	memset(&ifr, 0, sizeof ifr);
	switch (mode) {
		case 1:
			ifr.ifr_flags = IFF_TUN;
			break;
		case 2:
			ifr.ifr_flags = IFF_TAP;
			break;
		default:
			assert(0);
	}

	// If no packet info needs to be provided add corresponding flag
	if (!packet_info) {
		ifr.ifr_flags |= IFF_NO_PI;
	}

	// Leave one for terminating '\0'. No idea if it is needed, didn't find
	// it in the docs, but assuming the worst.
	strncpy(ifr.ifr_name, (char *)name, IFNAMSIZ - 1);

	int ioresult = ioctl(fd, TUNSETIFF, &ifr);
	if (ioresult < 0) {
		return ioresult;
	}
	strncpy((char *)name, ifr.ifr_name, IFNAMSIZ < 32 ? IFNAMSIZ : 32);
	name[32] = '\0';
	return 0;
}