88 lines
2.2 KiB
C++
88 lines
2.2 KiB
C++
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#include <sys/socket.h>
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#include <fcntl.h>
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#include <linux/if.h>
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#include <linux/if_tun.h>
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#include <string.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/ioctl.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <unistd.h>
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int tun_alloc(char *dev, int flags) {
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struct ifreq ifr;
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int fd, err;
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const char *clonedev = "/dev/net/tun";
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/* Arguments taken by the function:
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*
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* char *dev: the name of an interface (or '\0'). MUST have enough
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* space to hold the interface name if '\0' is passed
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* int flags: interface flags (eg, IFF_TUN etc.)
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*/
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/* open the clone device */
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if( (fd = open(clonedev, O_RDWR)) < 0 ) {
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return fd;
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}
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/* preparation of the struct ifr, of type "struct ifreq" */
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memset(&ifr, 0, sizeof(ifr));
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ifr.ifr_flags = flags; /* IFF_TUN or IFF_TAP, plus maybe IFF_NO_PI */
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if (*dev) {
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/* if a device name was specified, put it in the structure; otherwise,
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* the kernel will try to allocate the "next" device of the
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* specified type */
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strncpy(ifr.ifr_name, dev, IFNAMSIZ);
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}
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/* try to create the device */
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if( (err = ioctl(fd, TUNSETIFF, (void *) &ifr)) < 0 ) {
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close(fd);
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return err;
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}
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/* if the operation was successful, write back the name of the
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* interface to the variable "dev", so the caller can know
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* it. Note that the caller MUST reserve space in *dev (see calling
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* code below) */
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strcpy(dev, ifr.ifr_name);
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/* this is the special file descriptor that the caller will use to talk
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* with the virtual interface */
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return fd;
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}
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int main(int argc, char *argv[]) {
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char tun_name[IFNAMSIZ];
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/* Connect to the device */
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strcpy(tun_name, "tun77");
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int tun_fd = tun_alloc(tun_name, IFF_TUN); /* tun interface */
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if(tun_fd < 0){
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perror("Allocating interface");
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exit(1);
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}
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char buffer[2048];
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/* Now read data coming from the kernel */
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while(1) {
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/* Note that "buffer" should be at least the MTU size of the interface, eg 1500 bytes */
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int nread = read(tun_fd,buffer,sizeof(buffer));
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if(nread < 0) {
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perror("Reading from interface");
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close(tun_fd);
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exit(1);
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}
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/* Do whatever with the data */
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printf("Read %d bytes from device %s\n", nread, tun_name);
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}
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return 0;
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}
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