Using Ubuntu 16.04, kernel 4.17.4
I am trying the following code where I have defined a shared memory and mapped current process's address space to the shared memory. When I use MAP_FIXED in mmap() it shows:
mmap: Invalid argument
The code is as follows:
#include <stdio.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#define STORAGE_ID "/SHM_TEST"
#define STORAGE_SIZE 4096
int main(int argc, char *argv[])
{
int res, temp;
int fd;
int len;
pid_t pid;
void *addr;
char data[STORAGE_SIZE];
fd = shm_open(STORAGE_ID, O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
if (fd == -1)
{
perror("open");
return 10;
}
res = ftruncate(fd, STORAGE_SIZE);
if (res == -1)
{
perror("ftruncate");
return 20;
}
addr = mmap(NULL, STORAGE_SIZE, PROT_WRITE, MAP_FIXED, fd, 0);
if (addr == MAP_FAILED)
{
perror("mmap");
return 30;
}
res = munmap(addr, STORAGE_SIZE);
if (res == -1)
{
perror("munmap");
return 40;
}
// shm_open cleanup
fd = shm_unlink(STORAGE_ID);
if (fd == -1)
{
perror("unlink");
return 100;
}
return 0;
}
The reason I am using MAP_FIXED is I will manually put an address instead of NULL (tried this and got same error). What do I need to do to use MAP_FIXED with mmap()?
Related
I'm trying to use named pipe in Linux, using mkfifo.
Below are codes for sender / reader of named pipe :
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#define MSG_SIZE 100
//SENDER
int main() {
char msg[MSG_SIZE] = "FIFO is for first-in, first-out.";
int fd;
int cnt;
if(fd = open("./hello", O_RDWR) < 0) { //fifo acts as a typical file
perror("Failed to make fifo : ");
printf("Error : %d\n", errno);
exit(1);
}
int len = strlen(msg) + 1;
while(1) {
if(write(fd, msg, len) == -1) {
perror("Failed to write into fifo : ");
exit(1);
}
else{
printf("Succeed to write msg!");
break;
}
}
sleep(1);
return 0;
}
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#define MSG_SIZE 100
//READER
int main() {
char msg_rc[MSG_SIZE];
int fd;
if(access("./hello",F_OK) == 0) {
fd = open("./hello", O_RDWR);
if(fd < 0) {
perror("Failed to open fifo : ");
exit(1);
}
}
else {
if(fd = mkfifo("./hello", O_RDWR) < 0) {
perror("Failed to open fifo : ");
exit(1);
}
}
printf("Waiting for fifo update");
while(1) {
if(read(fd, msg_rc, MSG_SIZE) == -1) {
perror("Failed to read from fifo : ");
exit(1);
}
printf("Read msg : %s\n", msg_rc);
break;
}
return 0;
}
When I used these codes,
% ./fifoSender
FIFO is for first-in, first-out.Succeed to write msg!%
% ./fifoReader
fifoSender shows msg, and fifoReader shows no msg, which are not desirable behavior.
Any advice will be helpful. Thanks in advance
The main problem is these two lines
if(fd = open("./hello", O_RDWR) < 0) {
if(fd = mkfifo("./hello", O_RDWR) < 0) {
They don't do what you think they do.
Firstly, O_RDWR is a wrong argument for mkfifo. It expects Unix file permissions mask, such as S_IRWU"S_IRWG|S_IRWO, or just 0666.
Secondly and most importantly, since the priority of = is lower than that of <, they are parsed like this:
if(fd = (open("./hello", O_RDWR) < 0)) {
Now, when open("./hello", O_RDWR) is less than 0 (which is highly likely, given that it is either never created or created with an incorrect mode), fd becomes 1, which is the standard output file descriptor.
The correct incantation is
if((fd = open("./hello", O_RDWR)) < 0) { // note () around assignment
if((fd = mkfifo("./hello", 0666)) < 0) {
There are several more subtle shortcomings.
Here is the working code,
// sender
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#define PIPE_NAME "./hello"
int main(int argc, char *argv[])
{
const char *message = "FIFO is for first-in, first-out\n";
// Open the pipe for writing
int pipe_fd = open(PIPE_NAME, O_WRONLY);
if (pipe_fd < 0) {
perror("open");
exit(1);
}
// Write data to the pipe
while(1){
int n = write(pipe_fd, message, strlen(message));
if (n < 0) {
perror("write");
exit(1);
}
sleep(1);
}
// Close the pipe
close(pipe_fd);
return 0;
}
//receiver
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#define PIPE_NAME "./hello"
int main(int argc, char *argv[])
{
// Create the named pipe
mknod(PIPE_NAME, S_IFIFO | 0666, 0);
// Open the pipe for reading
int pipe_fd = open(PIPE_NAME, O_RDONLY);
if (pipe_fd < 0) {
perror("open");
exit(1);
}
// Read data from the pipe
char buffer[1024];
while(1){
int n = read(pipe_fd, buffer, sizeof(buffer));
if (n < 0) {
perror("read");
exit(1);
}
// Print the data that was read
printf("Received: %.*s\n", n, buffer);
}
// Close the pipe
close(pipe_fd);
return 0;
}
As title, but the measurement result is unreasonable. Let me describe the current status.
I'm using syscall getuid as measurement target, I started by measureing the complete overhead with two clock_gettime bounded around, then measure the entry (what SYSCALL instruction does before executing the actual getuid code) and leaving overhead saparately (with eBPF program hook onto the entry and leaving point).
The result for the complete overhead is ~65ns, and regarding to the entry and leaving overhead, it's ~77ns and ~70ns respectively.
It's obvious that my measurement has some additional overhead except the typical overhead. However, it's weird that since clock_gettime is a vDSO syscall, it should barely have noticeable overhead. And BPF, which is a lightweight instrumental tool (JIT-ed and etc.) these day in Linux, shouldn't have noticeable overhead too.
Is there anyone have idea what additional overhead my measurement incurs?
Following is my measurement code:
userland (measuring the return-from-kernel overhead):
#define _GNU_SOURCE
#include <bpf.h>
#include <libbpf.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <string.h>
#include <asm/errno.h>
#include <linux/if_link.h>
#include <errno.h>
#include <sys/resource.h>
#include <unistd.h>
#include <asm/unistd.h>
#include <time.h>
#include <linux/perf_event.h>
#include <linux/hw_breakpoint.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <sched.h>
#define likely(x) __builtin_expect((x),1)
#define unlikely(x) __builtin_expect((x),0)
#define TEST_CNT 1000000
#define BPF_FILE_NAME "mkern.o"
#define BPF_MAP_NAME "msys"
static inline int sys_perf_event_open(struct perf_event_attr *attr, pid_t pid,
int cpu, int group_fd,
unsigned long flags)
{
attr->size = sizeof(*attr);
return syscall(__NR_perf_event_open, attr, pid, cpu, group_fd, flags);
}
static int attach_kprobe(int prog_fd)
{
int err, fd, id;
char buf[32];
struct perf_event_attr attr = {};
err = system("echo 'r:kp_sys_batch __x64_sys_getuid' > /sys/kernel/debug/tracing/kprobe_events");
if (err < 0) {
fprintf(stderr, "Failed to create kprobe, error '%s'\n", strerror(errno));
return -1;
}
fd = open("/sys/kernel/debug/tracing/events/kprobes/kp_sys_batch/id", O_RDONLY, 0);
if (fd < 0) {
fprintf(stderr, "Failed to open event %s\n", "sys_batch");
return -1;
}
err = read(fd, buf, sizeof(buf));
if (err < 0 || err >= sizeof(buf)) {
fprintf(stderr, "read from '%s' failed '%s'\n", "sys_batch", strerror(errno));
return -1;
}
close(fd);
buf[err] = 0;
id = atoi(buf);
attr.config = id;
attr.type = PERF_TYPE_TRACEPOINT;
attr.sample_type = PERF_SAMPLE_RAW;
attr.sample_period = 1;
attr.wakeup_events = 1;
fd = sys_perf_event_open(&attr, 0/*this process*/, -1/*any cpu*/, -1/*group leader*/, 0);
if (fd < 0) {
perror("sys_perf_event_open");
fprintf(stderr, "Failed to open perf_event (id: %llu)\n", attr.config);
return -1;
}
err = ioctl(fd, PERF_EVENT_IOC_ENABLE, 0);
if (err < 0) {
fprintf(stderr, "ioctl PERF_EVENT_IOC_ENABLE failed err %s\n",
strerror(errno));
return -1;
}
err = ioctl(fd, PERF_EVENT_IOC_SET_BPF, prog_fd);
if (err < 0) {
fprintf(stderr, "ioctl PERF_EVENT_IOC_SET_BPF failed: %s\n",
strerror(errno));
return -1;
}
return 0;
}
static void maxi_memlock_rlimit(void)
{
struct rlimit rlim_new = {
.rlim_cur = RLIM_INFINITY,
.rlim_max = RLIM_INFINITY,
};
if (setrlimit(RLIMIT_MEMLOCK, &rlim_new)) {
fprintf(stderr, "Failed to increase RLIMIT_MEMLOCK limit!\n");
exit(-1);
}
}
static int find_map_fd(struct bpf_object *bpf_obj, const char *mapname)
{
struct bpf_map *map;
int map_fd = -1;
map = bpf_object__find_map_by_name(bpf_obj, mapname);
if (!map) {
fprintf(stderr, "Failed finding map by name: %s\n", mapname);
exit(-1);
}
map_fd = bpf_map__fd(map);
return map_fd;
}
int main(int argc, char **argv)
{
int bpf_map_fd;
int bpf_prog_fd = -1;
int err;
int key = 0;
struct timespec tp;
struct bpf_object *bpf_obj;
struct reals map;
struct bpf_prog_load_attr xattr = {
.prog_type = BPF_PROG_TYPE_KPROBE,
.file = BPF_FILE_NAME,
};
maxi_memlock_rlimit();
err = bpf_prog_load_xattr(&xattr, &bpf_obj, &bpf_prog_fd);
if (err) {
fprintf(stderr, "Failed loading bpf object file\n");
exit(-1);
}
if (attach_kprobe(bpf_prog_fd)) {
fprintf(stderr, "Failed attaching kprobe\n");
exit(-1);
}
bpf_map_fd = find_map_fd(bpf_obj, BPF_MAP_NAME);
if (find_map_fd < 0) {
fprintf(stderr, "Failed finding map fd\n");
exit(-1);
}
/* warm up */
for (int i = 0; i < TEST_CNT; i++) {
syscall(__NR_getuid); /* dummy call */
clock_gettime(CLOCK_MONOTONIC, &tp);
if (unlikely(bpf_map_lookup_elem(bpf_map_fd, &key, &map))) {
fprintf(stderr, "Failed to lookup map element\n");
perror("lookup");
exit(-1);
}
}
uint64_t delta = 0;
for (int i = 0; i < TEST_CNT; i++) {
syscall(__NR_getuid); /* dummy call */
clock_gettime(CLOCK_MONOTONIC, &tp);
if (unlikely(bpf_map_lookup_elem(bpf_map_fd, &key, &map))) {
fprintf(stderr, "Failed to lookup map element\n");
perror("lookup");
exit(-1);
}
delta += (1000000000 * tp.tv_sec + tp.tv_nsec) - map.ts;
}
printf("avg: %fns\n", (double) delta / TEST_CNT);
return 0;
}
user land (measuring the enter-kernel overhead, almost same as the above, except what I pointed out):
err = system("echo 'p:kp_sys_batch sys_batch' > /sys/kernel/debug/tracing/kprobe_events");
...
clock_gettime(CLOCK_MONOTONIC, &tp);
syscall(__NR_getuid); /* dummy call */
...
delta += map.ts - (1000000000 * tp.tv_sec + tp.tv_nsec);
kernel land:
SEC("getuid")
int kp_sys_batch(struct pt_regs *ctx)
{
__u32 i = 0;
struct reals *r;
r = bpf_map_lookup_elem(&reals, &i);
if (!r)
return 1;
r->ts = bpf_ktime_get_ns();
return 0;
}
Except the additional overhead I mentioned above, inside the return-from-kernel measurement code, if the echo 'r:kp_sys_batch sys_batch' is changed to echo 'p:kp_sys_batch sys_batch' (which means that the measurement would take the syscall execution overhead into account), the result would be ~48ns, this means that the result includes overhead of syscall execution and return-from-kernel. Any idea why this could be only ~48ns?
Thanks!
I am trying to understand procfs for communication between userspace and kernel module. My module has basic two functions for procfs write_proc, driver_mmap.
I call multiple times write_proc by calling fputs("123456789",fd). where fd is file descriptor to procfs entry in /proc directory. But I don't see write_proc called multiple time. Code is attached by here.
<code>
#include <linux/init.h>
#include <linux/pci.h>
#include <linux/slab.h>
#include <sound/core.h>
#include <sound/initval.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/proc_fs.h>
#include <asm/uaccess.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/mm.h> /* mmap related stuff */
#define BUF_SIZE 64 * 1024
int *MmapBuffer;
int Factor = 1;
static int write_proc(struct file *filp, int *buf, size_t count, loff_t *offp)
{
int rc,i;
printk("in Write \n");
for (i = 1; i <= 16*1024 ; i++)
MmapBuffer[i-1] = (i+1)*Factor;
Factor++;
return count;
}
static int driver_mmap(struct file *file, struct vm_area_struct *vma)
{
int ret;
vma->vm_flags |= VM_LOCKED|VM_SHARED;
ret = remap_pfn_range(vma, vma->vm_start,
virt_to_phys(MmapBuffer) >> PAGE_SHIFT,
vma->vm_end-vma->vm_start, vma->vm_page_prot);
if(ret != 0)
printk("MMAP Failed \n");
SetPageReserved(virt_to_page(MmapBuffer));
printk("MMAP Succeeded \n");
return 0;
}
// file operations
struct file_operations proc_fops =
{
.write = write_proc,
.mmap = driver_mmap,
};
// init module
int init_module_test(void)
{
printk("<1>Hello world\n");
MmapBuffer = kzalloc(BUF_SIZE,__GFP_COLD|GFP_DMA);
if(MmapBuffer == NULL)
printk("Kzalloc failed. reduce buffer size \n");
proc_create ("Test_fs",0,NULL, &proc_fops);
return 0;
}
// exit module
void cleanup_module_test(void)
{
kfree(MmapBuffer);
remove_proc_entry ("Test_fs", NULL);
printk("Goodbye world\n");
}
module_init(init_module_test);
module_exit(cleanup_module_test);
MODULE_LICENSE("GPL");
</code>
Application code
<code>
#include<stdio.h>
#include<stdlib.h>
#include<sys/mman.h>
#include<errno.h>
#include <fcntl.h>
int main(void)
{
int fd;
int i,j;
int *msg ;
printf("Allocation started \n ");
msg=(int*)malloc(64*1024);
if(msg == NULL)
printf("Allocation failed \n");
//unsigned int *addr;
printf("Starting opening \n ");
if((fd=open("/proc/Test_fs", O_RDONLY ))<0)
{
printf("File not opened ");
}
printf("Starting mapping \n ");
msg = mmap(NULL, 64*1024, PROT_READ, MAP_SHARED , fd, 0);
printf("done from module \n ");
if(msg == MAP_FAILED)
{
printf("MAP failed and error is %s", strerror(errno));
return 0;
}
close(fd);
printf("Successful mapping");
FILE *f;
f=fopen("/proc/Test_fs", "wr");
if(!f)
{
printf("File not opened ");
}
for (j = 0; j < 10 ; j++)
{
if(fputs("1234567890,",f) <= 0)
printf("write failed, ");
for (i = 0; i < 16*1024 ; i++)
printf("%d, ", msg[i]);
printf("\n \n done \n \n ");
}
fclose(f);
return 0;
}
</code>
Hi am trying to implement net link user code and kernel code every thing works fine for unicast (src_addr.nl_groups = 0;). For mulicast, user code bind call always fails for non zero src_addr.nl_groups value. Really am not sure what value to put for multicast and how to proceed further. I checked the usage of netlink_broadcast in kernel source tree, so I put the same group Id value (RTMGRP_LINK) here. For unicast I found good number of help in internet but for multicast I don't think so . So Please help me to proceed further.
Error am getting is:
bind: No such file or directory
./a.out: can't bind socket (3)and err : -1: No such file or directory
#include <sys/socket.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <stdio.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#define NETLINK_TEST 28
#define GROUP_IB 1
#define MAX_PAYLOAD 1024
struct sockaddr_nl src_addr, dst_addr;
struct nlmsghdr *nlh = NULL;
struct msghdr msg;
struct iovec iov;
int sock_fd;
int main(int argc, char ** argv)
{
int err;
sock_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_TEST);
if (sock_fd<0) {
char s[BUFSIZ];
sprintf( s, "%s: can't assign fd for socket", argv[0] );
perror(s);
return -1;
}
memset(&src_addr, 0, sizeof(src_addr));
src_addr.nl_family = AF_NETLINK;
src_addr.nl_pid = getpid();
src_addr.nl_groups = 0; // Unicast
//src_addr.nl_groups = RTMGRP_LINK; /* Multicast, bind call always fails for non zero values */
err = bind(sock_fd, (struct sockaddr*)&src_addr, sizeof(src_addr));
perror("bind");
if (err<0) {
char s[BUFSIZ];
sprintf( s, "%s: can't bind socket (%d)and err : %d", argv[0], sock_fd,err );
perror(s);
return -1;
}
memset(&dst_addr, 0, sizeof(dst_addr));
nlh = (struct nlhmsghdr *) malloc(NLMSG_SPACE(MAX_PAYLOAD));
memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD));
iov.iov_base = (void *)nlh;
iov.iov_len = NLMSG_SPACE(MAX_PAYLOAD);
msg.msg_name = (void *)&dst_addr;
msg.msg_namelen = sizeof(dst_addr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
printf("pid : %d\n Waiting for messages from kernel...\n",getpid());
recvmsg(sock_fd, &msg, 0);
printf("Message : %s\n", NLMSG_DATA(nlh));
close(sock_fd);
return 0;
}
Netlink socket binds are sensitive to what USER you are- I've seen them reliably fail if you are not running the program in question as 'root', at least on RedHat 6.
Try running as root 1st, before changing your logic. If you get the same failure as you do in normal operation, then you know it isn't (necessarily) a permissions issue.
The issue is
sock_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_TEST);
Does you kernel module define the NETLINK_TEST family? your own family might must be supported at kernel module and it should post the message in the proper group using nlmsg_multicast()
RTMGRP_LINK is group defined in NETLINK_ROUTE.
This sample code is example for multicast
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#include <unistd.h>
#define MYPROTO NETLINK_USERSOCK
#define MYMGRP 21
int open_netlink(void)
{
int sock;
struct sockaddr_nl addr;
int group = MYMGRP;
sock = socket(AF_NETLINK, SOCK_RAW, MYPROTO);
if (sock < 0) {
printf("sock < 0.\n");
return sock;
}
memset((void *) &addr, 0, sizeof(addr));
addr.nl_family = AF_NETLINK;
addr.nl_pid = getpid();
/* addr.nl_groups = MYMGRP; */
if (bind(sock, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
printf("bind < 0.\n");
return -1;
}
if (setsockopt(sock, 270, NETLINK_ADD_MEMBERSHIP, &group, sizeof(group)) < 0) {
printf("setsockopt < 0\n");
return -1;
}
return sock;
}
void read_event(int sock)
{
struct sockaddr_nl nladdr;
struct msghdr msg;
struct iovec iov;
char buffer[65536];
int ret;
iov.iov_base = (void *) buffer;
iov.iov_len = sizeof(buffer);
msg.msg_name = (void *) &(nladdr);
msg.msg_namelen = sizeof(nladdr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
printf("Ok, listening.\n");
ret = recvmsg(sock, &msg, 0);
if (ret < 0)
printf("ret < 0.\n");
else
printf("Received message payload: %s\n", NLMSG_DATA((struct nlmsghdr *) &buffer));
}
int main(int argc, char *argv[])
{
int nls;
nls = open_netlink();
if (nls < 0)
return nls;
while (1)
read_event(nls);
return 0;
}
kernel module:
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/netlink.h>
#include <net/netlink.h>
#include <net/net_namespace.h>
#define MYPROTO NETLINK_USERSOCK
#define MYGRP 21
static struct sock *nl_sk = NULL;
static void send_to_user(void)
{
struct sk_buff *skb;
struct nlmsghdr *nlh;
char *msg = "Hello from kernel";
int msg_size = strlen(msg) + 1;
int res;
pr_info("Creating skb.\n");
skb = nlmsg_new(NLMSG_ALIGN(msg_size + 1), GFP_KERNEL);
if (!skb) {
pr_err("Allocation failure.\n");
return;
}
nlh = nlmsg_put(skb, 0, 1, NLMSG_DONE, msg_size + 1, 0);
strcpy(nlmsg_data(nlh), msg);
pr_info("Sending skb.\n");
res = nlmsg_multicast(nl_sk, skb, 0, MYGRP, GFP_KERNEL);
if (res < 0)
pr_info("nlmsg_multicast() error: %d\n", res);
else
pr_info("Success.\n");
}
static int __init hello_init(void)
{
pr_info("Inserting hello module.\n");
nl_sk = netlink_kernel_create(&init_net, MYPROTO, NULL);
if (!nl_sk) {
pr_err("Error creating socket.\n");
return -10;
}
send_to_user();
netlink_kernel_release(nl_sk);
return 0;
}
static void __exit hello_exit(void)
{
pr_info("Exiting hello module.\n");
}
module_init(hello_init);
module_exit(hello_exit);
MODULE_LICENSE("GPL");
What is the best possible way to send packets coming on an interface back to the same interface without changing anything in the packet. I want to have a loopback effect for the actual traffic coming on one of my interfaces e.g eth0
I think you can easily achieve this with Python/Scapy. Something like
sniff(iface="eth0", prn=lambda x: sendp(x, iface="eth0"))
should do it.
I don't think you can do this easily with a physical interface. I used the tap module for this purpose, though. It's quite simple: I create a new tap interface, and my program writes back everything that is read from the device. I used this to test a proprietary network protocol - so it might or might not work for what you intend to do. The code is quite simple:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <linux/if_tun.h>
#define DEVNAME "gnlo0"
static int tun_alloc(char *dev)
{
struct ifreq ifr;
int fd, ret;
if ((fd = open("/dev/net/tun", O_RDWR)) < 0) {
perror("open");
return -1;
}
memset(&ifr, 0, sizeof(ifr));
ifr.ifr_flags = IFF_TAP;
if (*dev)
strncpy(ifr.ifr_name, dev, IFNAMSIZ);
ret = ioctl(fd, TUNSETIFF, (void *)&ifr);
if (ret < 0) {
close(fd);
perror("ioctl TUNSETIFF");
return ret;
}
strcpy(dev, ifr.ifr_name);
return fd;
}
int main(int argc, char **argv)
{
int fd = -1;
int ret = 1;
char dev[IFNAMSIZ];
strncpy(dev, DEVNAME, IFNAMSIZ - 1);
printf("opening %s\n", dev);
fd = tun_alloc(dev);
if (fd < 0)
goto out;
char buf[512];
snprintf(buf, sizeof(buf) - 1,
"ip addr flush dev %s; ip link set dev %s up", dev, dev);
if (system(buf) < 0) {
perror("system");
goto out;
}
while (1) {
unsigned char packet[65535];
int len = read(fd, packet, sizeof(packet));
if (len < 0) {
perror("read");
goto out;
}
printf("incoming packet [%d octets]\n", len);
len = write(fd, packet, len);
printf("fed back packet [%d octets]\n", len);
}
ret = 0;
out:
if (fd >= 0)
close(fd);
return ret;
}