Sending UDP packets from the Linux Kernel

Question

Even if a similar topic already exists, I noticed that it dates back two years, thus I guess it\'s more appropriate to open a fresh one...

I\'m trying to figure out

Answer 1

Panic during boot might be caused by you trying to use something which wasn't initialized yet. Looking at stack trace might help figuring out what actually happened.

As for you problem, I think you are trying to do a simple thing, so why not stick with simple tools? ;) printks might be bad idea indeed, but give trace_printk a go. trace_printk is part of Ftrace infrastructure.

Section Using trace_printk() in following article should teach you everything you need to know: http://lwn.net/Articles/365835/

Answer 2

I solved my problem a few months ago. Here's the solution I used.

The standard packet-sending API (sock_create, connect, ...) cannot be used in a few contexts (interruptions). Using it in the wrong place leads to a KP.

The netpoll API is more "low-level" and works in every context. However, there are several conditions :

• Ethernet devices
• IP network
• UDP only (no TCP)
• Different computers for sending and receiving packets (You can't send to yourself.)

Make sure to respect them, because you won't get any error message if there's a problem. It will just silently fail :) Here's a bit of code.

Declaration

#include <linux/netpoll.h>
#define MESSAGE_SIZE 1024
#define INADDR_LOCAL ((unsigned long int)0xc0a80a54) //192.168.10.84
#define INADDR_SEND ((unsigned long int)0xc0a80a55) //192.168.10.85
static struct netpoll* np = NULL;
static struct netpoll np_t;

Initialization

np_t.name = "LRNG";
strlcpy(np_t.dev_name, "eth0", IFNAMSIZ);
np_t.local_ip = htonl(INADDR_LOCAL);
np_t.remote_ip = htonl(INADDR_SEND);
np_t.local_port = 6665;
np_t.remote_port = 6666;
memset(np_t.remote_mac, 0xff, ETH_ALEN);
netpoll_print_options(&np_t);
netpoll_setup(&np_t);
np = &np_t;

Use

char message[MESSAGE_SIZE];
sprintf(message,"%d\n",42);
int len = strlen(message);
netpoll_send_udp(np,message,len);

Hope it can help someone.