微控制器具有非常简单的IP堆栈,因此mc发送UDP数据包的最简单方法是广播它们.

在PC端,我想接收广播,但只能从eth1接收.所以我试图将UDP套接字绑定到eth1设备.

问题(源代码如下)：

> setsockopt(sock,SOL_SOCKET,SO_BINDTODEVICE,device,sizeof(device))需要root权限,为什么？ (设置其他选项作为用户)
> getsockopt(sock,(void *)buffer,& opt_length)给出“协议不可用”.我想通过setsockopt命令读回我设置的设备.
>哪里可以找到好的信息？我检查了一些Linux编程,网络书籍,但例如我只在互联网上找到的SO_BINDTODEVICE选项.

我的冗长(脏)测试程序显示问题.设置并返回SO_RCVTIMEO和SO_BROADCAST选项的工作原理.

以用户身份运行代码：

could not set SO_BINDTODEVICE (Operation not permitted)"

运行sudo给出：

SO_BINDTODEVICE set
./mc-test: could not get SO_BINDTODEVICE (Protocol not available)

所以,设置选项似乎工作,但读回是不可能的？

/* SO_BINDTODEVICE test */ 

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <sys/time.h>
#include <errno.h>

#define MC_IP "192.168.7.2"
#define MC_PORT (54321)
#define MY_PORT (54321)
#define MY_DEVICE "eth1"

#define BUFFERSIZE (1000)

/* global variables */
int sock;
struct sockaddr_in MC_addr;
struct sockaddr_in my_addr;
char buffer[BUFFERSIZE];

int main(int argc,char *argv[]) 
{
  unsigned int echolen,clientlen;
  int rc,n;
  char opt_buffer[1000];
  struct protoent *udp_protoent;
  struct timeval receive_timeout;
  int optval;
  socklen_t opt_length;

  /* Create the UDP socket */
  if ((sock = socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP)) < 0) 
  {
    printf ("%s: Failed to create UDP socket (%s) \n",argv[0],strerror(errno));
    exit (EXIT_FAILURE);
  }
  printf ("UDP socket created\n");

  /* set the recvfrom timeout value */
  receive_timeout.tv_sec = 5;
  receive_timeout.tv_usec = 0;
  rc=setsockopt(sock,SO_RCVTIMEO,&receive_timeout,sizeof(receive_timeout));
  if (rc != 0) 
  {
     printf ("%s: could not set SO_RCVTIMEO (%s)\n",strerror(errno));
     exit (EXIT_FAILURE);
  }
  printf ("set timeout to\ntime [s]: %d\ntime [ms]: %d\n",receive_timeout.tv_sec,receive_timeout.tv_usec);
  /* verify the recvfrom timeout value */
  rc=getsockopt(sock,&opt_length);
  if (rc != 0) 
  {
     printf ("%s: could not get socket options (%s)\n",strerror(errno));
     exit (EXIT_FAILURE);
  }
  printf ("timeout value\ntime [s]: %d\ntime [ms]: %d\n",receive_timeout.tv_usec);

  /* allow broadcast messages for the socket */
  int true = 1;
  rc=setsockopt(sock,SO_BROADCAST,&true,sizeof(true));
  if (rc != 0) 
  {
     printf ("%s: could not set SO_BROADCAST (%s)\n",strerror(errno));
     exit (EXIT_FAILURE);
  }
  printf ("set SO_BROADCAST\n");
  /* verify SO_BROADCAST setting */
  rc=getsockopt(sock,&optval,&opt_length);
  if (optval != 0) 
  {
    printf("SO_BROADCAST is enabled\n");
  }

  /* bind the socket to one network device */
  const char device[] = MY_DEVICE;
  rc=setsockopt(sock,sizeof(device));
  if (rc != 0) 
  {
     printf ("%s: could not set SO_BINDTODEVICE (%s)\n",strerror(errno));
     exit (EXIT_FAILURE);
  }
  printf ("SO_BINDTODEVICE set\n");
  /* verify SO_BINDTODEVICE setting */
  rc = getsockopt(sock,&opt_length);
  if (rc != 0) 
  {
     printf ("%s: could not get SO_BINDTODEVICE (%s)\n",strerror(errno));
     exit (EXIT_FAILURE);
  }
  if (rc == 0) 
  {
    printf("SO_BINDTODEVICE is: %s\n",buffer);
  }


  /* Construct the server sockaddr_in structure */
  memset(&MC_addr,sizeof(MC_addr));     /* Clear struct */
  MC_addr.sin_family = AF_INET;         /* Internet/IP */
  MC_addr.sin_addr.s_addr = inet_addr(MC_IP);   /* IP address */
  MC_addr.sin_port = htons(MC_PORT);        /* server port */

  /* bind my own Port */
  my_addr.sin_family = AF_INET;
  my_addr.sin_addr.s_addr = INADDR_ANY; /* INADDR_ANY all local addresses */
  my_addr.sin_port = htons(MY_PORT);
  rc = bind (sock,(struct sockaddr *) &my_addr,sizeof(my_addr));
  if (rc < 0) 
  {
     printf ("%s: could not bind port (%s)\n",strerror(errno));
     exit (EXIT_FAILURE);
  }
  printf ("port bound\n");

  /* identify mc */
  buffer[0] = (char)1;
  buffer[1] = (char)0;
  send_data (buffer,2);  
  printf ("sent command: %d\n",(char)buffer[0]);

  rc=receive_data(buffer);
  printf ("%d bytes received\n",rc);
  buffer[rc] = (char)0; /* string end symbol */
  printf ("%d - %s\n",(int)(char)buffer[0],&buffer[1]);

  close(sock);
  printf ("socket closed\n");

  exit(0);
}

/* send data to the MC *****************************************************/
/* buffer points to the bytes to send */
/* buf_length is the number of bytes to send */
/* returns allways 0 */
int send_data( char *buffer,int buf_length )
{
  int rc;

  rc = sendto (sock,buffer,buf_length,(struct sockaddr *) &MC_addr,sizeof(MC_addr));
  if (rc < 0) 
  {
    printf ("could not send data\n");
    close (sock);
    exit (EXIT_FAILURE);
  }
  return(0);
}

/* receive data from the MC *****************************************************/
/* buffer points to the memory for the received data */
/* max BUFFERSIZE bytes can be received */
/* returns number of bytes received */
int receive_data(char *buffer)
{
  int rc,MC_addr_length;

  MC_addr_length = sizeof(MC_addr);
  rc = recvfrom (sock,BUFFERSIZE,&MC_addr_length);
  if (rc < 0) 
  {
    printf ("could not receive data\n");
    close (sock);
    exit (EXIT_FAILURE);
  }
  return(rc);
}