进程间传递文件描述符例子程序

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>

#include <sys/socket.h> /* for socketpair */

#define MY_LOGO "Micheal"

/*
* 从fd中接收消息，并将文件描述符放在指针recvfd中
*/
ssize_t recv_fd(int fd, void*data, size_t bytes, int*recvfd)
{
  struct msghdr msghdr_recv; /*接收消息接收*/
  struct iovec iov[1]; /*接收数据的向量*/
  size_t n;
  int newfd;

  union{
    struct cmsghdr cm;
    char control[CMSG_SPACE(sizeof(int))];
  }control_un;
  struct cmsghdr*pcmsghdr; /*消息头部*/
  msghdr_recv.msg_control = control_un.control; /*控制消息*/
  msghdr_recv.msg_controllen = sizeof(control_un.control); /*控制消息的长度*/

  msghdr_recv.msg_name = NULL; /*消息的名称为空*/
  msghdr_recv.msg_namelen = 0; /*消息的长度为空*/

  iov[0].iov_base = data; /*向量的数据为传入的数据*/
  iov[0].iov_len = bytes; /*向量的长度为传入数据的长度*/
  msghdr_recv.msg_iov = iov; /*消息向量指针*/
  msghdr_recv.msg_iovlen = 1; /*消息向量的个数为1个*/
  if((n = recvmsg(fd, &msghdr_recv, 0))<=0) /*接收消息*/
    return n;

  if((pcmsghdr = CMSG_FIRSTHDR(&msghdr_recv))!= NULL && /*获得消息的头部*/
      pcmsghdr->cmsg_len == CMSG_LEN(sizeof(int))) { /*获得消息的长度为int*/
    if(pcmsghdr->cmsg_level != SOL_SOCKET) /*消息的level应该为SOL_SOCKET*/
      printf("control level != SOL_SOCKET\n");

    if(pcmsghdr->cmsg_type != SCM_RIGHTS) /*消息的类型判断*/
      printf("control type != SCM_RIGHTS\n");

    *recvfd =*((int*)CMSG_DATA(pcmsghdr)); /*获得打开文件的描述符*/
  } else
    *recvfd = -1;

  return n; /*返回接收消息的长度*/
}


ssize_t send_fd(int fd, void*data, size_t bytes, int sendfd)
{
  struct msghdr msghdr_send; /*发送消息*/
  struct iovec iov[1]; /*向量*/
  size_t n; /*大小*/
  int newfd; /*文件描述符*/
  /*方便操作msg的结构*/
  union{
    struct cmsghdr cm; /*control msg结构*/
    char control[CMSG_SPACE(sizeof(int))]; /*字符指针，方便控制*/
  }control_un;
  struct cmsghdr*pcmsghdr=NULL; /*控制头部的指针*/
  msghdr_send.msg_control = control_un.control; /*控制消息*/
  msghdr_send.msg_controllen = sizeof(control_un.control); /*长度*/

  pcmsghdr = CMSG_FIRSTHDR(&msghdr_send); /*取得第一个消息头*/
  pcmsghdr->cmsg_len = CMSG_LEN(sizeof(int)); /*获得长度*/
  pcmsghdr->cmsg_level = SOL_SOCKET; /*用于控制消息*/
  pcmsghdr->cmsg_type = SCM_RIGHTS;
  *((int*)CMSG_DATA(pcmsghdr))= sendfd; /*socket值*/


  msghdr_send.msg_name = NULL; /*名称*/
  msghdr_send.msg_namelen = 0; /*名称长度*/

  iov[0].iov_base = data; /*向量指针*/
  iov[0].iov_len = bytes; /*数据长度*/
  msghdr_send.msg_iov = iov; /*填充消息*/
  msghdr_send.msg_iovlen = 1;

  return (sendmsg(fd, &msghdr_send, 0)); /*发送消息*/
}


int main()
{
  pid_t pid;
  int sockpair[2];
  int rv;
  char fname[256];
  int fd;
  char rev,sen;

  rv = socketpair(AF_UNIX, SOCK_STREAM, 0, sockpair);
  if (rv < 0) {
    printf("Call socketpair error, errno is %d\n", errno);
    return errno;
  }

  pid = fork();
  if (pid == 0) {
    /* in child */
    close(sockpair[1]);

    for ( ; ; ) {
      //fd = recv_fd(sockpair[0]);

      recv_fd(sockpair[0],&rev,1,&fd);

      if (fd < 0) {
        printf("[CHILD]: child process exit normally!\n");
        break;
      }

      /* 处理fd描述符对应的文件 */
      rv = write(fd, MY_LOGO, strlen(MY_LOGO));
      if (rv < 0) {
        printf("[CHILD]: write error, errno is %d\n", rv);
      } else {
        printf("[CHILD]: append logo successfully\n");
      }
      close(fd);
    }
    exit(0);
  }
  /* in parent */
  for ( ; ; ) {
    memset(fname, 0, sizeof(fname));
    printf("[PARENT]: please enter filename:\n");
    scanf("%s", fname);

    // if (strcmp(fname, "exit") == 0) {

    // rv = send_fd(sockpair[1], -1);

    // if (rv < 0) {

    // printf("[PARENT]: send_fd error, errno is %d\n", rv);

    // }

    // break;

    // }


    fd = open(fname, O_RDWR | O_APPEND);
    if (fd < 0) {
      if (errno == ENOENT) {
        printf("[PARENT]: can't find file '%s'\n", fname);
        continue;
      }
      printf("[PARENT]: open file error, errno is %d\n", errno);
    }
    //rv = send_fd(sockpair[1], fd);

    send_fd(sockpair[1],"",1,fd);
    if (rv != 0) {
      printf("[PARENT]: send_fd error, errno is %d\n", rv);
    }
    //close(fd);

    rv = write(fd, "PARENT write\n", strlen("PARENT write\n"));
    if (rv < 0) {
      printf("[PARENT]: write error, errno is %d\n", rv);
    } else {
      printf("[PARENT]: append logo successfully\n");
    }
  }
  wait(NULL);
  return 0;
}