linux编程文件描述符传递

有一种TCP处理方式是，有一个进程专门来复制端口的监听，然后将接收到得tcp连接交由其余的进程来处理，那么这里就涉及到了文件描述符的传递问题了。。。其实实现也很简单，无非就是accept进程向另外的进程发送一些消息，让它的文件描述表中生成新的一项，然后指向刚刚接受的文件描述符表项就可以了。。。同时监听进程也可以close掉刚刚接收的文件描述符，因为已经有新的进程接管了。。。。

这里记录代码：

#include "../core/core.h"

int send_fd(int sock, int fd)  
{  
    struct iovec iov[1];  
    char c = 0;  
    iov[0].iov_base = &c;  
    iov[0].iov_len  = 1;

    int cmsgsize = CMSG_LEN(sizeof(int));  
    struct cmsghdr* cmptr = (struct cmsghdr*)malloc(cmsgsize);  
    if(cmptr == NULL){  
        return -1;  
    }  
    cmptr->cmsg_level = SOL_SOCKET;  
    cmptr->cmsg_type = SCM_RIGHTS; // we are sending fd.  
    cmptr->cmsg_len = cmsgsize;  

    struct msghdr msg;  
    msg.msg_iov = iov;  
    msg.msg_iovlen = 1;  
    msg.msg_name = NULL;  
    msg.msg_namelen = 0;  
    msg.msg_control = cmptr;  
    msg.msg_controllen = cmsgsize;  
    *(int *)CMSG_DATA(cmptr) = fd;  

    int ret = sendmsg(sock, &msg, 0);  
    free(cmptr);  
    if (ret == -1){  
return -1;  
    }  
return 0;
}  

int recv_fd(int sock)  
{ 
    int cmsgsize = CMSG_LEN(sizeof(int));  
    struct cmsghdr* cmptr = (struct cmsghdr*)malloc(cmsgsize);  
if (cmptr == NULL) {
return -1;
}
    char buf[32]; // the max buf in msg. 
    struct iovec iov[1];  
    iov[0].iov_base = buf;  
    iov[0].iov_len = sizeof(buf);  
    struct msghdr msg;  
    msg.msg_iov = iov;  
    msg.msg_iovlen  = 1;  
    msg.msg_name = NULL;  
    msg.msg_namelen = 0;  
    msg.msg_control = cmptr;  
    msg.msg_controllen = cmsgsize;  

    int ret = recvmsg(sock, &msg, 0);
    free(cmptr);  
    if (ret == -1) {  
        return -1; 
    }  
int fd = *(int *)CMSG_DATA(cmptr);  
    return fd;  
}