Ubuntu Linux使用Unix域套接字发送文件描述符

我试图发送一个文件描述符与下面粘贴的代码套接字。 此代码来自： http : //www.thomasstover.com/uds.html 。 我在Ubuntu 16.04 64位上运行。

问题是收到我的程序运行的文件描述符是“3”而不是“4”。 在接收过程中，我也无法读取任何数据。 为什么它不工作？

控制台输出如下所示：

Parent at work FILE TO SEND HAS DESCRIPTOR: 4 Parent read: [[hello phil ]] Child at play Read 3! Done: 0 Success! Parent exits 

码：

• Linux中文件描述符的理论极限
• 在用户空间中模拟文件描述符
• 套接字和文件描述符重用（或缺less）
• lsof没有给内置的阅读bash o / p
• Open在不同的进程中返回相同的文件描述符

 #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/socket.h> #include <sys/wait.h> #include <time.h> #include <unistd.h> #include <errno.h> int send_fd(int socket, int fd_to_send) { struct msghdr socket_message; struct iovec io_vector[1]; struct cmsghdr *control_message = NULL; char message_buffer[1]; /* storage space needed for an ancillary element with a paylod of length is CMSG_SPACE(sizeof(length)) */ char ancillary_element_buffer[CMSG_SPACE(sizeof(int))]; int available_ancillary_element_buffer_space; /* at least one vector of one byte must be sent */ message_buffer[0] = 'F'; io_vector[0].iov_base = message_buffer; io_vector[0].iov_len = 1; /* initialize socket message */ memset(&socket_message, 0, sizeof(struct msghdr)); socket_message.msg_iov = io_vector; socket_message.msg_iovlen = 1; /* provide space for the ancillary data */ available_ancillary_element_buffer_space = CMSG_SPACE(sizeof(int)); memset(ancillary_element_buffer, 0, available_ancillary_element_buffer_space); socket_message.msg_control = ancillary_element_buffer; socket_message.msg_controllen = available_ancillary_element_buffer_space; /* initialize a single ancillary data element for fd passing */ control_message = CMSG_FIRSTHDR(&socket_message); control_message->cmsg_level = SOL_SOCKET; control_message->cmsg_type = SCM_RIGHTS; control_message->cmsg_len = CMSG_LEN(sizeof(int)); *((int *) CMSG_DATA(control_message)) = fd_to_send; return sendmsg(socket, &socket_message, 0); } int recv_fd(int socket) { int sent_fd, available_ancillary_element_buffer_space; struct msghdr socket_message; struct iovec io_vector[1]; struct cmsghdr *control_message = NULL; char message_buffer[1]; char ancillary_element_buffer[CMSG_SPACE(sizeof(int))]; /* start clean */ memset(&socket_message, 0, sizeof(struct msghdr)); memset(ancillary_element_buffer, 0, CMSG_SPACE(sizeof(int))); /* setup a place to fill in message contents */ io_vector[0].iov_base = message_buffer; io_vector[0].iov_len = 1; socket_message.msg_iov = io_vector; socket_message.msg_iovlen = 1; /* provide space for the ancillary data */ socket_message.msg_control = ancillary_element_buffer; socket_message.msg_controllen = CMSG_SPACE(sizeof(int)); if(recvmsg(socket, &socket_message, MSG_CMSG_CLOEXEC) < 0) return -1; if(message_buffer[0] != 'F') { /* this did not originate from the above function */ return -1; } if((socket_message.msg_flags & MSG_CTRUNC) == MSG_CTRUNC) { /* we did not provide enough space for the ancillary element array */ return -1; } /* iterate ancillary elements */ for(control_message = CMSG_FIRSTHDR(&socket_message); control_message != NULL; control_message = CMSG_NXTHDR(&socket_message, control_message)) { if( (control_message->cmsg_level == SOL_SOCKET) && (control_message->cmsg_type == SCM_RIGHTS) ) { sent_fd = *((int *) CMSG_DATA(control_message)); return sent_fd; } } return -1; } int main(int argc, char **argv) { const char *filename = "/tmp/z7.c"; if (argc > 1) filename = argv[1]; int sv[2]; if (socketpair(AF_UNIX, SOCK_DGRAM, 0, sv) != 0) fprintf(stderr,"Failed to create Unix-domain socket pair\n"); int pid = fork(); if (pid > 0) // in parent { fprintf(stderr,"Parent at work\n"); close(sv[1]); int sock = sv[0]; int fd = open(filename, O_RDONLY); if (fd < 0) fprintf(stderr,"Failed to open file %s for reading %s\n", filename, strerror(errno)); fprintf(stderr,"FILE TO SEND HAS DESCRIPTOR: %d\n",fd); /* Read some data to demonstrate that file offset is passed */ char buffer[32]; int nbytes = read(fd, buffer, sizeof(buffer)); if (nbytes > 0) fprintf(stderr,"Parent read: [[%.*s]]\n", nbytes, buffer); send_fd(sock, fd); close(fd); sleep(4); fprintf(stderr,"Parent exits\n"); } else // in child { fprintf(stderr,"Child at play\n"); close(sv[0]); int sock = sv[1]; sleep(2); int fd = recv_fd(sock); printf("Read %d!\n", fd); char buffer[256]; ssize_t nbytes; while ((nbytes = read(fd, buffer, sizeof(buffer))) > 0) { fprintf(stderr,"WRITING: %d\n",nbytes); write(1, buffer, nbytes); } printf("Done: %d %s!\n",nbytes,strerror(errno)); close(fd); } return 0; } 

 { echo first cat; cat ; echo second cat ; cat ; } < filename