linux内核中的文件描述符 二 --socket和文件描述符
linux内核中的文件描述符(二)--socket和文件描述符
Kernel version：2.6.14
CPU architecture：ARM920T
Author：ce123(http://blog.csdn.net/ce123)
socket和文件系统紧密相关，我们可以通过文件系统的open、read、write和close等操作socket。下面是一个简单的例子。
/****************************************************************************//*简介：TCPServer示例 *//****************************************************************************/#include #include #include #include #include #include #include #include int main(int argc, char *argv[]) { int sockfd,new_fd; struct sockaddr_in server_addr; struct sockaddr_in client_addr; int sin_size,portnumber; const char hello[]="Hello\n"; if(argc!=2) { fprintf(stderr,"Usage:%s portnumber\a\n",argv[0]); exit(1); } if((portnumber=atoi(argv[1]))<0) { fprintf(stderr,"Usage:%s portnumber\a\n",argv[0]); exit(1); } /* 服务器端开始建立socket描述符 */ if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1) { fprintf(stderr,"Socket error:%s\n\a",strerror(errno)); exit(1); } /* 服务器端填充 sockaddr结构 */ bzero(&server_addr,sizeof(struct sockaddr_in)); server_addr.sin_family=AF_INET; server_addr.sin_addr.s_addr=htonl(INADDR_ANY); server_addr.sin_port=htons(portnumber); /* 捆绑sockfd描述符 */ if(bind(sockfd,(struct sockaddr *)(&server_addr),sizeof(struct sockaddr))== -1) { fprintf(stderr,"Bind error:%s\n\a",strerror(errno)); exit(1); } /* 监听sockfd描述符 */ if(listen(sockfd,5)==-1) { fprintf(stderr,"Listen error:%s\n\a",strerror(errno)); exit(1); } while(1) { /* 服务器阻塞,直到客户程序建立连接 */ sin_size=sizeof(struct sockaddr_in); if((new_fd=accept(sockfd,(struct sockaddr *)(&client_addr),&sin_size))==-1) { fprintf(stderr,"Accept error:%s\n\a",strerror(errno)); exit(1); } fprintf(stderr,"Server get connection from %s\n", inet_ntoa(client_addr.sin_addr)); if(write(new_fd,hello,strlen(hello))==-1) { fprintf(stderr,"Write Error:%s\n",strerror(errno)); exit(1); } /* 这个通讯已经结束 */ close(new_fd); /* 循环下一个 */ } close(sockfd); exit(0); } 下图说明了socket和fd是怎样联系起来的。
下面通过来具体分析一下。sys_socket是socket相关函数的总入口。
net/socket.c/* * System call vectors. * * Argument checking cleaned up. Saved 20% in size. * This function doesn't need to set the kernel lock because * it is set by the callees. */asmlinkage long sys_socketcall(int call, unsigned long __user *args){ unsigned long a[6]; unsigned long a0,a1; int err; if(call<1||call>SYS_RECVMSG) return -EINVAL; /* copy_from_user should be SMP safe. */ if (copy_from_user(a, args, nargs[call])) return -EFAULT; err = audit_socketcall(nargs[call]/sizeof(unsigned long), a); if (err) return err; a0=a[0]; a1=a[1]; switch(call) { case SYS_SOCKET: err = sys_socket(a0,a1,a[2]); break; case SYS_BIND: err = sys_bind(a0,(struct sockaddr __user *)a1, a[2]); break; case SYS_CONNECT: err = sys_connect(a0, (struct sockaddr __user *)a1, a[2]); break; case SYS_LISTEN: err = sys_listen(a0,a1); break; case SYS_ACCEPT: err = sys_accept(a0,(struct sockaddr __user *)a1, (int __user *)a[2]); break; case SYS_GETSOCKNAME: err = sys_getsockname(a0,(struct sockaddr __user *)a1, (int __user *)a[2]); break; case SYS_GETPEERNAME: err = sys_getpeername(a0, (struct sockaddr __user *)a1, (int __user *)a[2]); break; case SYS_SOCKETPAIR: err = sys_socketpair(a0,a1, a[2], (int __user *)a[3]); break; case SYS_SEND: err = sys_send(a0, (void __user *)a1, a[2], a[3]); break; case SYS_SENDTO: err = sys_sendto(a0,(void __user *)a1, a[2], a[3], (struct sockaddr __user *)a[4], a[5]); break; case SYS_RECV: err = sys_recv(a0, (void __user *)a1, a[2], a[3]); break; case SYS_RECVFROM: err = sys_recvfrom(a0, (void __user *)a1, a[2], a[3], (struct sockaddr __user *)a[4], (int __user *)a[5]); break; case SYS_SHUTDOWN: err = sys_shutdown(a0,a1); break; case SYS_SETSOCKOPT: err = sys_setsockopt(a0, a1, a[2], (char __user *)a[3], a[4]); break; case SYS_GETSOCKOPT: err = sys_getsockopt(a0, a1, a[2], (char __user *)a[3], (int __user *)a[4]); break; case SYS_SENDMSG: err = sys_sendmsg(a0, (struct msghdr __user *) a1, a[2]); break; case SYS_RECVMSG: err = sys_recvmsg(a0, (struct msghdr __user *) a1, a[2]); break; default: err = -EINVAL; break; } return err;} /* It may be already another descriptor 8) Not kernel problem. */ return retval;out_release: sock_release(sock); return retval;}
asmlinkage long sys_socket(int family, int type, int protocol){ int retval; struct socket *sock; retval = sock_create(family, type, protocol, &sock);//创建socket if (retval < 0) goto out; retval = sock_map_fd(sock);//分配一个未使用的文件描述符fd，并将socket和fd建立联系 if (retval < 0) goto out_release;out: /* It may be already another descriptor 8) Not kernel problem. */ return retval;out_release: sock_release(sock); return retval;}struct socket { socket_state state; unsigned long flags; struct proto_ops *ops; struct fasync_struct *fasync_list; struct file *file;//通过这个和文件描述符建立联系 struct sock *sk; wait_queue_head_t wait; short type;};int sock_map_fd(struct socket *sock){ int fd; struct qstr this; char name[32]; /* * Find a file descriptor suitable for return to the user. */ fd = get_unused_fd();//分配一个未使用的fd if (fd >= 0) { struct file *file = get_empty_filp(); if (!file) { put_unused_fd(fd); fd = -ENFILE; goto out; } this.len = sprintf(name, "[%lu]", SOCK_INODE(sock)->i_ino); this.name = name; this.hash = SOCK_INODE(sock)->i_ino; file->f_dentry = d_alloc(sock_mnt->mnt_sb->s_root, &this); if (!file->f_dentry) { put_filp(file); put_unused_fd(fd); fd = -ENOMEM; goto out; } file->f_dentry->d_op = &sockfs_dentry_operations; d_add(file->f_dentry, SOCK_INODE(sock)); file->f_vfsmnt = mntget(sock_mnt); file->f_mapping = file->f_dentry->d_inode->i_mapping; sock->file = file;//建立联系 file->f_op = SOCK_INODE(sock)->i_fop = &socket_file_ops;//socket操作函数，当使用文件系统的IO函数时，其实使用的是socket的IO函数 file->f_mode = FMODE_READ | FMODE_WRITE; file->f_flags = O_RDWR; file->f_pos = 0; file->private_data = sock; fd_install(fd, file); }out: return fd;}static struct file_operations socket_file_ops = { .owner = THIS_MODULE, .llseek = no_llseek, .aio_read = sock_aio_read, .aio_write = sock_aio_write, .poll = sock_poll, .unlocked_ioctl = sock_ioctl, .mmap = sock_mmap, .open = sock_no_open, /* special open code to disallow open via /proc */ .release = sock_close, .fasync = sock_fasync, .readv = sock_readv, .writev = sock_writev, .sendpage = sock_sendpage};再分享一下我老师大神的人工智能教程吧。零基础！通俗易懂！风趣幽默！还带黄段子！希望你也加入到我们人工智能的队伍中来！https://blog.csdn.net/jiangjunshow