高级I/O函数pipe,dup,readv,splice,sendfile,tee,fcntl

pipe函数

用于创建一个管道，实现进程间通信。

#include<unistd.h>

int pipe(int fd[2]);

 dup函数和dup2函数

有时我们希望把标准输入重定向到一个文件，或者把标准输出重定向到一个网络连接（比如CGI编程），可以通过dup和dup2实现

 看个例子：

server.c

#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<signal.h>
#include<unistd.h>
#include<stdlib.h>
#include<assert.h>
#include<stdio.h>
#include<errno.h>
#include<string.h>
#include<stdbool.h>
#include<libgen.h>
const int BUFFER_SIZE=1024;
int main(int argc,char* argv[])
{if(argc<=2){printf("usage: %s ip_address port_number\n",basename(argv[0]));return 1;}const char* ip=argv[1];int port=atoi(argv[2]);int sock=socket(PF_INET,SOCK_STREAM,0);assert(sock>=0);// 创建一个ipv4地址struct sockaddr_in address;bzero(&address,sizeof(address));address.sin_family=AF_INET;inet_pton(AF_INET,ip,&address.sin_addr);address.sin_port=htons(port);int  ret=bind(sock,(struct sockaddr*)&address,sizeof(address));assert(ret!=-1);ret=listen(sock,5);assert(ret!=-1);struct sockaddr_in client;socklen_t client_addrlength=sizeof(client);int connfd=accept(sock,(struct sockaddr*)&client,&client_addrlength);if(connfd<0){printf("errno is: %d\n",errno);}else{close(STDOUT_FILENO);dup(connfd);printf("abcd\n");close(connfd);}close(sock);return 0;
}

client.c

#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<signal.h>
#include<unistd.h>
#include<stdlib.h>
#include<assert.h>
#include<stdio.h>
#include<errno.h>
#include<string.h>
#include<stdbool.h>
#include<libgen.h>
const int BUFFER_SIZE=512;
int main(int argc,char* argv[])
{if(argc<=2){printf("usage: %s ip_address port_number send_buffer_size\n",basename(argv[0]));return 1;}const char* ip=argv[1];int port=atoi(argv[2]);int sockfd=socket(PF_INET,SOCK_STREAM,0);assert(sockfd>=0);// 创建一个ipv4地址struct sockaddr_in server_address;bzero(&server_address,sizeof(server_address));server_address.sin_family=AF_INET;inet_pton(AF_INET,ip,&server_address.sin_addr);server_address.sin_port=htons(port);if(connect(sockfd,(struct sockaddr*)&server_address,sizeof(server_address))<0){printf("connection failed\n");}else{char buffer[BUFFER_SIZE];memset(buffer,'a',BUFFER_SIZE);send(sockfd,buffer,BUFFER_SIZE,0);memset(buffer,'\0',BUFFER_SIZE);int ret=recv(sockfd,buffer,BUFFER_SIZE,0);printf("get %d bytes content:%s\n",ret,buffer);}close(sockfd);return 0;
}

sendfile

sendfile函数在2个文件描述符之间直接传递数据(完全在内核中操作)，从而避免内核缓冲区和用户缓冲区之间的数据拷贝，效率很高，称之为零拷贝。

server.c

#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<signal.h>
#include<unistd.h>
#include<stdlib.h>
#include<assert.h>
#include<stdio.h>
#include<errno.h>
#include<string.h>
#include<stdbool.h>
#include<libgen.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<sys/sendfile.h>
const int BUFFER_SIZE=1024;
int main(int argc,char* argv[])
{if(argc<=3){printf("usage: %s ip_address port_number filename\n",basename(argv[0]));return 1;}const char* ip=argv[1];int port=atoi(argv[2]);const char* file_name=argv[3];int filefd=open(file_name,O_RDONLY);assert(filefd>0);struct stat stat_buf;fstat(filefd,&stat_buf);int sock=socket(PF_INET,SOCK_STREAM,0);assert(sock>=0);// 创建一个ipv4地址struct sockaddr_in address;bzero(&address,sizeof(address));address.sin_family=AF_INET;inet_pton(AF_INET,ip,&address.sin_addr);address.sin_port=htons(port);int  ret=bind(sock,(struct sockaddr*)&address,sizeof(address));assert(ret!=-1);ret=listen(sock,5);assert(ret!=-1);struct sockaddr_in client;socklen_t client_addrlength=sizeof(client);int connfd=accept(sock,(struct sockaddr*)&client,&client_addrlength);if(connfd<0){printf("errno is: %d\n",errno);}else{sendfile(connfd,filefd,NULL,stat_buf.st_size);close(connfd);}close(sock);return 0;
}

我用我的电脑telnet服务器，sendfile会把文件内容发送给客户端。

splice函数

splice函数用于在2个文件描述符之间移动数据，也是零拷贝。定义如下：

server.c

#define _GNU_SOURCE 1
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<signal.h>
#include<unistd.h>
#include<stdlib.h>
#include<assert.h>
#include<stdio.h>
#include<errno.h>
#include<string.h>
#include<stdbool.h>
#include<libgen.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<sys/sendfile.h>
const int BUFFER_SIZE=1024;
int main(int argc,char* argv[])
{if(argc<=2){printf("usage: %s ip_address port_number\n",basename(argv[0]));return 1;}const char* ip=argv[1];int port=atoi(argv[2]);int sock=socket(PF_INET,SOCK_STREAM,0);assert(sock>=0);// 创建一个ipv4地址struct sockaddr_in address;bzero(&address,sizeof(address));address.sin_family=AF_INET;inet_pton(AF_INET,ip,&address.sin_addr);address.sin_port=htons(port);int  ret=bind(sock,(struct sockaddr*)&address,sizeof(address));assert(ret!=-1);ret=listen(sock,5);assert(ret!=-1);struct sockaddr_in client;socklen_t client_addrlength=sizeof(client);int connfd=accept(sock,(struct sockaddr*)&client,&client_addrlength);if(connfd<0){printf("errno is: %d\n",errno);}else{int pipefd[2];assert(ret!=-1);ret=pipe(pipefd);//创建管道// 将connfd上流入的客户数据定向到管道中ret=splice(connfd,NULL,pipefd[1],NULL,32768,SPLICE_F_MORE | SPLICE_F_MOVE);assert(ret!=-1);// 将管道的输出定向到connfd客户连接文件描述符ret=splice(pipefd[0],NULL,connfd,NULL,32768,SPLICE_F_MORE | SPLICE_F_MOVE);assert(ret!=-1);close(connfd);}close(sock);return 0;
}

 client.c

#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<signal.h>
#include<unistd.h>
#include<stdlib.h>
#include<assert.h>
#include<stdio.h>
#include<errno.h>
#include<string.h>
#include<stdbool.h>
#include<libgen.h>
const int BUFFER_SIZE=512;
int main(int argc,char* argv[])
{if(argc<=2){printf("usage: %s ip_address port_number send_buffer_size\n",basename(argv[0]));return 1;}const char* ip=argv[1];int port=atoi(argv[2]);int sockfd=socket(PF_INET,SOCK_STREAM,0);assert(sockfd>=0);// 创建一个ipv4地址struct sockaddr_in server_address;bzero(&server_address,sizeof(server_address));server_address.sin_family=AF_INET;inet_pton(AF_INET,ip,&server_address.sin_addr);server_address.sin_port=htons(port);if(connect(sockfd,(struct sockaddr*)&server_address,sizeof(server_address))<0){printf("connection failed\n");}else{char buffer[BUFFER_SIZE];memset(buffer,'a',BUFFER_SIZE);send(sockfd,buffer,BUFFER_SIZE,0);memset(buffer,'\0',BUFFER_SIZE);int ret=recv(sockfd,buffer,BUFFER_SIZE,0);printf("get %d bytes content:%s\n",ret,buffer);}close(sockfd);return 0;
}

fcntl函数

正如其名字（file control)描述那样，提供了对文件描述符的各种控制操作。另一个常见的控制文件描述符属性和行为的系统调用是ioctl，而且ioctl比fcntl能够执行更多的控制。但是对于控制文件描述符常用的属性和行为，fcntl函数是由POSIX规范指定的首选方法。定义如下：