#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#define ERR_EXIT(m)     do {         perror(m);        exit(EXIT_FAILURE);    }while(0)

void activate_nonblock(int fd);
void deactivate_nonblock(int fd);

int main(int argc, const char *argv[])
{
    activate_nonblock(STDIN_FILENO);
    char buffer[1024] = {0};
    int ret = read(STDIN_FILENO, buffer, 1024);
    if(ret == -1)
        printf("read");
    return 0;
}

void activate_nonblock(int fd)
{
    int ret;
    int flags = fcntl(fd, F_GETFL);
    if(flags == -1)
        ERR_EXIT("fcntl");
    flags |= O_NONBLOCK;
    ret = fcntl(fd, F_SETFL, flags);
    if(ret == -1)
        ERR_EXIT("fcntl");
}

void deactivate_nonblock(int fd)
{
    int ret;
    int flags = fcntl(fd, F_GETFL);
    if(flags == -1)
        ERR_EXIT("fcntl");
    flags &=~O_NONBLOCK;
    ret = fcntl(fd, F_SETFL, flags);
    if(ret == -1)
        ERR_EXIT("fcntl");
}

用fcntl()设置阻塞函数的阻塞性质