cat_noblock.c

对linux内核编程做了详细的解析和举例

/* cat_noblock.c - open a file and display its contents, but exit rather than
 * wait for input */


/* Copyright (C) 1998 by Ori Pomerantz */



#include <stdio.h>    /* standard I/O */
#include <fcntl.h>    /* for open */
#include <unistd.h>   /* for read */ 
#include <stdlib.h>   /* for exit */
#include <errno.h>    /* for errno */

#define MAX_BYTES 1024*4


main(int argc, char *argv[])
{
  int    fd;  /* The file descriptor for the file to read */
  size_t bytes; /* The number of bytes read */
  char   buffer[MAX_BYTES]; /* The buffer for the bytes */  


  /* Usage */
  if (argc != 2) {
    printf("Usage: %s <filename>\n", argv[0]);
    puts("Reads the content of a file, but doesn't wait for input");
    exit(-1);
  }

  /* Open the file for reading in non blocking mode */ 
  fd = open(argv[1], O_RDONLY | O_NONBLOCK);

  /* If open failed */
  if (fd == -1) {
    if (errno = EAGAIN)
      puts("Open would block");
    else
      puts("Open failed");
    exit(-1);
  }

  /* Read the file and output its contents */
  do {
    int i;

    /* Read characters from the file */
    bytes = read(fd, buffer, MAX_BYTES);

    /* If there's an error, report it and die */
    if (bytes == -1) {
      if (errno = EAGAIN)
	puts("Normally I'd block, but you told me not to");
      else
	puts("Another read error");
      exit(-1);
    }

    /* Print the characters */
    if (bytes > 0) {
      for(i=0; i<bytes; i++)
	putchar(buffer[i]);
    }

    /* While there are no errors and the file isn't over */
  } while (bytes > 0);
}