lkmpg/examples/other/cat_noblock.c

/* 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


int 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);
    return 0;
}