섹터를 찾는 프로그래밍

[bushi@rose net]$ cat test.c
#define _XOPEN_SOURCE 500
#define _LARGEFILE64_SOURCE
 
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
 
#define DEV   "/dev/sda"
#define BUFSZ 10
 
int main()
{
        int fp = open(DEV, O_RDONLY | O_LARGEFILE);
        off64_t res; 
        size_t bytes;
        char buf[BUFSZ];
        int expected_pass, expected_fail;
        int unexpected_pass, unexpected_fail;
 
        if (fp < 0) {
                perror(DEV);
                return EXIT_FAILURE;
        }
 
        errno = 0;
        res = lseek64(fp, 0, SEEK_END);
 
        if (errno) {
                perror(DEV);
                close(fp);
                return EXIT_FAILURE;
 
        }
        printf("%llu\n", res);
 
        expected_pass = 0;
        expected_fail = 0;
        unexpected_pass = 0;
        unexpected_fail = 0;
 
        bytes = pread64(fp, &buf[0], BUFSZ, res - (off64_t)BUFSZ);
        if (bytes == sizeof(buf)) {
                expected_pass ++;
        } else {
                unexpected_fail ++;
        }
 
        bytes = pread64(fp, &buf[0], BUFSZ, res - (off64_t)BUFSZ + 1);
        if (bytes != sizeof(buf)) {
                expected_fail ++;
        } else {
                unexpected_pass ++;
        }
 
        close(fp);
 
        fprintf(stderr, "  expected pass: %d/1\n", expected_pass);
        fprintf(stderr, "  expected fail: %d/1\n", expected_fail);
        fprintf(stderr, "unexpected pass: %d/0\n", unexpected_pass);
        fprintf(stderr, "unexpected fail: %d/0\n", unexpected_fail);
 
        if (unexpected_pass || unexpected_fail) {
                return EXIT_FAILURE;
        }
 
        return EXIT_SUCCESS;
}
[bushi@rose net]$ 
[bushi@rose net]$ gcc -s -o test test.c -Wall
[bushi@rose net]$
[bushi@rose net]$ sudo ./test || echo "Failed"
400088457216
  expected pass: 1/1
  expected fail: 1/1
unexpected pass: 0/0
unexpected fail: 0/0
[bushi@rose net]$