#define _LARGEFILE64_SOURCE /* See feature_test_macros(7) */
#include <stdio.h>
#include <errno.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <limits.h>

#define SECTOR_SIZE 512

/*
Writes a test pattern, 1 sector in size, to a disk. Careful: destructive!

lseek64 allows the use of very long offsets.
Specifying _LARGEFILE64_SOURCE is required for off_t used by lseek
to be of 64 bit.

for more infos:
$ man 3 lseek64
*/

int writelba(int fd, long offset, char* buf, int buf_size){
    //write to fd at offset and sync

    lseek64(fd, offset, SEEK_SET);
    if (errno > 0) return errno;
    write(fd, buf, buf_size);
    if (errno > 0) return errno;

    sync(); //to make sure it isn't cached in RAM

    return errno;
}

int readlba(int fd, long offset, char* buf, int buf_size){
    //read from fd at offset

    lseek64(fd, offset, SEEK_SET);
    if (errno > 0) return errno;

    read(fd, buf, buf_size);
    if (errno > 0) return errno;

    return errno;
}

int main (void){
    int fd;
    char buf[SECTOR_SIZE] = {0};
    memset(&buf, 0x64, sizeof(buf)/sizeof(char)); //initalise buf with a pattern
    char result[SECTOR_SIZE] = {0};
    int error = 0;
    long sector = 1306638144;
    long offset = sector*SECTOR_SIZE; //seek offset works with bytes

    fd = open("/dev/sdb", O_RDWR);
    if (fd < 0){
        printf("Failed opening file descriptor: %d", errno);
        exit(errno);
    }

    printf("Testing sector: %ld\n", sector);

    error = writelba(fd, offset, buf, sizeof(buf)/sizeof(char));
    if (error > 0){
        printf("Error while writing: %d\n", error);
        exit(error);
    }

    error = readlba(fd, offset, result, sizeof(result)/sizeof(char));
    if (error > 0){
        printf("Error while reading: %d\n", error);
        exit(error);
    }

    //print out what was read
    printf("test pattern: %02x\nresult:\n", buf[0]);
    for(int i = 0; i < 512; i++){
        printf("%02x ", result[i]);
    }
    printf("\n");

    //to externally check this result: dd if=/dev/sdb of=/tmp/bin bs=512 count=1 skip=<LBA> && xxd /tmp/bin


    exit(0);
}