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/*

 * wrtmbr.c -- write the master boot record to the disk

 */

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <stdarg.h>

#define SECTOR_SIZE             512

void error(char *fmt, ...) {

  va_list ap;

  va_start(ap, fmt);

  fprintf(stderr, "Error: ");

  vfprintf(stderr, fmt, ap);

  fprintf(stderr, "\n");

  va_end(ap);

  exit(1);

}

void usage(char *myself) {

  fprintf(stderr,

          "Usage: %s <disk file> <master boot record file>\n",

          myself);

  exit(1);

}

int main(int argc, char *argv[]) {

  FILE *diskFile;

  FILE *bootFile;

  unsigned char sectorBuffer[SECTOR_SIZE];

  if (argc != 3) {

    usage(argv[0]);

  }

  diskFile = fopen(argv[1], "r+b");

  if (diskFile == NULL) {

    error("cannot open disk file '%s'", argv[1]);

  }

  bootFile = fopen(argv[2], "rb");

  if (bootFile == NULL) {

    error("cannot open boot sector file '%s'", argv[2]);

  }

  if (fseek(bootFile, 0, SEEK_END) != 0) {

    error("cannot position to end of boot sector file");

  }

  if (ftell(bootFile) != SECTOR_SIZE) {

    error("'%s' is not a proper boot sector file (wrong length)", argv[2]);

  }

  if (fseek(bootFile, 0, SEEK_SET) != 0) {

    error("cannot position to start of boot sector file");

  }

  if (fread(sectorBuffer, SECTOR_SIZE, 1, bootFile) != 1) {

    error("cannot read data from boot sector file");

  }

  fclose(bootFile);

  if (sectorBuffer[SECTOR_SIZE - 2] != 0x55 ||

      sectorBuffer[SECTOR_SIZE - 1] != 0xAA) {

    error("'%s' is not a proper boot sector file (no signature)", argv[2]);

  }

  if (fseek(diskFile, 0, SEEK_SET) != 0) {

    error("cannot position to start of disk file");

  }

  if (fwrite(sectorBuffer, 1, SECTOR_SIZE, diskFile) != SECTOR_SIZE) {

    error("cannot write boot sector to disk file");

  }

  fclose(diskFile);

  return 0;

}