Function do_merge_diff

src/tools/rbd/action/MergeDiff.cc:157–407

* Merge two diff files into one single file * Note: It does not do the merging work if * either of the source diff files is stripped, * since which complicates the process and is * rarely used */

 * rarely used
 */
static int do_merge_diff(const char *first, const char *second,
                         const char *path, bool no_progress)
{
  utils::ProgressContext pc("Merging image diff", no_progress);
  int fd = -1, sd = -1, pd = -1, r;

  string f_from, f_to;
  string s_from, s_to;
  uint64_t f_size = 0;
  uint64_t s_size = 0;
  uint64_t pc_size;

  __u8 f_tag = 0, s_tag = 0;
  uint64_t f_off = 0, f_len = 0;
  uint64_t s_off = 0, s_len = 0;
  bool f_end = false, s_end = false;

  bool first_stdin = !strcmp(first, "-");
  if (first_stdin) {
    fd = STDIN_FILENO;
  } else {
    fd = open(first, O_RDONLY|O_BINARY);
    if (fd < 0) {
      r = -errno;
      std::cerr << "rbd: error opening " << first << std::endl;
      goto done;
    }
  }

  sd = open(second, O_RDONLY|O_BINARY);
  if (sd < 0) {
    r = -errno;
    std::cerr << "rbd: error opening " << second << std::endl;
    goto done;
  }

  if (strcmp(path, "-") == 0) {
    pd = 1;
  } else {
    pd = open(path, O_WRONLY | O_CREAT | O_EXCL | O_BINARY, 0644);
    if (pd < 0) {
      r = -errno;
      std::cerr << "rbd: error create " << path << std::endl;
      goto done;
    }
  }

  //We just handle the case like 'banner, [ftag], [ttag], stag, [wztag]*,etag',
  // and the (offset,length) in wztag must be ascending order.
  r = parse_diff_header(fd, &f_tag, &f_from, &f_to, &f_size);
  if (r < 0) {
    std::cerr << "rbd: failed to parse first diff header" << std::endl;
    goto done;
  }

  r = parse_diff_header(sd, &s_tag, &s_from, &s_to, &s_size);
  if (r < 0) {
    std::cerr << "rbd: failed to parse second diff header" << std::endl;