Function dd_copy

src/dd.c:2085–2370

/* The main loop.  */

static int
dd_copy (void)
{
  char *bufstart;		/* Input buffer. */
  ssize_t nread;		/* Bytes read in the current block.  */

  /* If nonzero, then the previously read block was partial and
     PARTREAD was its size.  */
  idx_t partread = 0;

  int exit_status = EXIT_SUCCESS;
  idx_t n_bytes_read;

  if (skip_records != 0 || skip_bytes != 0)
    {
      intmax_t us_bytes;
      bool us_bytes_overflow =
        (ckd_mul (&us_bytes, skip_records, input_blocksize)
         || ckd_add (&us_bytes, skip_bytes, us_bytes));
      off_t input_offset0 = input_offset;
      intmax_t us_blocks = skip (STDIN_FILENO, input_file,
                                 skip_records, input_blocksize, &skip_bytes);

      /* POSIX doesn't say what to do when dd detects it has been
         asked to skip past EOF, so I assume it's non-fatal.
         There are 3 reasons why there might be unskipped blocks/bytes:
             1. file is too small
             2. pipe has not enough data
             3. partial reads  */
      if ((us_blocks
           || (0 <= input_offset
               && (us_bytes_overflow
                   || us_bytes != input_offset - input_offset0)))
          && status_level != STATUS_NONE)
        {
          diagnose (0, _("%s: cannot skip to specified offset"),
                    quotef (input_file));
        }
    }

  if (seek_records != 0 || seek_bytes != 0)
    {
      idx_t bytes = seek_bytes;
      intmax_t write_records = skip (STDOUT_FILENO, output_file,
                                      seek_records, output_blocksize, &bytes);

      if (write_records != 0 || bytes != 0)
        {
          memset (obuf, 0, write_records ? output_blocksize : bytes);

          do
            {
              idx_t size = write_records ? output_blocksize : bytes;
              if (iwrite (STDOUT_FILENO, obuf, size) != size)
                {
                  diagnose (errno, _("writing to %s"), quoteaf (output_file));
                  quit (EXIT_FAILURE);
                }