Merge "Avoid writing too much new data per transfer" into nyc-mr1-dev

    return ctx.hexdigest()

  def WriteTransfers(self, prefix):

    def WriteTransfersZero(out, to_zero):

      """Limit the number of blocks in command zero to 1024 blocks.

    def WriteSplitTransfers(out, style, target_blocks):

      """Limit the size of operand in command 'new' and 'zero' to 1024 blocks.

      This prevents the target size of one command from being too large; and

      might help to avoid fsync errors on some devices."""

      zero_blocks_limit = 1024

      assert (style == "new" or style == "zero")

      blocks_limit = 1024

      total = 0

      while to_zero:

        zero_blocks = to_zero.first(zero_blocks_limit)

        out.append("zero %s\n" % (zero_blocks.to_string_raw(),))

        total += zero_blocks.size()

        to_zero = to_zero.subtract(zero_blocks)

      while target_blocks:

        blocks_to_write = target_blocks.first(blocks_limit)

        out.append("%s %s\n" % (style, blocks_to_write.to_string_raw()))

        total += blocks_to_write.size()

        target_blocks = target_blocks.subtract(blocks_to_write)

      return total

    out = []

      if xf.style == "new":

        assert xf.tgt_ranges

        out.append("%s %s\n" % (xf.style, xf.tgt_ranges.to_string_raw()))

        assert tgt_size == WriteSplitTransfers(out, xf.style, xf.tgt_ranges)

        total += tgt_size

      elif xf.style == "move":

        assert xf.tgt_ranges

      elif xf.style == "zero":

        assert xf.tgt_ranges

        to_zero = xf.tgt_ranges.subtract(xf.src_ranges)

        assert WriteTransfersZero(out, to_zero) == to_zero.size()

        assert WriteSplitTransfers(out, xf.style, to_zero) == to_zero.size()

        total += to_zero.size()

      else:

        raise ValueError("unknown transfer style '%s'\n" % xf.style)

    # Zero out extended blocks as a workaround for bug 20881595.

    if self.tgt.extended:

      assert (WriteTransfersZero(out, self.tgt.extended) ==

      assert (WriteSplitTransfers(out, "zero", self.tgt.extended) ==

              self.tgt.extended.size())

      total += self.tgt.extended.size()