Merge "Adjust the size limit for splitting large files" into mnc-dr-dev

      too many blocks (greater than MAX_BLOCKS_PER_DIFF_TRANSFER), we split it

      into smaller pieces by getting multiple Transfer()s.

      The downside is that after splitting, we can no longer use imgdiff but

      only bsdiff."""

      MAX_BLOCKS_PER_DIFF_TRANSFER = 1024

      The downside is that after splitting, we may increase the package size

      since the split pieces don't align well. According to our experiments,

      1/8 of the cache size as the per-piece limit appears to be optimal.

      Compared to the fixed 1024-block limit, it reduces the overall package

      size by 30% volantis, and 20% for angler and bullhead."""

      # We care about diff transfers only.

      if style != "diff" or not split:

        Transfer(tgt_name, src_name, tgt_ranges, src_ranges, style, by_id)

        return

      pieces = 0

      cache_size = common.OPTIONS.cache_size

      split_threshold = 0.125

      max_blocks_per_transfer = int(cache_size * split_threshold /

                                    self.tgt.blocksize)

      # Change nothing for small files.

      if (tgt_ranges.size() <= MAX_BLOCKS_PER_DIFF_TRANSFER and

          src_ranges.size() <= MAX_BLOCKS_PER_DIFF_TRANSFER):

      if (tgt_ranges.size() <= max_blocks_per_transfer and

          src_ranges.size() <= max_blocks_per_transfer):

        Transfer(tgt_name, src_name, tgt_ranges, src_ranges, style, by_id)

        return

      pieces = 0

      while (tgt_ranges.size() > MAX_BLOCKS_PER_DIFF_TRANSFER and

             src_ranges.size() > MAX_BLOCKS_PER_DIFF_TRANSFER):

      while (tgt_ranges.size() > max_blocks_per_transfer and

             src_ranges.size() > max_blocks_per_transfer):

        tgt_split_name = "%s-%d" % (tgt_name, pieces)

        src_split_name = "%s-%d" % (src_name, pieces)

        tgt_first = tgt_ranges.first(MAX_BLOCKS_PER_DIFF_TRANSFER)

        src_first = src_ranges.first(MAX_BLOCKS_PER_DIFF_TRANSFER)

        tgt_first = tgt_ranges.first(max_blocks_per_transfer)

        src_first = src_ranges.first(max_blocks_per_transfer)

        Transfer(tgt_split_name, src_split_name, tgt_first, src_first, style,

                 by_id)