Comment 2 for bug 897029

Ah. That's unexpected. /usr/src/linux/Documentation/iostat.txt says this:

"Here are examples of these different formats:
[...]
2.6 diskstats:
   3 0 hda 446216 784926 9550688 4382310 424847 312726 5922052 19310380 0 3376340 23705160
   3 1 hda1 35486 38030 38030 38030
"

and later:

"All merges and timings now happen
at the disk level rather than at both the disk and partition level as
in 2.4. Consequently, you'll see a different statistics output on 2.6 for
partitions from that for disks. There are only *four* fields available
for partitions on 2.6 machines. This is reflected in the examples above.

Field 1 -- # of reads issued
    This is the total number of reads issued to this partition.
Field 2 -- # of sectors read
    This is the total number of sectors requested to be read from this
    partition.
Field 3 -- # of writes issued
    This is the total number of writes issued to this partition.
Field 4 -- # of sectors written
    This is the total number of sectors requested to be written to
    this partition."

pt-diskstats currently only deals with the first one; it's assuming that if it finds a device name, the data will be in the disk format, so when facing something partition-shaped, it saves the number of sectors read as the number of reads merged, and so on; thus, this.

The Perl port was dieing on a malformed line, so I just added a second regex validating this and now it's working as expected:

  #ts device rd_s rd_avkb rd_mb_s rd_mrg rd_cnc rd_rt wr_s wr_avkb wr_mb_s wr_mrg wr_cnc wr_rt busy in_prg
  {9} md0 0.8 4.0 0.0 0% 0.0 0.0 2590.7 4.0 10.1 0% 0.0 0.0 0% 0

(Note that the above is missing the fix for #838939, so it's still half-broken. But that should be enough for this ticket.)