Wrong format for /proc/diskstats

[henryx]

As reported in _pslinux.py we have 3 formats for diskstats reporting information:

1. 15 fields if we use a Linux 2.4 kernel;
2. 14 fields if we use a Linux 2.6+ kernel and it reports a partition;
3. 7 fields if we use a Linux 2.6+ kernel and it reports a disk.

In fact, if we use a 2.6+ kernel, we have always a 14 fields structure (I've verified on CentOS 6 and CentOS 7), so the method reports always the same data. Is a good thing to correct this documentation and remove the unused code for cleanup (it also a good thing to check if the data are correct in case of disk or partition check)

[giampaolo]

Mmmm I seem to remember I came up with that code after reading some doc ("man proc" or something) which described those 3 possible formats so I'm not sure it's a good idea to remove it.

[henryx]

Please note: in my issue I've swapped partition and disk, so, as reported in _pslinux.py and in the documentation, in 2.6+ we are 14 fields. But this is a sample output on CentOS 6:

$ uname -r
2.6.32-504.23.4.el6.x86_64
$ cat /proc/diskstats |grep vda
252 0 vda 40894884 762897 4732260326 79610084 32058059 40015556 534598342 81434303 0 80401326 160952373
252 1 vda1 766 349 9776 1421 2004 150893 305806 7859 0 2213 9271
252 2 vda2 40893963 762548 4732249310 79608613 26873238 39864663 534292536 78632222 0 78064225 158150740
$

As noticed, vda (disk) and vda1 (partition) have the same number of fields. At this point, I think that the Linux kernel documentation is outdated

[giampaolo]

I think I'm gonna leave it there just for extra safety: we're not sure whether the Linux doc is outdated.