[PATCH] UBI: Add volume read and write statistics

[per.forlin@xxxxxxxx (Per Förlin)]

> > Am Dienstag, 17. Juli 2018, 17:06:12 CEST schrieb Steve deRosier:
> > > > > While having a cup of coffee I thought more about this.
> > > > > Actually both, MTD and UBI makes sense.
> > > > > The most important issue is that you integrate it with the existing diskstats.
> > > > > So instead of having our own interface feeding MTD/UBI stats into diskstats
> > > > > would be nice. Did you look into that? I'm not sure how much work this would be.
> > > > > That way users can use existing tools such as iostat...
> > > > I actually started out looking for the information under diskstats,
> > > > then I learned it's only for block devices. I took a quick glance at
> > > > it before I went for the sys implementation instead. diskstats is
> > > > separated from the MTD and UBI stuff and I don't know if one can make a
> > > > connection to MTD/UBI somehow. I will take a closer look at this.
> > >
> > > Perhaps it was "only for block devices" because no one ever
> > > implemented the necessary hooks in MTD or UBI?  I don't know the
> > > history, nor the information you found, just making a stab in the
> > > dark.
> > >
> > > If UBI and/or MTD can provide the statistics that diskstats needs in a
> > > interpretation that makes sense, why not go that way?
> >
> > Yeah, that's what I have in mind. Maybe we can easily teach diskstats
> > about MTD.
> Now I got the chance to look at this again. It's not as bad as I thought.
> The diskstats simply takes the block class and iterate over all devices.
> For each device statistics are printed out.
> It should be possible to do the same for the MTD class and the UBI class.
> So far I haven't tested anything just reading code.
> Then it's a matter of taste. Is MTD and UBI stats welcome in genhd.c?
> 
> I will try to find time the coming days or so to make a prove of concept
> implementation to get a better idea of how big the change would be.
I made one observation. The stats in disktats also exists under
/sys/class/block for every device.
Actually it's the stat under /sys that is also available in diskstats.

For instance:
cat /sys/class/block/sda/stat 
220       86    10682      830       14        4      128      110
0      680      940
This format is documented in iostats.txt

The first step could be to only add it under /sys/class/ubi
and /sys/class/mtd.
I'm not sure how to add all these metrics my patch only adds 4 of them.
"Unsupported values" could be set to 0 for now.
I will continue to think about how to integrate with diskstats but
I'm also in favor of adding this support in incremental steps.