On Feb 22, 2013, at 12:50 PM, James Bottomley 
<james.bottom...@hansenpartnership.com> wrote:

> On Fri, 2013-02-22 at 02:11 +0000, Seymour, Shane M wrote:
>> First forgive me for using outlook for this, if there are any issues with 
>> what I sent let me know and I'll send it again from gmail. This is also my 
>> first attempt at a kernel patch so please be gentle.
>> 
>> This patch was written to enable tape statistics via sysfs for the dt
>> driver based on kernel 3.8.0-rc6. It creates two new files in sysfs
>> and is based on work done previously in 2005 by Kai Mäkisara. Any
>> feedback would be greatly appreciated.
> 
> I'm afraid we can't do it the way you're proposing.  files in sysfs must
> conform to the one value per file rule (so we avoid the ABI nastiness
> that plagues /proc).  You can create a stat directory with a bunch of
> files, but not a single file that gives all values.
> 

The sysfs files in the patch export the statistics in the same way as the
disk statistics are exported (cf. linux/Documentation/iostats.txt). This
would enable the tools parson iostats easily analyze statistics also for
tapes.

The statistics represent the status at one time point and must be read
together (within reason). This means that splitting the values to several
files is not a proper way to export the information.

What then is the proper way? Debugfs?

Thanks,
Kai

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