-----Original Message-----
From: Kai Mäkisara [mailto:kai.makis...@kolumbus.fi] 
Sent: Wednesday, February 27, 2013 4:38 AM
To: James Bottomley
Cc: Seymour, Shane M; linux-scsi@vger.kernel.org
Subject: Re: [Patch][RFC] st: provide tape statistics via sysfs


> 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.

Can I make a counter proposal that doesn't introduce any more ABI compatibility 
issues than already exist in sysfs? I'll create a statistics directory as James 
suggested and expose all of the individual statistics in their own files one 
value per file. I'll remove the extra field I wanted to add from the stat file 
and make it identical to the file provided for disk statistics and move the 
file down into the statistics directory under the device (with a warning in the 
code that this file must provide exactly the same information as the disks stat 
file and cannot provide more than that). To get the statistics I want to get 
I'll use the stat file plus one of the individual files. I'd still like to keep 
the file with the hint about how many tape drives there will be as a maximum.

> 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.

One file would be better than two, but two is a lot better than having to open 
and read all of them individually and get stats that really are an 
approximation. 
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