Re: How to document dimension units for virtual files?

[Michael Holzheu <HOLZHEU@de.ibm.com>]

Hi Ingo,

Ingo Oeser <ioe-lkml@rameria.de> wrote on 10/23/2006 09:03:32 PM:

[snip]

> > 2. Encode dimension unit into filename (e.g. onlinetime_ms or
memory_kb)
>
> This is the recommended one.
> - simple to implement and understand on both sides
>
> - if you change units, you notice breaking userspace immediately
>   and can even notice it being used in closed source tools
>   with a simple strace
>
> - no parsing involved, as the author of the user space tool
>   usually assumes the unit implicitly (like "programming by contract",
where
>   the "contract" is the filename, which is quite easy to check for.
>
> - you can keep a legacy interface with neglible effort and code wastage
>
> - many advantages I forgot :-)
>

I also think that this is the best solution. It would be nice to have
that documented somewhere. Maybe in the Documentation directory
something like:

Howto export data in virtual files
==================================

If you want to export data to userspace via virtual filesystems
like procfs, sysfs, debugfs etc., the following rules are recommended:

- Export only one value in one virtual file.
- Data format should be as simple as possible.
- Use ASCII formated strings, no binary data if possible.
- If data has dimension units, encode that in the filename.
  Please use the following suffixes:
  * kb: Kilobytes
  * mb: Megabytes
  * ms: Milliseconds
  * us: Microseconds
  * ns: Nanoseconds
  * ...

Examples:
---------
> ls /sys/mydata
memory_kb
online_time_ms

> cat /sys/mydata/memory_kb
4769

Michael

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