Date: Wed, 8 Nov 2006 09:04:54 -0800
From: Randy Dunlap <randy.dunlap@oracle.com>
To: Michael Holzheu <holzheu@de.ibm.com>
Cc: pavel@ucw.cz, Ingo Oeser <ioe-lkml@rameria.de>,
       linux-kernel@vger.kernel.org, mschwid2@de.ibm.com
Subject: Re: How to document dimension units for virtual files?
Message-Id: <20061108090454.dba20e01.randy.dunlap@oracle.com>
In-Reply-To: <20061108175412.3c2be30c.holzheu@de.ibm.com>
References: <20061108175412.3c2be30c.holzheu@de.ibm.com>
Organization: Oracle Linux Eng.
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On Wed, 8 Nov 2006 17:54:12 +0100 Michael Holzheu wrote:

> Pavel, Ingo,
> 
> Pavel Machek <pavel@ucw.cz> wrote on 10/28/2006 07:40:48 PM:
> > Hi!
> > 
> > > > > 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
> > > >
> 
> [snip]
> 
> > > 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:
> > 
> > ...yes please... such patch would be nice.
> 
> What about the following ...
> 
> Michael
> 
> ---
> 
>  Documentation/filesystems/00-INDEX   |    2 +
>  Documentation/filesystems/ExportData |   47 +++++++++++++++++++++++++++++++++++
>  2 files changed, 49 insertions(+)
> 
> diff -Naur linux-2.6.18/Documentation/filesystems/00-INDEX linux-2.6.18-exp-data-doc/Documentation/filesystems/00-INDEX
> --- linux-2.6.18/Documentation/filesystems/00-INDEX	2006-09-20 10:50:34.000000000 +0200
> +++ linux-2.6.18-exp-data-doc/Documentation/filesystems/00-INDEX	2006-11-08 17:45:31.000000000 +0100
> @@ -1,5 +1,7 @@
>  00-INDEX
>  	- this file (info on some of the filesystems supported by linux).
> +ExportData
> +	- recommendation of how to export data via virtual File Systems.
>  Exporting
>  	- explanation of how to make filesystems exportable.
>  Locking
> diff -Naur linux-2.6.18/Documentation/filesystems/ExportData linux-2.6.18-exp-data-doc/Documentation/filesystems/ExportData
> --- linux-2.6.18/Documentation/filesystems/ExportData	1970-01-01 01:00:00.000000000 +0100
> +++ linux-2.6.18-exp-data-doc/Documentation/filesystems/ExportData	2006-11-08 17:44:59.000000000 +0100
> @@ -0,0 +1,47 @@
> +
> +Export data via virtual File Systems
> +====================================
> +
> +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.

I don't think that makes sense for procfs.  It's too late,
but even it weren't, we don't need a large increase in the number
of procfs files.

And debugfs shouldn't be constrained either.
It's not a regular user interface like sysfs is.

> +- Data format should be as simple as possible.
> +- Use ASCII formated strings, no binary data if possible.

*              formatted

> +- If data has dimension units, encode that in the filename.
> +
> +Please use the following prefixes, when dimension units are required (According
> +to IEC 60027-2 and SI/International System of Units):
> +
> +Storage size (SI prefixes)
> +--------------------------
> +* kB: kilobyte (10^3 Byte)
> +* MB: megabyte (10^6 Byte)
> +* GB: gigabyte (10^9 Byte)
> +* TB: terabyte (10^12 Byte)
> +* PB: petabyte (10^15 Byte)
> +
> +Storage size (Binary prefixes)
> +------------------------------
> +* KiB: kibibyte (2^10 Byte)
> +* MiB: mebibyte (2^20 Byte)
> +* GiB: gibibyte (2^30 Byte)
> +* TiB: tebibyte (2^40 Byte)
> +* PiB: pebibyte (2^50 Byte)
> +
> +Time (SI pefixes)
> +-----------------
> +* s:  Second
> +* ms: Millisecond (10^-3 Seconds)
> +* us: Microsecond (10^-6 Seconds)
> +* ns: Nanosecond (10^-9 Seconds)
> +
> +Examples:
> +---------
> +> ls /sys/kernel/debug/sysinfo
> +free_mem_KiB
> +online_time_ms
> +cpu_time_us
> +
> +> cat /sys/kernel/debug/free_mem_KiB
> +147536
> -

---
~Randy
-
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