Re: [PATCH] wireless: sysfs was displaying different values for level and noise than procfs

["John W. Linville" <linville@tuxdriver.com>]

On Wed, Nov 19, 2008 at 10:45:21PM +0300, Andrey Borzenkov wrote:
> On Wednesday 19 November 2008, Pavel Roskin wrote:
> > On Sat, 2008-11-15 at 18:31 +0300, Andrey Borzenkov wrote:
> > > Subject: [PATCH] wireless: sysfs was displaying different values for level and noise than procfs
> > > From: Andrey Borzenkov <arvidjaar@mail.ru>
> > > 
> > > /proc/net/wireless asjusts display of signal and noise level depending on
> > > whether units are percentage or dBm. Use the same format in sysfs. This
> > > makes it easy to know unit - below zero is dBm, above zero is percent.
> > 
> > I've seen received power up to 3 dBm.  The AP was using an amplifier
> > (it's specialized hardware), and it's possible that the card on the
> > station side was exaggerating the signal.  However, the data we report
> > should not need any guesswork to be interpreted.  It may be parsed by
> > userspace software.
> > 
> 
> But positive dBm is not even possible to represnt right now. It is u8 and
> is displayed as ((s32)level - 256); so it is *always* negative.
> 
> > Receiving 1 mW out of 200 mW is not impossible in some antenna
> > configurations even with consumer devices.
> > 
> > > Before:
> > > {pts/1}% cat /sys/class/net/eth1/wireless/level
> > > 203
> > > {pts/1}% cat /sys/class/net/eth1/wireless/noise
> > > 166
> > 
> > > +	return sprintf(buf, format_string, (__s32)iw->field -		\
> > > +			((iw->qual.updated & IW_QUAL_DBM) ? 0x100 : 0)); \
> > 
> > I think non-dBm data should be shown in a special format: "203/255"
> > where 255 is the maximal value, and the dBm data should be shown as
> > numbers: "-48".  This way, we encourage use of dBm data by making it
> > easier to parse.
> > 
> 
> Well, I do not have any strong opinion regarding this; I just noticed
> discrepancy between procfs and sysfs for what effectively is the same raw
> value.

And what is your perspective regarding potential 'userland ABI'
issues of either this patch or of Pavel's suggestion?

John
-- 
John W. Linville		Linux should be at the core
linville@tuxdriver.com			of your literate lifestyle.