netdev - Re: use a special value of -2 for virtual devices to report indeterminate speed?

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Date:	Fri, 18 Nov 2011 19:13:19 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Rick Jones <rick.jones2@...com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Olaf Hering <olaf@...fle.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: use a special value of -2 for virtual devices to report
 indeterminate speed?

On Fri, 2011-11-18 at 10:58 -0800, Rick Jones wrote:
> On 11/18/2011 10:46 AM, Jeremy Fitzhardinge wrote:
> > On 11/18/2011 10:44 AM, Rick Jones wrote:
> >>   It could I suppose, decide
> >> based on the physical NIC to which it is attached, so long as folks
> >> using the virtual NIC don't expect its attributes to be the same from
> >> system to system.
> >
> > And assuming there's a physical NIC at all.
> 
> It sounds like we need a way to specify "Indeterminate" for link speed? 
>   Or some verbiage to that effect. Right now 0 and -1 cause ethtool to 
> report "Unknown!"
> 
>          if (speed == 0 || speed == (u16)(-1) || speed == (u32)(-1))
>                  fprintf(stdout, "Unknown!\n");
>          else
>                  fprintf(stdout, "%uMb/s\n", speed);
> 
> 
> How about -2 for the u32 cast value of speed returning "Indeterminate" 
> or something like that?  Not in "proper" patch format:
> 
> 	if (speed == 0 || speed == (u16)(-1) || speed == (u32)(-1))
> 		fprintf(stdout, "Unknown!\n");
> 	else if (speed == (u32)(-2))
> 		fprintf(stdout, "Indeterminate.");
> 	else
> 		fprintf(stdout, "%uMb/s\n", speed);

I'm open to something like this, but the problem with assigning new
magic numbers is that older versions of ethtool won't know to report
them as special.

We should also consider stacked drivers like bonding (and presumably
team) that expect real numbers when the link is up.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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