netdev - RE: [RFC PATCH] Initialize dev_id sysfs attribute to -1 by default

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Date:	Mon, 10 Jun 2013 11:11:45 -0700
From:	<Narendra_K@...l.com>
To:	<john.fastabend@...il.com>, <bhutchings@...arflare.com>
CC:	<john.r.fastabend@...el.com>, <bjorn@...k.no>,
	<netdev@...r.kernel.org>, <yoshfuji@...ux-ipv6.org>
Subject: RE: [RFC PATCH] Initialize dev_id sysfs attribute to -1 by default

> -----Original Message-----
> From: John Fastabend [mailto:john.fastabend@...il.com]
> Sent: Friday, June 07, 2013 10:45 PM
> To: Ben Hutchings
> Cc: John Fastabend; K, Narendra; bjorn@...k.no; netdev@...r.kernel.org;
> yoshfuji@...ux-ipv6.org
> Subject: Re: [RFC PATCH] Initialize dev_id sysfs attribute to -1 by default
> 

[...]
> >>
> >> Although I'm not sure how that check works with devices that are
> >> setting dev_id and also provide their own mac addresses. From
> >> inspection it looks like these devices end up with a local interface
> >> identifier unnecessarily.
> >>
> >> Maybe Ben knows one of the drivers is the siena solorflare controller
> >> apparently for the SFC9000 family? The other two 'grep' finds are an
> >> mlx and chelsio device.
> >>
> >> Interestingly I didn't find any devices setting dev_id that also
> >> didn't program unique mac addresses. Perhaps I'm missing something?
> >
> > I set this for Siena so that userland can tell which PF and port is
> > which even if the PCIe topology is hidden by virtualisation.  In
> > practice we haven't made use of that (and since virtualisation may
> > also hide the VPD and serial number capabilities, it probably doesn't
> > help much).
> >
> > Ben.
> >
> 
> I guess then to make dev_id work like Narendra wants you would need
> something in the management stack to come through and assign unique
> dev_id values to functions (net_devices) that share a MAC. Or have some
> unique 'unsigned short' value in the driver that it could be set to.
> I guess I miss why initializing it to -1 helps.
> 

Hi John, thank you for the inputs.  It was set to  -1 to differentiate between driver setting it to zero and the default value zero.

With regards,
Narendra K
Linux Engineering
Dell Inc.