Date:	Sat, 24 May 2008 00:16:30 -0500
From:	Matt Domsch <Matt_Domsch@...l.com>
To:	Jan Engelhardt <jengelh@...ozas.de>
Cc:	Jon Masters <jonathan@...masters.org>, Thomas Graf <tgraf@...g.ch>,
	Rick Jones <rick.jones2@...com>,
	"Kok, Auke" <auke-jan.h.kok@...el.com>, johnathan@...masters.org,
	netdev@...r.kernel.org, dwmw2@...radead.org
Subject: Re: network interface *name* alias support?

On Sat, May 24, 2008 at 06:53:17AM +0200, Jan Engelhardt wrote:
> 
> On Saturday 2008-05-24 06:25, Jon Masters wrote:
> >
> >I guess that would also work quite nicely for what I want to do, but the
> >problem is that this will require either:
> >
> >*). The kernel decodes the DMI extension directly.

which is pretty easy to do.

>*). We can first inform each device which slot it is in (set the slot).
> >
> >My intention is to implement whatever seems reasonable, and my reason
> >for asking is that I am not a networking maintainer, so I want to know
> >what seems reasonable :)
> 
> Why are we even looking at slot numbers? I do not think there is any
> guarantee that the order of slots as a human would recognize them on
> the board must always correspond to a monotonically increasing linear
> function.

The guarantee comes from the SMBIOS tables describing the slot
physically, including the label on the motherboard for it, as well as
the new SMBIOS table bits in the 2.6 spec that provide the linkage
between a PCI domain/bus/device/function to slot (or embedded)
mapping.  New type 41, and extended type 9, can provide this linkage.
Dell late-model servers implement this in their BIOS.

Just to throw a wrench in, look at how udev handles disks presently.
The same physical device is represented in at least 6 different ways:
/dev/disk/by-{id,label,path,uuid,edd} and /dev/sdX.  There was much
confusion at first when the /dev/hda IDE driver device names changed
to /dev/sda with the advent of libata.  People used these alternate
naming schemes to circumvent the problem.  The by-label and by-uuid
names didn't change.  Only the tools that hard-coded /dev/hda needed
to change.

Conceptually I'm looking for the same thing.  The kernel uses the
names ethN for most ethernet type devices.  However, there might be
logical names we would want to assign (public, private, dmz, ...), or
some form of BIOS-assigned (Gb1, Gb2 to match the label printed on the
chassis), or some form of physical placement names (eth_embedded1,
eth_embedded2, eth_slot1_1 and eth_slot1_2 for a multiport card),
etc.  Right now network devices have essentially one name; yes, you
can change it, at the peril of breaking all the tools that assume your
network cards are ethN, just as there was breakage for tools that
assumed disks were /dev/hda.  But you can't have the multiple names.

In Fedora 10 rawhide, I'm prepared to change the names of the network
devices from ethN to eth_s0_1 (first embedded NIC) very early in the
process and try to find what all breaks.  But it would be really nice
to be able to assign these other types of names to a device as well,
ideally without breaking tools that are counting on the ethN names.

Any options for doing so would be appreciated.

Thanks,
Matt


-- 
Matt Domsch
Linux Technology Strategist, Dell Office of the CTO
linux.dell.com & www.dell.com/linux
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