netdev - Re: PATCH: Network Device Naming mechanism and policy

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Date:	Sat, 10 Oct 2009 14:11:24 -0400
From:	Bill Fink <billfink@...dspring.com>
To:	Greg KH <greg@...ah.com>
Cc:	Matt Domsch <Matt_Domsch@...l.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	netdev@...r.kernel.org, linux-hotplug@...r.kernel.org,
	Narendra_K@...l.com, jordan_hargrave@...l.com
Subject: Re: PATCH: Network Device Naming mechanism and policy

On Fri, 9 Oct 2009, Greg KH wrote:

> On Fri, Oct 09, 2009 at 11:40:57PM -0500, Matt Domsch wrote:
> > The fundamental roadblock to this is that enumeration != naming,
> > except that it is for network devices, and we keep changing the
> > enumeration order.
> 
> No, the hardware changes the enumeration order, it places _no_
> guarantees on what order stuff will be found in.  So this is not the
> kernel changing, just to be clear.
> 
> Again, I have a machine here that likes to reorder PCI devices every 4th
> or so boot times, and that's fine according to the PCI spec.  Yeah, it's
> a crappy BIOS, but the manufacturer rightly pointed out that it is not
> in violation of anything.
> 
> > Today, port naming is completely nondeterministic.  If you have but
> > one NIC, there are few chances to get the name wrong (it'll be eth0).
> > If you have >1 NIC, chances increase to get it wrong.
> 
> That is why all distros name network devices based on the only
> deterministic thing they have today, the MAC address.  I still fail to
> see why you do not like this solution, it is honestly the only way to
> properly name network devices in a sane manner.
> 
> All distros also provide a way to easily rename the network devices, to
> place a specific name on a specific MAC address, so again, this should
> all be solved already.
> 
> No matter how badly your BIOS teams mess up the PCI enumeration order :)

No comment on the specific implementation decision, but I am in the
process of setting up a large number of test systems with identical
hardware configurations, and using a master disk image to clone all the
test systems.  The biggest pain in this process is identiying the MAC
addresses for each of the six or more network interfaces in each test
system (we want eth0...ethN to always reference the same physical port
on the test systems), and then having to modify the 70-persistent-net.rules
udev file and the HWADDR entry for all the ifcfg-ethX files to reflect
the correct MAC addresses.  It would be fantastic if there were some
mechanism for making this part of the process unnecessary.

						-Bill
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