netdev - Re: [PATCH] udev: create empty regular files to represent net interfaces

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Message-Id: <1256834975.2827.63.camel@achroite>
Date:	Thu, 29 Oct 2009 16:49:35 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Greg KH <greg@...ah.com>
Cc:	Matt Domsch <Matt_Domsch@...l.com>,
	Kay Sievers <kay.sievers@...y.org>,
	dann frazier <dannf@...com>, linux-hotplug@...r.kernel.org,
	Narendra_K@...l.com, netdev@...r.kernel.org,
	Jordan_Hargrave@...l.com, Charles_Rose@...l.com
Subject: Re: [PATCH] udev: create empty regular files to represent net
	interfaces

On Thu, 2009-10-29 at 07:25 -0700, Greg KH wrote:
> On Thu, Oct 29, 2009 at 08:11:25AM -0500, Matt Domsch wrote:
> > Netdev team - are you in agreement that having multiple names to
> > address the same netdevice is a worthwhile thing to add, to allow a
> > variety of naming schemes to exist simultaneously?  If not, this whole
> > discussion will be moot, and my basic problem, that the ethX naming
> > convention is nondeterministic, but we need determinism, remains
> > unresolved.
> 
> I'm still totally confused as to why you think this.  What is wrong with
> what we do today, which is name network devices in a deterministic
> manner by their MAC in userspace?  That name goes into the kernel, and
> everyone uses the same name and is happy.
> 
> If you don't like naming by MAC, then pick some other deterministic
> naming scheme that works for your hardware and write udev rules for it.
> 
> You could easily name them in a way that could keep the lowest number
> (eth0) for the lowest PCI id if you so desired and your BIOS guaranteed
> it.
> 
> This way the kernel has only one name, and so does userspace, and
> everyone is happy.

I thought there was a general trend in udev development to provide
default rules that work for almost everyone, so few users/administrators
need to override or add to them.  Compare disks and net devices:

1. Stable kernel device id
Disks: block device number
Net devices: ifindex

2. Unique identifier (across reboot)
Disks: label or UUID (each with limitations)
Net devices: (MAC address, subtype)

3. Name assignment mechanism
Disks: kernel suggests a name; udev can assign any number
Net devices: kernel assigns a single name; udev can override it

4. Default name assignment policy
Disks: names disk by device path (id), label and UUID
Net devices: assigns arbitrary stable names per (MAC address, subtype)

5. Naming by users
Disks: user can identify by any method without having to choose on a
system-wide basis
Net devices: user must identify by single name; policy can be overridden
on a system-wide basis

I fully understand the technical reasons for differences 3-5, but why
should users have to put up with it?

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
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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