ethernet<n> dt aliases implications in U-Boot and Linux

[Pali Rohár]

On Tuesday 09 August 2022 16:48:23 Sean Anderson wrote:
> On 8/8/22 5:45 PM, Michal Suchánek wrote:
> > On Mon, Aug 08, 2022 at 02:38:35PM -0700, Stephen Hemminger wrote:
> >> On Mon, 8 Aug 2022 23:09:45 +0200
> >> Michal Suchánek <msuchanek at suse.de> wrote:
> >> 
> >> > On Mon, Aug 08, 2022 at 03:57:55PM -0400, Sean Anderson wrote:
> >> > > Hi Tim,
> >> > > 
> >> > > On 8/8/22 3:18 PM, Tim Harvey wrote:  
> >> > > > Greetings,
> >> > > > 
> >> > > > I'm trying to understand if there is any implication of 'ethernet<n>'
> >> > > > aliases in Linux such as:
> >> > > >         aliases {
> >> > > >                 ethernet0 = &eqos;
> >> > > >                 ethernet1 = &fec;
> >> > > >                 ethernet2 = &lan1;
> >> > > >                 ethernet3 = &lan2;
> >> > > >                 ethernet4 = &lan3;
> >> > > >                 ethernet5 = &lan4;
> >> > > >                 ethernet6 = &lan5;
> >> > > >         };
> >> > > > 
> >> > > > I know U-Boot boards that use device-tree will use these aliases to
> >> > > > name the devices in U-Boot such that the device with alias 'ethernet0'
> >> > > > becomes eth0 and alias 'ethernet1' becomes eth1 but for Linux it
> >> > > > appears that the naming of network devices that are embedded (ie SoC)
> >> > > > vs enumerated (ie pci/usb) are always based on device registration
> >> > > > order which for static drivers depends on Makefile linking order and
> >> > > > has nothing to do with device-tree.
> >> > > > 
> >> > > > Is there currently any way to control network device naming in Linux
> >> > > > other than udev?  
> >> > > 
> >> > > You can also use systemd-networkd et al. (but that is the same kind of mechanism)
> >> > >   
> >> > > > Does Linux use the ethernet<n> aliases for anything at all?  
> >> > > 
> >> > > No :l  
> >> > 
> >> > Maybe it's a great opportunity for porting biosdevname to DT based
> >> > platforms ;-)
> >> 
> >> Sorry, biosdevname was wrong way to do things.
> >> Did you look at the internals, it was dumpster diving as root into BIOS.
> > 
> > When it's BIOS what defines the names then you have to read them from
> > the BIOS. Recently it was updated to use some sysfs file or whatver.
> > It's not like you would use any of that code with DT, anyway.
> > 
> >> Systemd-networkd does things in much more supportable manner using existing
> >> sysfs API's.
> > 
> > Which is a dumpster of systemd code, no thanks.
> > 
> > I want my device naming independent of the init system, especially if
> > it's systemd.
> 
> Well, there's always nameif...
> 
> That said, I have made [1] for people using systemd-networkd.
> 
> --Sean
> 
> [1] https://github.com/systemd/systemd/pull/24265

Hello!

In some cases "label" DT property can be used also as interface name.
For example this property is already used by DSA kernel driver.

I created very simple script which renames all interfaces in system to
their "label" DT property (if there is any defined).

#!/bin/sh
for iface in `ls /sys/class/net/`; do
	for of_node in of_node device/of_node; do
		if test -e /sys/class/net/$iface/$of_node/; then
			label=`cat /sys/class/net/$iface/$of_node/label 2>/dev/null`
			if test -n "$label" && test "$label" != "$iface"; then
				echo "Renaming net interface $iface to $label..."
				up=$((`cat /sys/class/net/$iface/flags 2>/dev/null || echo 1` & 0x1))
				if test "$up" != "0"; then
					ip link set dev $iface down
				fi
				ip link set dev $iface name "$label" && iface=$label
				if test "$up" != "0"; then
					ip link set dev $iface up
				fi
			fi
			break
		fi
	done
done

Maybe it would be better first to use "label" and then use ethernet alias?