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

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Message-ID: <b1b33912-8898-f42d-5f30-0ca050fccf9a@seco.com>
Date:   Tue, 9 Aug 2022 17:36:52 -0400
From:   Sean Anderson <sean.anderson@...o.com>
To:     Pali Rohár <pali@...nel.org>
Cc:     Michal Suchánek <msuchanek@...e.de>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Tim Harvey <tharvey@...eworks.com>,
        netdev <netdev@...r.kernel.org>, u-boot <u-boot@...ts.denx.de>,
        Device Tree Mailing List <devicetree@...r.kernel.org>
Subject: Re: ethernet<n> dt aliases implications in U-Boot and Linux



On 8/9/22 5:31 PM, Pali Rohár wrote:
> 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@...e.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?
> 

It looks like there is already precedent for using ID_NET_LABEL_ONBOARD for
this purpose (on SMBios boards). It should be a fairly simple extension to
add that as well. However, I didn't find any uses of this in Linux or U-Boot
(although I did find plenty of ethernet LEDs). Do you have an example you
could point me to?

--Sean