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

[Pali Rohár]

On Tuesday 09 August 2022 18:41:25 Sean Anderson wrote:
> 
> 
> On 8/9/22 5:42 PM, Pali Rohár wrote:
> > On Tuesday 09 August 2022 17:36:52 Sean Anderson wrote:
> >> 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 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?
> >> > 
> >> 
> >> 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
> > 
> > In linux:
> > $ git grep '"label"' net/dsa/dsa2.c
> > net/dsa/dsa2.c: const char *name = of_get_property(dn, "label", NULL);
> > 
> 
> Hm, if Linux is using the label, then do we need to rename things in userspace?

It uses it _only_ for DSA drivers. For all other drivers (e.g. USB or
PCIe based network adapters) it does not use label.