Hello,
I've been trying to figure out how predictable interface naming works,
especially the "on-board index number", that the firmware apparently
passes(?)
I'm currently working on a port for the ASRock B75M-ITX, which has a
Realtek NIC as PCI device 03:00.0. The Linux kernel calls this device
enp3s0, which makes sense and works fine. However, on my ASUS P8Z77-V
and my Lenovo X230, the Intel NIC is called eno0, which makes more
sense, because it's "ethernet onboard 0" and not a physical network card
stuck in a PCI Express slot.
At first I thought that maybe this was an e1000e-specific way of naming
interfaces, but at the office I have an old Gigabyte GA-G41M-ES2L-based
file server, running coreboot, also with a Realtek NIC, also being PCI
device 03:00.0, which is called eno0 by the kernel as well, with enp3s0
as altname. (So it's not that.)
I ended up reading about the interface (re)naming process, which seems
to be handled by systemd-udevd [1]:
---
The following different naming schemes for network interfaces are now
supported by udev natively:
1. Names incorporating Firmware/BIOS provided index numbers for on-board
devices (example: eno1)
2. Names incorporating Firmware/BIOS provided PCI Express hotplug slot
index numbers (example: ens1)
3. Names incorporating physical/geographical location of the connector
of the hardware (example: enp2s0)
4. Names incorporating the interfaces's MAC address (example:
enx78e7d1ea46da)
5. Classic, unpredictable kernel-native ethX naming (example: eth0)
---
It looks like my B75M-ITX currently uses option 3, while I want it to
use option 1, like all my other machines do. So according to the
documentation, interfaces called enoX or ensX use index numbers provided
by the firmware. However, I have no idea how or where this is defined. I
would expect something to be in devicetree.cb, but I can't see anything
seemingly related anywhere.
So my question is: how does coreboot pass "index numbers for on-board
devices" to the kernel / udev, and how can I define them properly on
boards where this is not working the way it should?
[1] https://systemd.io/PREDICTABLE_INTERFACE_NAMES/
--
With kind regards,
Kevin Keijzer
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