[Bug 1884281] Re: UC20 images do not use predictable interface names on RPi4

Thu Jun 25 12:22:23 UTC 2020

The default for both core20 and server is 'net.ifnames=0' which disables
persistent network interface names so it's expected to see eth0 and
wlan0.

cat /proc/cmdline 
 coherent_pool=1M 8250.nr_uarts=1 bcm2708_fb.fbwidth=1280 bcm2708_fb.fbheight=1024 bcm2708_fb.fbswap=1 smsc95xx.macaddr=DC:A6:32:08:85:96 vc_mem.mem_base=0x3ec00000 vc_mem.mem_size=0x40000000  net.ifnames=0 dwc_otg.lpm_enable=0 root=LABEL=writable rootfstype=ext4 elevator=deadline rootwait fixrtc console=tty1 console=ttyS0,115200 quiet splash

However, if I drop 'net.ifnames=0' from cmdline.txt I *do* get a
persistent name on a 3B+ but *not* on a 4B.

On a Pi 3B:

$ udevadm info /sys/class/net/enxb827eb3eabfb 
P: /devices/platform/soc/3f980000.usb/usb1/1-1/1-1.1/1-1.1.1/1-1.1.1:1.0/net/enxb827eb3eabfb
L: 0
E: DEVPATH=/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.1/1-1.1.1/1-1.1.1:1.0/net/enxb827eb3eabfb
E: INTERFACE=enxb827eb3eabfb
E: IFINDEX=2
E: SUBSYSTEM=net
E: USEC_INITIALIZED=5428547
E: ID_MM_CANDIDATE=1
E: ID_NET_NAMING_SCHEME=v245
E: ID_NET_NAME_MAC=enxb827eb3eabfb
E: ID_OUI_FROM_DATABASE=Raspberry Pi Foundation
E: ID_VENDOR=0424
E: ID_VENDOR_ENC=0424
E: ID_VENDOR_ID=0424
E: ID_MODEL=7800
E: ID_MODEL_ENC=7800
E: ID_MODEL_ID=7800
E: ID_REVISION=0300
E: ID_SERIAL=0424_7800
E: ID_TYPE=generic
E: ID_BUS=usb
E: ID_USB_INTERFACES=:ff00ff:
E: ID_USB_INTERFACE_NUM=00
E: ID_USB_DRIVER=lan78xx
E: ID_USB_CLASS_FROM_DATABASE=Vendor Specific Class
E: ID_VENDOR_FROM_DATABASE=Microchip Technology, Inc. (formerly SMSC)
E: ID_PATH=platform-3f980000.usb-usb-0:1.1.1:1.0
E: ID_PATH_TAG=platform-3f980000_usb-usb-0_1_1_1_1_0
E: ID_NET_DRIVER=lan78xx
E: ID_NET_LINK_FILE=/usr/lib/systemd/network/73-usb-net-by-mac.link
E: ID_NET_NAME=enxb827eb3eabfb
E: SYSTEMD_ALIAS=/sys/subsystem/net/devices/enxb827eb3eabfb
E: TAGS=:systemd:

$  udevadm test-builtin net_id /sys/class/net/enxb827eb3eabfb 
Load module index
Parsed configuration file /usr/lib/systemd/network/99-default.link
Parsed configuration file /usr/lib/systemd/network/73-usb-net-by-mac.link
Created link configuration context.
Using default interface naming scheme 'v245'.
ID_NET_NAMING_SCHEME=v245
ID_NET_NAME_MAC=enxb827eb3eabfb
ID_OUI_FROM_DATABASE=Raspberry Pi Foundation
Unload module index
Unloaded link configuration context.

/usr/lib/systemd/network/73-usb-net-by-mac.link is the systemd policy
file that handles the renaming of eth0.

On a Pi 4B:

$ udevadm info /sys/class/net/eth0 
P: /devices/platform/scb/fd580000.ethernet/net/eth0
L: 0
E: DEVPATH=/devices/platform/scb/fd580000.ethernet/net/eth0
E: INTERFACE=eth0
E: IFINDEX=2
E: SUBSYSTEM=net
E: USEC_INITIALIZED=2348632
E: ID_MM_CANDIDATE=1
E: ID_NET_NAMING_SCHEME=v245
E: ID_NET_NAME_MAC=enxdca632088596
E: ID_OUI_FROM_DATABASE=Raspberry Pi Trading Ltd
E: ID_PATH=platform-fd580000.ethernet
E: ID_PATH_TAG=platform-fd580000_ethernet
E: ID_NET_DRIVER=bcmgenet
E: ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link
E: SYSTEMD_ALIAS=/sys/subsystem/net/devices/eth0
E: TAGS=:systemd:

$ udevadm test-builtin net_id /sys/class/net/eth0 
Load module index
Parsed configuration file /usr/lib/systemd/network/99-default.link
Parsed configuration file /usr/lib/systemd/network/73-usb-net-by-mac.link
Created link configuration context.
Using default interface naming scheme 'v245'.
ID_NET_NAMING_SCHEME=v245
ID_NET_NAME_MAC=enxdca632088596
ID_OUI_FROM_DATABASE=Raspberry Pi Trading Ltd
Unload module index
Unloaded link configuration context.

systemd can't handle the platform attached bcmgenet driver of the Pi 4B
so hence no renaming.

I've created the following systemd file

$ cat /etc/systemd/network/73-platform-net-by-mac.link 
[Match]
Path=platform-*.ethernet

[Link]
NamePolicy=mac

rebooted and ended up with a persistent net name for eth0:

$ udevadm info /sys/class/net/enxdca632088596
P: /devices/platform/scb/fd580000.ethernet/net/enxdca632088596
L: 0
E: DEVPATH=/devices/platform/scb/fd580000.ethernet/net/enxdca632088596
E: INTERFACE=enxdca632088596
E: IFINDEX=2
E: SUBSYSTEM=net
E: USEC_INITIALIZED=2337681
E: ID_MM_CANDIDATE=1
E: ID_NET_NAMING_SCHEME=v245
E: ID_NET_NAME_MAC=enxdca632088596
E: ID_OUI_FROM_DATABASE=Raspberry Pi Trading Ltd
E: ID_PATH=platform-fd580000.ethernet
E: ID_PATH_TAG=platform-fd580000_ethernet
E: ID_NET_DRIVER=bcmgenet
E: ID_NET_LINK_FILE=/etc/systemd/network/73-platform-net-by-mac.link
E: ID_NET_NAME=enxdca632088596
E: SYSTEMD_ALIAS=/sys/subsystem/net/devices/enxdca632088596 /sys/subsystem/net/devices/enxdca632088596
E: TAGS=:systemd:

Don't know if that's the right way to do this. Also, wlan0 still has a non-persistent name, so that needs to be addressed too if we want to go that route.

** Changed in: linux-raspi (Ubuntu)
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/1884281

Title:
  UC20 images do not use predictable interface names on RPi4

Status in snapd:
  Triaged
Status in linux-raspi package in Ubuntu:
  Invalid
Status in systemd package in Ubuntu:
  New

Bug description:
  Image tested: http://cdimage.ubuntu.com/ubuntu-core/20/dangerous-
  beta/pending/ubuntu-core-20-arm64+raspi.img.xz

  Boot the image and check the naming of the ethernet interfaces. On
  most devices (amd64, rpi3 etc) systemd predicatable interface naming
  is applied e.g. enxb827eb7d1eee. However on specifically RPi4 devices
  traditional naming is used e.g. eth0, eth1.

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