[Bug 1940860] Re: Mellanox NIC interface names change between 5.4 and 5.8

[Javier Diaz Jr]

This also affects the ubuntu-installer when the `d-i base-
installer/kernel/override-image          string linux-generic-hwe-20.04`
flag is added to preseed. The installer loads 5.4 kernel and configure
NICs using the 5.4 naming convention, then once the 5.11 kernel is
loaded and the host reboots the network config fails.

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Title:
  Mellanox NIC interface names change between 5.4 and 5.8

Status in subiquity:
  New
Status in Release Notes for Ubuntu:
  New
Status in linux package in Ubuntu:
  Won't Fix
Status in systemd package in Ubuntu:
  Invalid

Bug description:
  I noticed on a couple of systems that my network interface names
  change when upgrading from the focal LTS (5.4) kernel to the focal HWE
  (both 5.8 & 5.11) kernels. Both systems have Mellanox Connect-X 5
  NICs.

  dannf at bizzy:~$ uname -a
  Linux bizzy 5.4.0-81-generic #91-Ubuntu SMP Thu Jul 15 19:10:30 UTC 2021 aarch64 aarch64 aarch64 GNU/Linux
  dannf at bizzy:~$ ls /sys/class/net
  enp1s0f0  enp1s0f1  enx3e8734bc294f  lo

  dannf at bizzy:~$ uname -a
  Linux bizzy 5.8.0-63-generic #71~20.04.1-Ubuntu SMP Thu Jul 15 17:46:44 UTC 2021 aarch64 aarch64 aarch64 GNU/Linux
  dannf at bizzy:~$ ls /sys/class/net
  enp1s0f0np0  enp1s0f1np1  enx3e8734bc294f  lo

  dannf at bizzy:~$ uname -a
  Linux bizzy 5.11.0-27-generic #29~20.04.1-Ubuntu SMP Wed Aug 11 15:58:08 UTC 2021 aarch64 aarch64 aarch64 GNU/Linux
  dannf at bizzy:~$ ls /sys/class/net
  enp1s0f0np0  enp1s0f1np1  enx3e8734bc294f  lo

  I bisected this down to a kernel change:
  # first bad commit: [c6acd629eec754a9679f922d51f90e44c769b80c] net/mlx5e: Add support for devlink-port in non-representors mode

  The impact is that your network can fail to come up after
  transitioning from the LTS kernel to the HWE kernel. Now, this isn't a
  huge problem for MAAS installs because MAAS configures netplan to
  always use the same names as were used at commissioning. It does
  impact subiquity based installs however, which do not.

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