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

[dann frazier]

And here's some proposed text. I assume this would be applicable to the
release notes from 20.04->22.04

= Known Issues =
== Network Interface Names ==
Ubuntu generates [predictable interface names](https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/) by default. These names are influenced by the information exposed by kernel drivers, and this can therefore vary from kernel release to kernel release. For example, Mellanox Connect-X 5 adapters are known to be assigned names such as enp1s0f0 with Linux 5.4, but be assigned a name like enp1s0f0np1 in Linux >= 5.8 (bug 1940860). If you find your system is impacted by such a name change after a kernel upgrade, you will need to update your network configuration files. If you would like to retain the same network interface names when switching between kernels, [netplan](https://netplan.io/reference/) provides a "set-name" field you can apply to your interface configuration. When set, this will cause Ubuntu to use the defined name instead of the default.

** Changed in: systemd (Ubuntu)
       Status: New => Invalid

** Changed in: linux (Ubuntu)
       Status: Confirmed => Won't Fix

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https://bugs.launchpad.net/bugs/1940860

Title:
  Mellanox NIC interface names change between 5.4 and 5.8

Status in subiquity:
  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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