Public bug reported:
[Impact]
udev can produce unpredictable network interface names by default when multiple
devices map to the same slot due to an intermediate bridge. On an Nvidia DGX2
system, I see the following when booting a system with udev 245.4-4ubuntu3.13:
ubuntu@akis:~$ ls /sys/class/net
enp134s0f0 enp6s0 ens103 ens107 eth3 eth9
enp134s0f1 ens102 ens106 eth1 eth7 lo
For each ens* device, there is a sibling eth* device that maps to the
same slot because both devices are behind the same bridge.
Unpredictable names present well known problems, but I'll describe a
specific issue I'm having. We currently do automated network testing
that MAAS deploys a system and then configures 2 specific NICs on the
system. While MAAS does take care to always restore the names used
during commissioning (eth3 will always be the same NIC on every deploy),
these names can change each time the system is commissioned. So today we
need to go in and edit the NIC names manually in MAAS any time the
system is re-commissioned.
[Fix]
This issue was addressed upstream by adding a new v247 naming scheme that
detects this scenario and disables usage of slot-based names for these devices.
Obviously changing the default naming scheme in a released LTS series could
break users. However, we could introduce the v247 scheme in a focal SRU, and
keep the default scheme of v245 (via -Ddefault-net-naming-scheme=v245). Users
impacted by this could then opt-in to the v247 scheme by passing
net.naming-scheme=v247 or net.naming-scheme=latest on the kernel command line.
I could add this to DGX2 systems via a kernel_opts MAAS tag to always get
predictable names during commissioning.
[Regression Risk]
This would change the behavior of any users who select
net.naming-scheme=latest. I'm not sure why an existing Ubuntu user would be
doing that though - AFAICT, Ubuntu currently always defaults to the latest
scheme.
** Affects: systemd (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1945225
Title:
udev produces unpredictable net names when PCI device is a bridge
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