Bug#953019: udev: unexpected network interface name changes on upgrade from stretch

[Sergio Gelato]

Package: udev
Version: 241-7~deb10u3

After upgrading a system from stretch to buster, the names of some network
interfaces changed unexpectedly. Specifically:

stretch# udevadm test-builtin net_id /sys/class/net/enp94s0f0
calling: test-builtin
=== trie on-disk ===
tool version:          232
file size:         8669279 bytes
header size             80 bytes
strings            1850783 bytes
nodes              6818416 bytes
Load module index
Found container virtualization none
timestamp of '/etc/systemd/network' changed
timestamp of '/lib/systemd/network' changed
Parsed configuration file /lib/systemd/network/99-default.link
Created link configuration context.
ID_NET_NAME_MAC=enxd09466xxxxxx
ID_NET_NAME_PATH=enp94s0f0
Unload module index
Unloaded link configuration context.

buster# udevadm test-builtin net_id /sys/class/net/ens1f0np0 
Load module index
Parsed configuration file /lib/systemd/network/99-default.link
Created link configuration context.
Using default interface naming scheme 'v240'.
ID_NET_NAMING_SCHEME=v240
ID_NET_NAME_MAC=enxd09466xxxxxx
ID_OUI_FROM_DATABASE=Dell Inc.
ID_NET_NAME_PATH=enp94s0f0np0
ID_NET_NAME_SLOT=ens1f0np0
Unload module index
Unloaded link configuration context.

This is the same interface, as shown by the ID_NET_NAME_PATH values.
Even if it weren't for the newly detected ID_NET_NAME_SLOT I think I would
still have had to reconfigure things due to the extra np# suffix.

I had serial console access so this was only a minor inconvenience, but
how could I have avoided being surprised? Isn't predictability the main
selling point for this interface naming scheme?

Some hardware info:

5e:00.0 Ethernet controller [0200]: Broadcom Limited BCM57416 NetXtreme-E 10GBase-T RDMA Ethernet Controller [14e4:16d8] (rev 01)

Handle 0x0901, DMI type 9, 17 bytes
System Slot Information
        Designation: Mezzanine 1
        Type: x8 PCI Express 3
        Current Usage: In Use
        Length: Other
        ID: 1
        Characteristics:
                3.3 V is provided
                PME signal is supported
        Bus Address: 0000:5e:00.0
Handle 0x0000, DMI type 0, 26 bytes
BIOS Information
        Vendor: Dell Inc.
        Version: 2.4.8
        Release Date: 11/27/2019
	[...]
Handle 0x0100, DMI type 1, 27 bytes
System Information
        Manufacturer: Dell Inc.
        Product Name: PowerEdge R440
	[...]