Bug#1063753: systemd: IFB network devices are no longer autocreated when ifb module is loaded

[Andreas Sundstrom]

Package: systemd
Version: 252.22-1~deb12u1
Severity: important
X-Debbugs-Cc: sunkan+debian.bugs at zappa.cx

Dear Maintainer,

After upgrading systemd from 252.19-1~deb12u1 to 252.22-1~deb12u1
(Bookworm 12.4 to 12.5) the IFB network devices are no longer
automatically created when loading the `ifb` module. This is a
regression since previous releases as there is nothing mentioned about
this in the changelog.

It seems the root cause is that the following has been added to
/lib/modprobe.d/systemd.conf

[part of .../systemd.conf]
# Do the same for ifb0.

options ifb numifbs=0
[end]

How this will affect your system depends a lot on what you use the IFB
device(s) for. In my case it is used in combination with a QoS
scheduling/shaping setup.

For now I have worked around this change by adding the IFB device I
needed manually with the command `ip link add ifb0 numtxqueues 8 type
ifb`. And from what I can tell the kernel default setting is
`numifbs=2`.