Re: [docs] [PATCH] migration-guides/migration-5.3.rst: add note on systemd pni-names change

["Antonin Godard" <antonin.godard@bootlin.com>]

On Wed Sep 10, 2025 at 4:08 PM CEST, Quentin Schulz wrote:
> Hi Antonin,
>
> On 9/10/25 3:32 PM, Antonin Godard via lists.yoctoproject.org wrote:
>> On Wed Sep 10, 2025 at 3:16 PM CEST, Quentin Schulz via lists.yoctoproject.org wrote:
>>> Hi Antonin,
>>>
>>> On 9/10/25 3:08 PM, Antonin Godard wrote:
>>>> On Tue Sep 9, 2025 at 3:59 PM CEST, Quentin Schulz via lists.yoctoproject.org wrote:
>>>>> Hi Antonin,
>>>>>
>>>>> On 9/9/25 3:29 PM, Antonin Godard via lists.yoctoproject.org wrote:
>>>>>> Add a migration note on the pni-names default policy change after commit
>>>>>> <> in OE-Core.
>>>>>>
>>>>>
>>>>> General question, the systemd manpage specifies the policy as mac and
>>>>> not MAC, should we follow that as well?
>>>>>
>>>>>> Cc: Koen Kooi <koen.kooi@oss.qualcomm.com>
>>>>>> Cc: Ross Burton <Ross.Burton@arm.com>
>>>>>> Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
>>>>>> ---
>>>>>>     documentation/migration-guides/migration-5.3.rst | 25 ++++++++++++++++++++++++
>>>>>>     1 file changed, 25 insertions(+)
>>>>>>
>>>>>> diff --git a/documentation/migration-guides/migration-5.3.rst b/documentation/migration-guides/migration-5.3.rst
>>>>>> index 2d2f8d91a..8aa7b537f 100644
>>>>>> --- a/documentation/migration-guides/migration-5.3.rst
>>>>>> +++ b/documentation/migration-guides/migration-5.3.rst
>>>>>> @@ -118,6 +118,31 @@ class. Instead, one should create a new recipe to build this FIT image, as
>>>>>>     described in the :ref:`Removed Classes <migration-guides/migration-5.3:Removed
>>>>>>     Classes>` section of the Migration notes for |yocto-ver| (|yocto-codename|).
>>>>>>     
>>>>>> +systemd Predictable Interface Names no longer MAC policy by default
>>>>>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>> +
>>>>>> +The :oe_git:`systemd recipe </openembedded-core/tree/meta/recipes-core/systemd>`
>>>>>> +used to forcibly set the MAC policy by default when the ``pni-names``
>>>>>> +:term:`distro feature <DISTRO_FEATURES>` was enabled. See
>>>>>
>>>>> s/was/is/ ?
>>>>>
>>>>>> +https://www.freedesktop.org/software/systemd/man/latest/systemd.link.html#AlternativeNamesPolicy=.
>>>>>> +
>>>>>> +This is no longer the case. Instead, when the ``pni-names`` :term:`distro
>>>>>
>>>>> SHould we justify here why it is no longer the case?
>>>>>
>>>>>> +feature <DISTRO_FEATURES>` is enabled, the default policy from systemd is
>>>>>> +selected (from https://github.com/systemd/systemd/blob/main/network/99-default.link).
>>>>>> +
>>>>>> +To set the MAC policy to systemd, add the following to a systemd ``.bbappend``
>>>>>
>>>>> s/to systemd/in systemd/ ?
>>>>>
>>>>>> +file in your custom layer::
>>>>>> +
>>>>>> +   do_install:append() {
>>>>>> +          if ${@bb.utils.contains('PACKAGECONFIG', 'pni-names', 'true', 'false', d)}; then
>>>>>> +                  if ! grep -q '^NamePolicy=.*mac' ${D}${nonarch_libdir}/systemd/network/99-default.link; then
>>>>>> +                          sed -i '/^NamePolicy=/s/$/ mac/' ${D}${nonarch_libdir}/systemd/network/99-default.link
>>>>>> +                  fi
>>>>>> +                  if ! grep -q 'AlternativeNamesPolicy=.*mac' ${D}${nonarch_libdir}/systemd/network/99-default.link; then
>>>>>> +                          sed -i '/AlternativeNamesPolicy=/s/$/ mac/' ${D}${nonarch_libdir}/systemd/network/99-default.link
>>>>>> +                  fi
>>>>>
>>>>> My brain's sh parser says this is invalid because we're missing a
>>>>> closing fi for the outermost if block.
>>>>
>>>> Yes, my bad I must have removed it by mistake
>>>>
>>>>> I'm also a bit worried about this code snippet as it'll just not be
>>>>> tested or maintained once this gets merged.
>>>>
>>>> This snippet belongs to a release note for 5.3 so it already matches the Yocto
>>>> version? I will include the version of systemd version here at the time of
>>>> writing to give some more context.
>>>>
>>>
>>> Does this mean that we already know it's not going to be compatible with
>>> Wrynose?
>>>
>>> People are told to follow each migration manual between their current
>>> and target Yocto releases, so this will essentially be understood as
>>> "apply for any release starting from 5.3".
>>>
>>> We already saw how well maintained old example recipes were since we
>>> don't test them, I'm not sure it makes sense to have code snippets we'll
>>> likely never test as well?
>> 
>> A simpler approach could be to say:
>> 
>> """
>> To set the mac policy to systemd, modify the ``99-default-link.link`` file
>> provided by systemd in a ``.bbappend`` file to set the ``NamePolicy=`` and
>> ``AlternativeNamesPolicy=`` settings to "mac".
>> """
>> 
>> This should not require maintenance. Do you agree?
>> 
[...]
> We could simply say that when pni-names is unset, NamePolicy and 
> AlternativeNamesPolicy are unset. Otherwise, the systemd upstream 
> default is used.
>
> Maybe add a link to the manpage as well, via :manpage:`systemd.link(5)` 
> (not tested)?
>
> No better suggestion though :/

Yes, I think we both want to keep things simple. I'll send a v2 with a link to
the manpage and just mention the NamePolicy and AlternativeNamesPolicy options,
as you phrased it.

Thanks!
Antonin

-- 
Antonin Godard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com