Re: [EVL] Kernel WARNING: notifier callback netevent_handler already registered

Am 27.04.26 um 11:18 schrieb Florian Bezdeka:
> On Sun, 2026-04-26 at 23:32 +0200, Hannes Diethelm wrote:
>> Am 26.04.26 um 21:24 schrieb Philippe Gerum:
>>> Hannes Diethelm <[email protected]> writes:
>>>
>>>> Am 25.04.26 um 20:50 schrieb Philippe Gerum:
>>>>> Hannes Diethelm <[email protected]> writes:
>>>>>
>>>>>> Hello
>>>>>>
>>>>>> There is a Kernel WARNING: "notifier callback netevent_handler already registered right after boot". It is repeated 5 times.
>>>>>>
>>>>>> Config:
>>>>>> Debian Trixie with xfce4 Desktop
>>>>>> libevl: r56
>>>>>> linux-evl: v6.12.67-evl2-rebase
>>>>>>
>>>>>> I traced the issue already trough the following code:
>>>>>> net/core/net_namespace.c:355
>>>>>> kernel/evl/net/net.c:35
>>>>>> kernel/evl/net/ipv4/ipv4.c:41
>>>>>> kernel/evl/net/ipv4/arp.c:323
>>>>>>
>>>>>> However, I lack the knowledge to do a proper fix. One way would be to just check in evl_net_init_arp() if it is already
>>>>>> registered and don't do it more than once but that doesn't feel right.
>>>>> It looks like the system is instantiating multiple network
>>>>> namespaces,
>>>>> for each of which we set up an ARP front cache by calling
>>>>> evl_net_init_arp(). Bad idea to hook a system-wide handler there as
>>>>> well. Could you confirm this fix [1] works for you?
>>>>> Thanks for reporting this.
>>>>> [1]
>>>>> https://gitlab.com/Xenomai/xenomai4/linux-evl/-/commit/569beef061321c2c00d775b13ad0aec1a1d2a416
>>>>>
>>>>
>>>> Thanks, that was fast. The WARNING is gone now.
>>>>
>>>> But now after just updating to the kernel including your fix, I have a different behavior on
>>>> incoming packages. It seams that the default when no filter is set has changed from EVL_RX_SKIP to EVL_RX_ACCEPT.
>>>>
>>>> linux-evl: v6.12.67-evl2-rebase
>>>> -After evl net -ei enp7s0, I can ping another host.
>>>> -oob-net-icmp does only receive packages when I use an eBPF filter with EVL_RX_ACCEPT
>>>> -After that, ping doesn't work any more
>>>>
>>>> linux-evl: v6.12.y-cip-evl-rebase
>>>> -After evl net -ei enp7s0, I can NOT ping another host.
>>>> -oob-net-icmp does receive packages
>>>> -If I use an eBPF filter returning EVL_RX_SKIP, I can ping again
>>>>
>>>> I am not using VLAN's.
>>>>
>>>> Was that changed on purpose?
>>>
>>> Yes, this is implemented by this commit [1]. The rationale here is that
>>> if you turn on the oob port directly on a base device, then the evl net
>>> stack may assume that the device is entirely dedicated to oob traffic,
>>> as opposed to enabling such port on some upper device based on the
>>> former (e.g. a VLAN interface). As a result, all ingress traffic
>>> received by such base device is diverted (RX_ACCEPT) to the evl net
>>> stack.
>>>
>>> [1] https://gitlab.com/Xenomai/xenomai4/linux-evl/-/commit/3026e69cee2a1de047818fa06ad8c44623461a0d
>>>
>>
>> This makes sense. It took me some time to get evl reading packages by
>> activating an eBPF filter and it's mostly save to assume that you don't
>> have mixed traffic on an real time network interface. With this change,
>> a filter is not needed any more.
>>
>> A bit off topic:
>>
>> Is there anything like rtping for evl? I have seen oob-net-icmp.c but
>> this is answering requests.
>>
>> In Xenomai3, there is a debian package configuration. Any interest in
>> one for libevl? I have one working but it's still very basic. If it's
>> presentable, I can send a patch.
> 
> There is a debianization for x4 in xenomai-images already. See [1].
> Can't tell why it hasn't been upstreamed yet. Maybe Tobias or Philippe
> can comment on that.
> 
> [1] https://gitlab.com/Xenomai/xenomai-images/-/tree/master/recipes-xenomai/libevl/files/debian

Thanks for the hint. This debianization is also basic, looks like it is only built for
CI purpose. But it helps to improve my version.

There are a few things missing:
- Build dependency's
- Optional: evl group + udev rules to allow non-root usage
- Probably much more for being a install & use debian package