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

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