Linux 4.20 / incomplete ipv4 addr list / RTM_GETADDR

[Arthur Gautier]

On Sat, Dec 29, 2018 at 05:54:58AM +0000, Arthur Gautier wrote:
> On Fri, Dec 28, 2018 at 07:52:59PM +0100, Ondrej Zajicek wrote:
> > On Thu, Dec 27, 2018 at 05:01:52PM +0000, Arthur Gautier wrote:
> > > Hello bird users,
> > > 
> > > Today I tried to upgrade one of platform to from linux 4.19 to linux 4.20.
> > > I started noticing the bgp protocol could not start after this message:
> > >   <TRACE> uplink: Waiting for 1.2.3.4 to become my neighbor
> > > 
> > > The neighbor (directly connected on an interface) would never appear to
> > > bird (as in show interfaces) because the AF_INET/RTM_GETADDR reply from the
> > > kernel looks incomplete. It works fine in v6.
> > > 
> > > The results from kernel are capped to 104 ip address (and we run servers
> > > with >700 ip address) on loopback.
> > 
> > Hello
> > 
> > Aren't there any error messages in log? I would guess it is truncated
> > message due to some more information pushed from kernel or putting
> > multiple information into one messsage.
> > 
> > Does it help if the constant NL_RX_SIZE (in sysdep/linux/netlink.c) is
> > increased?
> > 
> > > I confirm this behavour with nlmon / tcpdump / wireshark.
> > > Tested with bird v2.0.2 and v1.6.3 (debian stable).
> > 
> > Is capped the result from kernel, or its parsing in BIRD? But
> > perhaps limited buffer size would cause kernel to limit output
> > of data it sends.
> 
> The result from the kernel is capped. I extracted the bird code
> to reproduce the issue in a minimal environment. I also have been able
> to bisected the issue I have down to d7e38611b81e6d7e14969c361f2b9fc07403a6c3
> https://github.com/torvalds/linux/commit/d7e38611b81e6d7e14969c361f2b9fc07403a6c3
> 
> I am not yet capable to understand why this is happening. Code looks
> very similar to what ipv6 is doing but does not work the same for v4.
> 
> I am still working on getting a patch for this.
>~

FYI, here is a patch on linux that fixes my issue:
  https://patchwork.ozlabs.org/patch/1019459/

This patch being my first I contribute to linux, I'm quite inexperienced with
the process. Hopefuly I did it correctly (and the patch is correct!).

-- 
\o/ Arthur
 G  Gandi.net