Re: [PATCH iproute2 0/2] ip: ipstats: Fix statistics split across netlink messages

[Stephen Hemminger <stephen@networkplumber.org>]

On Sun, 30 Aug 2026 20:19:47 +0200
Alexander Zubkov <green@qrator.net> wrote:

> When dumping statistics, the kernel may split the statistics of a single
> interface across several netlink messages: if an attribute does not fit
> into the current skb, rtnl_fill_statsinfo() keeps the partial message and
> the dump is resumed at the same ifindex. "ip stats" formats every message
> on its own, so such an interface is reported twice and part of its
> statistics is lost. With "group offload subgroup l3_stats", which requests
> two attributes that the kernel emits one by one, this is easy to hit on a
> box with many netdevices:
> 
>     109: vlan859: group offload subgroup l3_stats on used on
> 
>     109: vlan859: group offload subgroup l3_stats
> 
> The first record holds IFLA_OFFLOAD_XSTATS_HW_S_INFO, the second one
> holds IFLA_OFFLOAD_XSTATS_L3_STATS, and the counters are never shown.
> 
> Patch 1 reassembles such messages before formatting them. Patch 2 is an
> unrelated hardening cleanup and can be dropped.
> 
> The merge itself was also exercised out of tree against the two message
> shapes the kernel can split, offload xstats cut between HW_S_INFO and
> L3_STATS, and bridge per-VLAN xstats cut between two BRIDGE_XSTATS_VLAN
> entries, plus a layout that must be refused rather than merged.
> 
> I faced the issue on kernel 7.1.5 / iproute2-7.0.0, mlxsw switch, with
> ~120 netdevices. The split was visible in an strace as two RTM_NEWSTATS
> messages with the same ifindex, carrying IFLA_OFFLOAD_XSTATS_HW_S_INFO
> and IFLA_OFFLOAD_XSTATS_L3_STATS respectively. The further research,
> patches and supporting texts was prepared with the help of an AI
> assistant. I reviewed and tested the patches against iproute2-7.1.0, with
> the proposed patches the interface is correctly reported once, with its
> counters. Although the patches makes sense to me, I have little
> experience with netlink handling.
> 
> 
> Alexander Zubkov (2):
>   ip: ipstats: Merge statistics split across several netlink messages
>   ip: ipstats: Do not hide HW statistics when hw_stats_info is missing
> 
>  ip/ipstats.c | 285 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 280 insertions(+), 5 deletions(-)
> 


Please write patches for humans not AI.
Tell Claude to be concise and terse and follow patterns of other code
in the same project.