Re: [PATCH net-next v7 2/5] net: add a generation counter for dev->mc changes

[Nicolas Dichtel <nicolas.dichtel@6wind.com>]

Le 24/09/2026 à 03:15, Yuyang Huang a écrit :
> A multi-part RTM_GETMULTICAST dump of dev->mc resumes by position, so
> entries added or removed between two dump rounds can be skipped or
> repeated. The IPv4 and IPv6 dumps report that with NLM_F_DUMP_INTR by
> stamping cb->seq from a per netns generation counter combined with
> dev_base_seq, see inet_base_seq().
> 
> Add the equivalent for the device multicast lists: a per netns counter
> bumped whenever an entry is added to or removed from any dev->mc. The
> list helpers do not know which device a list belongs to, so give
> netdev_hw_addr_list an owner set for dev->mc only and bump the counter
> of dev_net(owner) where entries are created and freed. That covers the
> dev_mc_* helpers, both lists of a sync, the hardware sync helpers
> drivers call from their rx mode callbacks or their own workers and the
> reconciliation after an asynchronous rx mode update, while snapshot
> and other lists have no owner and are not tracked. It is atomic since
> the writers only hold the address lock of their own device.

For IPv4 and IPv6, the generation counter was initially used to invalidate some
caches; that's why it is global. Here, the goal is only to check the consistency
of the netlink dump. I wonder if maintaining a counter per list would not be
more straightforward.

A helper could then manage list->count and list->genid, both evolving together.