netdev - Re: [PATCH 1/3] netlink: Add notifier when changing netlink socket membership

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Date: Wed, 31 Jan 2024 17:40:56 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>
Cc: linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rafael@...nel.org>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, Ricardo Neri
 <ricardo.neri-calderon@...ux.intel.com>, Daniel Lezcano
 <daniel.lezcano@...aro.org>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org
Subject: Re: [PATCH 1/3] netlink: Add notifier when changing netlink socket
 membership

On Wed, 31 Jan 2024 13:05:33 +0100 Stanislaw Gruszka wrote:
> Add notification when adding/removing multicast group to/from
> client socket via setsockopt() syscall.
> 
> It can be used with conjunction with netlink_has_listeners() to check
> if consumers of netlink multicast messages emerge or disappear.
> 
> A client can call netlink_register_notifier() to register a callback.
> In the callback check for state NETLINK_CHANGE and NETLINK_URELEASE to
> get notification for change in the netlink socket membership.
> 
> Thus, a client can now send events only when there are active consumers,
> preventing unnecessary work when none exist.

Can we plumb thru the existing netlink_bind / netlink_unbind callbacks?
Add similar callbacks to the genl family struct to plumb it thru to
thermal. Then thermal can do what it wants with it (also add driver
callbacks or notifiers).

Having a driver listen to a core AF_NETLINK notifier to learn about
changes to a genl family it registers with skips too many layers to
easily reason about. At least for my taste.

When you repost please CC Florian W, Johannes B and Jiri P, off the top
of my head. Folks who most often work on netlink internals..