[PATCH net-next v2 0/3] net: bridge: cfm: notify userspace on CFM config changes

[Abdul Wasey <w453y.me@gmail.com>]

CFM status changes are sent to userspace, config changes are not, so
the only way to see a MEP being created, a peer added or CCM
transmission started is to poll RTM_GETLINK. Patch 3 adds the
notification. Patches 1 and 2 fix the two problems the AI review found
in v1.

Patch 1 makes br_get_link_af_size_filtered() count the CFM config
attributes. Without it the notification overflows its skb once a MEP
has about 32 peers, and br_info_notify() hits its WARN_ON. Patch 2 puts
an empty IFLA_BRIDGE_CFM nest in the message when the bridge has no
MEPs, so deleting the last MEP is visible to a listener.

Tested with virtme-ng on net-next: 300 peer MEPs and config changes
give one notification each (6248 byte CFM payload) and no warning;
deleting the last MEP gives a notification with an empty
IFLA_BRIDGE_CFM; a request that fails before changing anything sends
nothing, one that fails half way still sends one. Also built with
CONFIG_BRIDGE_CFM off.

v2:
- new patch 1, count the config attributes in the message size
- new patch 2, empty CFM nest for a bridge with no MEPs
- patch 3: unchanged, rebased on current net-next

v1: https://lore.kernel.org/netdev/20261004041320.2684045-1-w453y.me@gmail.com/

Abdul Wasey (3):
  net: bridge: cfm: count CFM config attributes in the link message size
  net: bridge: cfm: send an empty CFM nest when a bridge has no MEPs
  net: bridge: cfm: notify userspace on CFM config changes

 net/bridge/br_cfm_netlink.c | 32 ++++++++++++++++++-------
 net/bridge/br_netlink.c     | 47 ++++++++++++++++++++++++++++++++++---
 2 files changed, 67 insertions(+), 12 deletions(-)

-- 
2.53.0