PACKET socket can retain its fanout membership through link down and up
and leave a fanout while closed regardless of link state.
However, socket was forbidden from joining a fanout while it was not
RUNNING.

This patch allows PACKET socket to join a fanout while not RUNNING.
Selftest psock_fanout is extended to test this scenario.
This is the only test that was performed.

This scenario was identified while studying DPDK pmd_af_packet_drv.
Since sockets are only created during initialization, there is no reason
to fail the initialization if a single link is temporarily down.

I hope it is not considered as breaking user space and that applications
are not designed to expect this failure.


Changes:

V02:
* psock_fanout: use explicit loopback up/down instead of toggle.
* psock_fanout: don't try to restore loopback state on failure.
* Rephrase commit message about "leaving a fanout".

V01: https://lore.kernel.org/netdev/cover.1728303615.git.gur.stavi@huawei.com/

Gur Stavi (2):
  af_packet: allow fanout_add when socket is not RUNNING
  selftests: net/psock_fanout: socket joins fanout when link is down

 net/packet/af_packet.c                     | 10 +++---
 tools/testing/selftests/net/psock_fanout.c | 42 ++++++++++++++++++++--
 2 files changed, 44 insertions(+), 8 deletions(-)


base-commit: f95b4725e796b12e5f347a0d161e1d3843142aa8
-- 
2.45.2