RFC Add support for warnings to extack

Currently we have the limitation that warnings cannot be reported though extack. For example, when tc flower failed to get offloaded but got installed on software datapath. The hardware failure is not fatal and thus extack is not even shared with the driver, so the error is simply omitted from any logging.

The idea here is to allow such kind of warnings to get through and be available for the sysadmin or the tool managing such commands (like Open vSwitch), so that if this happens, we will have such log message in a file later.

The first patch extends extack to support more than one message and with different log level (currently only error and warning). The second shares extack with the drivers regardless of skip_sw.

The iproute patch also follows.

This kernel change is backward compatible with older iproute because iproute will only process the last message, which should be the error one in case of failure, or a warning if it suceeded.

The iproute change is compatible with older kernels because it will find only one message to be processed and will handle it properly.

With this patches, this is now possible:

# tc qdisc add dev p7p1 ingress
# tc filter add dev p7p1 parent ffff: protocol ip prio 1 flower \
	src_mac ec:13:db:00:00:00 dst_mac ec:14:c2:00:00:00 \
	src_ip 56.0.0.0 dst_ip 55.0.0.0 action drop
Warning: TC offload is disabled on net device.
# echo $?
0

Marcelo Ricardo Leitner (2):
netlink: extend extack so it can carry more than one message
sched: pass extack through even if skip_sw is not set

 include/linux/netlink.h  | 50 +++++++++++++++++++++++++++++-------------------
 include/net/pkt_cls.h    |  3 +--
 net/netlink/af_netlink.c | 12 +++++++-----
 3 files changed, 38 insertions(+), 27 deletions(-)

2.14.3