Merge branch 'ethtool-extack'

Jakub Kicinski says:

====================
net: support extack in dump and simplify ethtool uAPI

Ethtool currently requires header nest to be always present even if
it doesn't have to carry any attr for a given request. This inflicts
unnecessary pain on the users.

What makes it worse is that extack was not working in dump's ->start()
callback. Address both of those issues.
====================

Signed-off-by: David S. Miller <[e-mail]>

include/linux/netlink.h

···
 	int (*start)(struct netlink_callback *);
 	int (*dump)(struct sk_buff *skb, struct netlink_callback *);
 	int (*done)(struct netlink_callback *);
+	struct netlink_ext_ack *extack;
 	void *data;
 	struct module *module;
 	u32 min_dump_alloc;

net/ethtool/netlink.c

···
 	int ret;
 
 	if (!header) {
+		if (!require_dev)
+			return 0;
 		NL_SET_ERR_MSG(extack, "request header missing");
 		return -EINVAL;
 	}

net/netlink/af_netlink.c

···
 	cb->strict_check = !!(nlk2->flags & NETLINK_F_STRICT_CHK);
 
 	if (control->start) {
+		cb->extack = control->extack;
 		ret = control->start(cb);
+		cb->extack = NULL;
 		if (ret)
 			goto error_put;
 	}

net/netlink/genetlink.c

···
 			.start = genl_start,
 			.dump = genl_lock_dumpit,
 			.done = genl_lock_done,
+			.extack = extack,
 		};
 
 		genl_unlock();
···
 			.start = genl_start,
 			.dump = ops->dumpit,
 			.done = genl_parallel_done,
+			.extack = extack,
 		};
 
 		err = __netlink_dump_start(net->genl_sock, skb, nlh, &c);