On Wed, Jul 03, 2019 at 03:33:52PM +0200, Jiri Pirko wrote:

quoted

+/* notifications */
+
+typedef void (*ethnl_notify_handler_t)(struct net_device *dev,
+				       struct netlink_ext_ack *extack,
+				       unsigned int cmd, u32 req_mask,
+				       const void *data);
+
+static const ethnl_notify_handler_t ethnl_notify_handlers[] = {
+};
+
+void ethtool_notify(struct net_device *dev, struct netlink_ext_ack *extack,
+		    unsigned int cmd, u32 req_mask, const void *data)

What's "req_mask" ?

It's infomask to interpret the same way as if it came from request
header (the notification triggered by a SET request or its ioctl
equivalent uses the same format as corresponding GET_REPLY message and
is created by the same code). But it could be called infomask, I have no
strong opinion about that.

quoted

+{
+	if (unlikely(!ethnl_ok))
+		return;
+	ASSERT_RTNL();
+
+	if (likely(cmd < ARRAY_SIZE(ethnl_notify_handlers) &&
+		   ethnl_notify_handlers[cmd]))

How it could be null?

Notification message types share the enum with other kernel messages:

/* message types - kernel to userspace */
enum {
	ETHTOOL_MSG_KERNEL_NONE,
	ETHTOOL_MSG_STRSET_GET_REPLY,
	ETHTOOL_MSG_SETTINGS_GET_REPLY,
	ETHTOOL_MSG_SETTINGS_NTF,
	ETHTOOL_MSG_SETTINGS_SET_REPLY,
	ETHTOOL_MSG_INFO_GET_REPLY,
	ETHTOOL_MSG_PARAMS_GET_REPLY,
	ETHTOOL_MSG_PARAMS_NTF,
	ETHTOOL_MSG_NWAYRST_NTF,
	ETHTOOL_MSG_PHYSID_NTF,
	ETHTOOL_MSG_RESET_NTF,
	ETHTOOL_MSG_RESET_ACT_REPLY,
	ETHTOOL_MSG_RXFLOW_GET_REPLY,
	ETHTOOL_MSG_RXFLOW_NTF,
	ETHTOOL_MSG_RXFLOW_SET_REPLY,

	/* add new constants above here */
	__ETHTOOL_MSG_KERNEL_CNT,
	ETHTOOL_MSG_KERNEL_MAX = (__ETHTOOL_MSG_KERNEL_CNT - 1)
};

Only entries for *_NTF types are non-null in ethnl_notify_handlers[]:

static const ethnl_notify_handler_t ethnl_notify_handlers[] = {
	[ETHTOOL_MSG_SETTINGS_NTF]	= ethnl_std_notify,
	[ETHTOOL_MSG_PARAMS_NTF]	= ethnl_std_notify,
	[ETHTOOL_MSG_NWAYRST_NTF]	= ethnl_nwayrst_notify,
	[ETHTOOL_MSG_PHYSID_NTF]	= ethnl_physid_notify,
	[ETHTOOL_MSG_RESET_NTF]		= ethnl_reset_notify,
	[ETHTOOL_MSG_RXFLOW_NTF]	= ethnl_rxflow_notify,
};

If the check above fails, it means that kernel code tried to send
a notification with type which does not exist or is not a notification,
i.e. a bug in kernel; that's why the WARN_ONCE.

Michal

quoted

+		ethnl_notify_handlers[cmd](dev, extack, cmd, req_mask, data);
+	else
+		WARN_ONCE(1, "notification %u not implemented (dev=%s, req_mask=0x%x)\n",
+			  cmd, netdev_name(dev), req_mask);
+}
+EXPORT_SYMBOL(ethtool_notify);