Tue, Jul 02, 2019 at 01:50:24PM CEST, mkubecek@suse.cz wrote:

[...]

+/* The structure holding data for unified processing GET requests consists of
+ * two parts: request info and reply data. Request info is related to client
+ * request and for dump request it stays constant through all processing;
+ * reply data contains data for composing a reply message. When processing
+ * a dump request, request info is filled only once but reply data is filled
+ * from scratch for each reply message.
+ *
+ * +-----------------+-----------------+------------------+-----------------+
+ * | common_req_info |  specific info  | ethnl_reply_data |  specific data  |
+ * +-----------------+-----------------+------------------+-----------------+
+ * |<---------- request info --------->|<----------- reply data ----------->|
+ *
+ * Request info always starts at offset 0 with struct ethnl_req_info which
+ * holds information from parsing the common header. It may be followed by
+ * other members for request attributes specific for current message type.
+ * Reply data starts with struct ethnl_reply_data which may be followed by
+ * other members holding data needed to compose a message.
+ */
+

[...]

+/**
+ * struct get_request_ops - unified handling of GET requests
+ * @request_cmd:      command id for request (GET)
+ * @reply_cmd:        command id for reply (GET_REPLY)
+ * @hdr_attr:         attribute type for request header
+ * @max_attr:         maximum (top level) attribute type
+ * @data_size:        total length of data structure
+ * @repdata_offset:   offset of "reply data" part (struct ethnl_reply_data)

For example, this looks quite scarry for me. You have one big chunk of
data (according to the scheme above) specific for cmd with reply starting
at arbitrary offset.

+ * @request_policy:   netlink policy for message contents
+ * @header_policy:    (optional) netlink policy for request header
+ * @default_infomask: default infomask (to use if none specified)
+ * @all_reqflags:     allowed request specific flags
+ * @allow_nodev_do:   allow non-dump request with no device identification
+ * @parse_request:
+ *	Parse request except common header (struct ethnl_req_info). Common
+ *	header is already filled on entry, the rest up to @repdata_offset
+ *	is zero initialized. This callback should only modify type specific
+ *	request info by parsed attributes from request message.
+ * @prepare_data:
+ *	Retrieve and prepare data needed to compose a reply message. Calls to
+ *	ethtool_ops handlers should be limited to this callback. Common reply
+ *	data (struct ethnl_reply_data) is filled on entry, type specific part
+ *	after it is zero initialized. This callback should only modify the
+ *	type specific part of reply data. Device identification from struct
+ *	ethnl_reply_data is to be used as for dump requests, it iterates
+ *	through network devices which common_req_info::dev points to the
+ *	device from client request.
+ * @reply_size:
+ *	Estimate reply message size. Returned value must be sufficient for
+ *	message payload without common reply header. The callback may returned
+ *	estimate higher than actual message size if exact calculation would
+ *	not be worth the saved memory space.
+ * @fill_reply:
+ *	Fill reply message payload (except for common header) from reply data.
+ *	The callback must not generate more payload than previously called
+ *	->reply_size() estimated.
+ * @cleanup:
+ *	Optional cleanup called when reply data is no longer needed. Can be
+ *	used e.g. to free any additional data structures outside the main
+ *	structure which were allocated by ->prepare_data(). When processing
+ *	dump requests, ->cleanup() is called for each message.
+ *
+ * Description of variable parts of GET request handling when using the unified
+ * infrastructure. When used, a pointer to an instance of this structure is to
+ * be added to &get_requests array and generic handlers ethnl_get_doit(),
+ * ethnl_get_dumpit(), ethnl_get_start() and ethnl_get_done() used in
+ * @ethnl_genl_ops
+ */
+struct get_request_ops {
+	u8			request_cmd;
+	u8			reply_cmd;
+	u16			hdr_attr;
+	unsigned int		max_attr;
+	unsigned int		data_size;
+	unsigned int		repdata_offset;
+	const struct nla_policy *request_policy;
+	const struct nla_policy *header_policy;
+	u32			default_infomask;
+	u32			all_reqflags;
+	bool			allow_nodev_do;
+
+	int (*parse_request)(struct ethnl_req_info *req_info,
+			     struct nlattr **tb,
+			     struct netlink_ext_ack *extack);
+	int (*prepare_data)(struct ethnl_req_info *req_info,
+			    struct genl_info *info);
+	int (*reply_size)(const struct ethnl_req_info *req_info);
+	int (*fill_reply)(struct sk_buff *skb,
+			  const struct ethnl_req_info *req_info);
+	void (*cleanup)(struct ethnl_req_info *req_info);
+};
+
#endif /* _NET_ETHTOOL_NETLINK_H */
-- 
2.22.0