ptp: Add generic PTP is_sync() function

PHY drivers such as micrel or dp83640 need to analyze whether a given
skb is a PTP sync message for one step functionality.

In order to avoid code duplication introduce a generic function and
move it to ptp classify.

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

include/linux/ptp_classify.h

···
 	return msgtype;
 }
 
+/**
+ * ptp_msg_is_sync - Evaluates whether the given skb is a PTP Sync message
+ * @skb: packet buffer
+ * @type: type of the packet (see ptp_classify_raw())
+ *
+ * This function evaluates whether the given skb is a PTP Sync message.
+ *
+ * Return: true if sync message, false otherwise
+ */
+bool ptp_msg_is_sync(struct sk_buff *skb, unsigned int type);
+
 void __init ptp_classifier_init(void);
 #else
 static inline void ptp_classifier_init(void)
···
 	 * executed since no available header from ptp_parse_header.
 	 */
 	return PTP_MSGTYPE_SYNC;
+}
+static inline bool ptp_msg_is_sync(struct sk_buff *skb, unsigned int type)
+{
+	return false;
 }
 #endif
 #endif /* _PTP_CLASSIFY_H_ */

net/core/ptp_classifier.c

···
 }
 EXPORT_SYMBOL_GPL(ptp_parse_header);
 
+bool ptp_msg_is_sync(struct sk_buff *skb, unsigned int type)
+{
+	struct ptp_header *hdr;
+
+	hdr = ptp_parse_header(skb, type);
+	if (!hdr)
+		return false;
+
+	return ptp_get_msgtype(hdr, type) == PTP_MSGTYPE_SYNC;
+}
+EXPORT_SYMBOL_GPL(ptp_msg_is_sync);
+
 void __init ptp_classifier_init(void)
 {
 	static struct sock_filter ptp_filter[] __initdata = {