ptp: Add generic ptp v2 header parsing function

Reason: A lot of the ptp drivers - which implement hardware time stamping - need
specific fields such as the sequence id from the ptp v2 header. Currently all
drivers implement that themselves.

Introduce a generic function to retrieve a pointer to the start of the ptp v2
header.

Suggested-by: Russell King <[e-mail]>
Signed-off-by: Kurt Kanzenbach <[e-mail]>
Reviewed-by: Richard Cochran <[e-mail]>
Reviewed-by: Florian Fainelli <[e-mail]>
Reviewed-by: Russell King <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/ptp_classify.h

···
 #define OFF_IHL		14
 #define IPV4_HLEN(data) (((struct iphdr *)(data + OFF_IHL))->ihl << 2)
 
+struct clock_identity {
+	u8 id[8];
+} __packed;
+
+struct port_identity {
+	struct clock_identity	clock_identity;
+	__be16			port_number;
+} __packed;
+
+struct ptp_header {
+	u8			tsmt;  /* transportSpecific | messageType */
+	u8			ver;   /* reserved          | versionPTP  */
+	__be16			message_length;
+	u8			domain_number;
+	u8			reserved1;
+	u8			flag_field[2];
+	__be64			correction;
+	__be32			reserved2;
+	struct port_identity	source_port_identity;
+	__be16			sequence_id;
+	u8			control;
+	u8			log_message_interval;
+} __packed;
+
 #if defined(CONFIG_NET_PTP_CLASSIFY)
 /**
  * ptp_classify_raw - classify a PTP packet
···
  */
 unsigned int ptp_classify_raw(const struct sk_buff *skb);
 
+/**
+ * ptp_parse_header - Get pointer to the PTP v2 header
+ * @skb: packet buffer
+ * @type: type of the packet (see ptp_classify_raw())
+ *
+ * This function takes care of the VLAN, UDP, IPv4 and IPv6 headers. The length
+ * is checked.
+ *
+ * Note, internally skb_mac_header() is used. Make sure that the @skb is
+ * initialized accordingly.
+ *
+ * Return: Pointer to the ptp v2 header or NULL if not found
+ */
+struct ptp_header *ptp_parse_header(struct sk_buff *skb, unsigned int type);
+
 void __init ptp_classifier_init(void);
 #else
 static inline void ptp_classifier_init(void)
···
 static inline unsigned int ptp_classify_raw(struct sk_buff *skb)
 {
 	return PTP_CLASS_NONE;
+}
+static inline struct ptp_header *ptp_parse_header(struct sk_buff *skb,
+						  unsigned int type)
+{
+	return NULL;
 }
 #endif
 #endif /* _PTP_CLASSIFY_H_ */

net/core/ptp_classifier.c

···
 }
 EXPORT_SYMBOL_GPL(ptp_classify_raw);
 
+struct ptp_header *ptp_parse_header(struct sk_buff *skb, unsigned int type)
+{
+	u8 *ptr = skb_mac_header(skb);
+
+	if (type & PTP_CLASS_VLAN)
+		ptr += VLAN_HLEN;
+
+	switch (type & PTP_CLASS_PMASK) {
+	case PTP_CLASS_IPV4:
+		ptr += IPV4_HLEN(ptr) + UDP_HLEN;
+		break;
+	case PTP_CLASS_IPV6:
+		ptr += IP6_HLEN + UDP_HLEN;
+		break;
+	case PTP_CLASS_L2:
+		break;
+	default:
+		return NULL;
+	}
+
+	ptr += ETH_HLEN;
+
+	/* Ensure that the entire header is present in this packet. */
+	if (ptr + sizeof(struct ptp_header) > skb->data + skb->len)
+		return NULL;
+
+	return (struct ptp_header *)ptr;
+}
+EXPORT_SYMBOL_GPL(ptp_parse_header);
+
 void __init ptp_classifier_init(void)
 {
 	static struct sock_filter ptp_filter[] __initdata = {