HSR forwards all packets it received on slave port A to slave port B and
one of the possible two copies to the user (master) interface.
In terms of PTP this is not good because the latency introduced by
forwarding makes the timestamp in the PTP packet inaccurate.

Introduce a hsr_ptp field to struct skb_shared_info which can be used to
store HSR specific information for sending and receiving skbs.

Receive (slave ports):
- HSR_PT_SLAVE_A/ HSR_PT_SLAVE_B to denote the port which received the
  packet. This information is only added to PTP packets.

Send (master port):
- HSR_PT_SLAVE_A/ HSR_PT_SLAVE_B to denote the port on which the packet
  has to be sent.
- HSR_SKB_INCLUDES_HEADER to denote that the packet already contains a
  HSR header and the stack must not add the system's header to it.

HSR_SKB_INCLUDES_HEADER is used to allow forwarding a PTP packet and
preserving the HSR header by the sender.
Cloning skbs requires to preserve the socket information so that a PTP
timestamp can be associated with the socket.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/if_hsr.h |   2 +
 include/linux/skbuff.h |   1 +
 net/hsr/hsr_device.c   |   7 +++
 net/hsr/hsr_forward.c  | 114 ++++++++++++++++++++++++++++++++++++++++++++++---
 net/hsr/hsr_slave.c    |  16 +++++++
 5 files changed, 133 insertions(+), 7 deletions(-)

diff --git a/include/linux/if_hsr.h b/include/linux/if_hsr.h
index f4cf2dd36d193..1463ddbc8cddf 100644
--- a/include/linux/if_hsr.h
+++ b/include/linux/if_hsr.h

@@ -22,6 +22,8 @@ enum hsr_port_type {
 	HSR_PT_PORTS,	/* This must be the last item in the enum */
 };
 
+#define HSR_SKB_INCLUDES_HEADER		(1 << 4)
+
 /* HSR Tag.
  * As defined in IEC-62439-3:2010, the HSR tag is really { ethertype = 0x88FB,
  * path, LSDU_size, sequence Nr }. But we let eth_header() create { h_dest,

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 86737076101d4..52c847e490ee8 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h

@@ -605,6 +605,7 @@ struct skb_shared_info {
 	};
 	unsigned int	gso_type;
 	u32		tskey;
+	u32		hsr_ptp;