packet_mmap: expose hw packet timestamps to network packet capture utilities

This patch adds a setting, PACKET_TIMESTAMP, to specify the packet
timestamp source that is exported to capture utilities like tcpdump by
packet_mmap.

PACKET_TIMESTAMP accepts the same integer bit field as
SO_TIMESTAMPING. However, only the SOF_TIMESTAMPING_SYS_HARDWARE and
SOF_TIMESTAMPING_RAW_HARDWARE values are currently recognized by
PACKET_TIMESTAMP. SOF_TIMESTAMPING_SYS_HARDWARE takes precedence over
SOF_TIMESTAMPING_RAW_HARDWARE if both bits are set.

If PACKET_TIMESTAMP is not set, a software timestamp generated inside
the networking stack is used (the behavior before this setting was
added).

Signed-off-by: Scott McMillan <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/networking/packet_mmap.txt

···
     pfd.events = POLLOUT;
     retval = poll(&pfd, 1, timeout);
 
+-------------------------------------------------------------------------------
++ PACKET_TIMESTAMP
+-------------------------------------------------------------------------------
+
+The PACKET_TIMESTAMP setting determines the source of the timestamp in
+the packet meta information.  If your NIC is capable of timestamping
+packets in hardware, you can request those hardware timestamps to used.
+Note: you may need to enable the generation of hardware timestamps with
+SIOCSHWTSTAMP.
+
+PACKET_TIMESTAMP accepts the same integer bit field as
+SO_TIMESTAMPING.  However, only the SOF_TIMESTAMPING_SYS_HARDWARE
+and SOF_TIMESTAMPING_RAW_HARDWARE values are recognized by
+PACKET_TIMESTAMP.  SOF_TIMESTAMPING_SYS_HARDWARE takes precedence over
+SOF_TIMESTAMPING_RAW_HARDWARE if both bits are set.
+
+    int req = 0;
+    req |= SOF_TIMESTAMPING_SYS_HARDWARE;
+    setsockopt(fd, SOL_PACKET, PACKET_TIMESTAMP, (void *) &req, sizeof(req))
+
+If PACKET_TIMESTAMP is not set, a software timestamp generated inside
+the networking stack is used (the behavior before this setting was added).
+
+See include/linux/net_tstamp.h and Documentation/networking/timestamping
+for more information on hardware timestamps.
+
 --------------------------------------------------------------------------------
 + THANKS
 --------------------------------------------------------------------------------

include/linux/if_packet.h

···
 #define PACKET_LOSS			14
 #define PACKET_VNET_HDR			15
 #define PACKET_TX_TIMESTAMP		16
+#define PACKET_TIMESTAMP		17
 
 struct tpacket_stats {
 	unsigned int	tp_packets;

net/packet/af_packet.c

···
 #include <linux/if_vlan.h>
 #include <linux/virtio_net.h>
 #include <linux/errqueue.h>
+#include <linux/net_tstamp.h>
 
 #ifdef CONFIG_INET
 #include <net/inet_common.h>
···
 	unsigned int		tp_hdrlen;
 	unsigned int		tp_reserve;
 	unsigned int		tp_loss:1;
+	unsigned int		tp_tstamp;
 	struct packet_type	prot_hook ____cacheline_aligned_in_smp;
 };
 
···
 	struct sk_buff *copy_skb = NULL;
 	struct timeval tv;
 	struct timespec ts;
+	struct skb_shared_hwtstamps *shhwtstamps = skb_hwtstamps(skb);
 
 	if (skb->pkt_type == PACKET_LOOPBACK)
 		goto drop;
···
 		h.h1->tp_snaplen = snaplen;
 		h.h1->tp_mac = macoff;
 		h.h1->tp_net = netoff;
-		if (skb->tstamp.tv64)
+		if ((po->tp_tstamp & SOF_TIMESTAMPING_SYS_HARDWARE)
+				&& shhwtstamps->syststamp.tv64)
+			tv = ktime_to_timeval(shhwtstamps->syststamp);
+		else if ((po->tp_tstamp & SOF_TIMESTAMPING_RAW_HARDWARE)
+				&& shhwtstamps->hwtstamp.tv64)
+			tv = ktime_to_timeval(shhwtstamps->hwtstamp);
+		else if (skb->tstamp.tv64)
 			tv = ktime_to_timeval(skb->tstamp);
 		else
 			do_gettimeofday(&tv);
···
 		h.h2->tp_snaplen = snaplen;
 		h.h2->tp_mac = macoff;
 		h.h2->tp_net = netoff;
-		if (skb->tstamp.tv64)
+		if ((po->tp_tstamp & SOF_TIMESTAMPING_SYS_HARDWARE)
+				&& shhwtstamps->syststamp.tv64)
+			ts = ktime_to_timespec(shhwtstamps->syststamp);
+		else if ((po->tp_tstamp & SOF_TIMESTAMPING_RAW_HARDWARE)
+				&& shhwtstamps->hwtstamp.tv64)
+			ts = ktime_to_timespec(shhwtstamps->hwtstamp);
+		else if (skb->tstamp.tv64)
 			ts = ktime_to_timespec(skb->tstamp);
 		else
 			getnstimeofday(&ts);
···
 		po->has_vnet_hdr = !!val;
 		return 0;
 	}
+	case PACKET_TIMESTAMP:
+	{
+		int val;
+
+		if (optlen != sizeof(val))
+			return -EINVAL;
+		if (copy_from_user(&val, optval, sizeof(val)))
+			return -EFAULT;
+
+		po->tp_tstamp = val;
+		return 0;
+	}
 	default:
 		return -ENOPROTOOPT;
 	}
···
 		if (len > sizeof(unsigned int))
 			len = sizeof(unsigned int);
 		val = po->tp_loss;
+		data = &val;
+		break;
+	case PACKET_TIMESTAMP:
+		if (len > sizeof(int))
+			len = sizeof(int);
+		val = po->tp_tstamp;
 		data = &val;
 		break;
 	default: