netdev - Re: [RFC] af_packet: allow disabling timestamps

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Date:	Thu, 13 Sep 2007 14:24:06 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	Unai Uribarri <unai.uribarri@...enet.com>,
	"David S. Miller" <davem@...emloft.net>,
	Evgeniy Polyakov <johnpol@....mipt.ru>, netdev@...r.kernel.org
Subject: Re: [RFC] af_packet: allow disabling timestamps

On Thu, 13 Sep 2007 12:42:53 +0200
Stephen Hemminger <shemminger@...ux-foundation.org> wrote:

> Currently, af_packet does not allow disabling timestamps. This patch changes
> that but doesn't force global timestamps on.
> 
> This shows up in bugzilla as:
> 	http://bugzilla.kernel.org/show_bug.cgi?id=4809
> 
> Patch against net-2.6.24 tree.
> 

I am not sure I understood this patch.

This means that tcpdump/ethereal wont get precise timestamps 
(gathered when packet is received), but imprecise ones (gathered when the sniffer reads the packet)

I added some time ago ktime infrastructure to eventually get nanosecond 
precision in libpcap, so I would prefer a step in the right direction :)

Should'nt we use something like :

[PATCH] af_packet : allow disabling timestamps, or requesting nanosecond precision.

Signed-off-by: Eric Dumazet <dada1@...mosbay.com>

diff --git a/net/core/sock.c b/net/core/sock.c
index 5a16e38..1c10b9d 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -563,6 +563,7 @@ set_rcvbuf:
 		} else {
 			sock_reset_flag(sk, SOCK_RCVTSTAMP);
 			sock_reset_flag(sk, SOCK_RCVTSTAMPNS);
+			sock_disable_timestamp(sk);
 		}
 		break;
 
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 745e2cb..409de44 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -650,12 +650,27 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev, struct packe
 	h->tp_snaplen = snaplen;
 	h->tp_mac = macoff;
 	h->tp_net = netoff;
-	if (skb->tstamp.tv64)
-		tv = ktime_to_timeval(skb->tstamp);
-	else
-		do_gettimeofday(&tv);
-	h->tp_sec = tv.tv_sec;
-	h->tp_usec = tv.tv_usec;
+	h->tp_sec = 0;
+	h->tp_usec = 0;
+	if ((sock_flag(sk, SOCK_TIMESTAMP))) {
+		if (sock_flag(sk, SOCK_RCVTSTAMPNS)) {
+			struct timespec ts;
+			if (skb->tstamp.tv64)
+				ts = ktime_to_timespec(skb->tstamp);
+			else
+				getnstimeofday(&ts);
+			h->tp_sec = ts.tv_sec;
+			h->tp_usec = ts.tv_nsec; /* cheat a litle bit */
+		}
+		else {
+			if (skb->tstamp.tv64)
+				tv = ktime_to_timeval(skb->tstamp);
+			else
+				do_gettimeofday(&tv);
+			h->tp_sec = tv.tv_sec;
+			h->tp_usec = tv.tv_usec;
+		}
+	}
 
 	sll = (struct sockaddr_ll*)((u8*)h + TPACKET_ALIGN(sizeof(*h)));
 	sll->sll_halen = 0;
@@ -1014,6 +1029,7 @@ static int packet_create(struct net *net, struct socket *sock, int protocol)
 		sock->ops = &packet_ops_spkt;
 
 	sock_init_data(sock, sk);
+	sock_enable_timestamp(sk);
 
 	po = pkt_sk(sk);
 	sk->sk_family = PF_PACKET;
-
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