Re: [RFC] net : add tx timestamp to packet mmap.

Hello.

On 12/13/2012 02:29 PM, Richard Cochran wrote:

On Wed, Dec 12, 2012 at 04:29:25PM +0100, Paul Chavent wrote:

quoted

This patch allow to generate tx timestamps of packets sent by the packet mmap interface.

Actually, you can't get tx timestamps with the sample code below.

I wonder if my current implementation is good. And if not, how should i get the timestamps ?

In order for time stamps to appear, somebody has to call
skb_tx_timestamp() ...

Yes. "Somebody" means "the hardware driver" after completing xmit. 
That's true ?

quoted

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index e639645..948748b 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c

@@ -1857,6 +1857,10 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
  	void *data;
  	int err;

+	err = sock_tx_timestamp(&po->sk, &skb_shinfo(skb)->tx_flags);

 >
 > and this call is only setting some flags.

Yes, it only sets some flags. I thought that those flags was required by 
the skb_tx_timestamp() in order to make the appropriate timestamping 
(hardware, software, etc).

So in order to have tx timestamp that work, both calls are needed ?

Why sock_tx_timestamp is called in packet_fill_skb and 
packet_sendmsg_spkt and not in tpacket_fill_skb ?
Why i can retrieve timestamps when i add this call ?

HTH,
Richard

Thank for your help.

Paul.