From mboxrd@z Thu Jan 1 00:00:00 1970 From: Willem de Bruijn Subject: Re: [PATCH] net-timestamp: Fix a documentation typo Date: Mon, 24 Nov 2014 17:38:21 -0500 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Network Development , "David S. Miller" To: Andy Lutomirski Return-path: Received: from mail-qa0-f43.google.com ([209.85.216.43]:49646 "EHLO mail-qa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751111AbaKXWiw (ORCPT ); Mon, 24 Nov 2014 17:38:52 -0500 Received: by mail-qa0-f43.google.com with SMTP id bm13so7197311qab.30 for ; Mon, 24 Nov 2014 14:38:51 -0800 (PST) In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: >>> Is user code supposed to rely on this and, further, on the fact that the >>> counter starts at zero? If not, how else is user code supposed to match >>> outgoing data to timestamps? >> >> That is correct. The per-socket counter is reset when >> SOF_TIMESTAMPING_OPT_ID is set. On datagram sockets, it returns the >> packet number since the reset. On stream sockets, it returns the byte >> offset since the reset. >> > > It might be worth tweaking the docs at some point to make this clearer. Good point. The commit message is apparently more informative than the actual documentation. >>> Also, is it intentional that the payload data associated with the tx >>> timestamp is (I think) the full outgoing packet including lower-layer >>> headers? >> >> Absolutely not. I'll look into that right away. It doesn't on ACK, and >> should certainly not expose this info in the other cases, either. > > Then I won't start trying to decode it :) The datagram feature existed before I added the counter and stream support, so returning the entire packet in that case is legacy behavior, I suppose. I did not intend to expose network headers for the new stream socket interface, though. > TBH, all I looked at was the packet size, which matched the full > link-layer packet. > > Also, the address returned by recvmsg appeared to be garbage instead > of 0.0.0.0 (or something meaningful, whatever that would be). > >> >>> And, finally, would it be possible to attach IP_PKTINFO to the looped >>> timestamp? That way I could finally update my fancy ping program to >>> track which outgoing interface was used for a request. >> >> If socket option IP_PKTINFO is set, you want to receive in_pktinfo for >> any packet that happens to be queued onto the error queue? Both >> SKB_EXT_ERR(skb) and PKTINFO_SKB_CB(skb) use the control block to >> store data that is later encoded in a cmsg, so there may not be enough >> room to hold both. I'll take a look. > > I don't really care what the mechanism is, but it would be really nice > if I could see what interface the send timestamp is associated with. Okay. I'll see if I can cook something up. > Also, thanks for this new feature. It's great! Thanks! > --Andy