From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-vb0-f53.google.com ([209.85.212.53]:33202 "EHLO mail-vb0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751019Ab3LPVzj (ORCPT ); Mon, 16 Dec 2013 16:55:39 -0500 Received: by mail-vb0-f53.google.com with SMTP id o19so3510545vbm.40 for ; Mon, 16 Dec 2013 13:55:38 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: <1387142056-21850-1-git-send-email-twpedersen@gmail.com> <1387142056-21850-2-git-send-email-twpedersen@gmail.com> From: Sergey Ryazanov Date: Tue, 17 Dec 2013 01:55:17 +0400 Message-ID: (sfid-20131216_225545_730408_6F55D1CD) Subject: Re: [PATCH 2/3] mac80211: reset TSF to 0 when joining a mesh To: Thomas Pedersen Cc: Johannes Berg , open80211s , linux-wireless , Thomas Pedersen Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-wireless-owner@vger.kernel.org List-ID: 2013/12/16 Thomas Pedersen : > On Mon, Dec 16, 2013 at 4:33 AM, Sergey Ryazanov wrote: >> Hello Thomas, >> >> 2013/12/16 Thomas Pedersen : >>> diff --git a/net/mac80211/mesh.c b/net/mac80211/mesh.c >>> index 330d1f7..1174157 100644 >>> --- a/net/mac80211/mesh.c >>> +++ b/net/mac80211/mesh.c >>> @@ -802,6 +802,8 @@ int ieee80211_start_mesh(struct ieee80211_sub_if_data *sdata) >>> return -ENOMEM; >>> } >>> >>> + /* next beacon will be DTIM-1, so TSF=0 was DTIM=0 */ >>> + drv_set_tsf(local, sdata, 0); >>> ieee80211_bss_info_change_notify(sdata, changed); >>> >>> netif_carrier_on(sdata->dev); >> >> What happen with AP interface on the same radio if we configure mesh >> portal? Clients could be confused by such TSF jump. > > Like Johannes said; either the driver supports per-vif TSF, or well, > it doesn't. Anyway wouldn't clients reset their own TSF when the new > beacon is received? > Yeah, IEEE 802.11 says that stations must blindly use AP time, but it says nothing about the situation when time is accidentally reset to zero. I can't predict reaction of each chip/firmware/driver to such situation. Another one unclear situation is the reaction of peers of mesh STA, which share the same radio (and same TSF). If we silently reset its time, what happens to the time synchronization with neighbors? Why could not we calculate DTIM counter value on basis of known TSF and Beacon/DTIM interval, instead of primitive time reset? -- BR, Sergey