From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755477Ab3A1Jin (ORCPT ); Mon, 28 Jan 2013 04:38:43 -0500 Received: from mx1.redhat.com ([209.132.183.28]:27595 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755151Ab3A1Jih convert rfc822-to-8bit (ORCPT ); Mon, 28 Jan 2013 04:38:37 -0500 From: Jason Wang To: Toralf =?ISO-8859-1?Q?F=F6rster?= Cc: netdev@vger.kernel.org, Linux Kernel Subject: Re: How to find an unused TAP device with kernel 3.8 ? Date: Mon, 28 Jan 2013 17:38:24 +0800 Message-ID: <3592886.xagLc7Uij9@jason-thinkpad-t430s> User-Agent: KMail/4.9.4 (Linux/3.7.0-rc7+; KDE/4.9.4; x86_64; ; ) In-Reply-To: <5103B01D.5070303@gmx.de> References: <5103B01D.5070303@gmx.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="iso-8859-1" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Saturday, January 26, 2013 11:29:49 AM Toralf Förster wrote: > With kernel 3.8. I just realized that all pre-defined TAP devices are > RUNNING even if no virtual linux system is using it. Now I'm wondering > whether this is a new feature of the upcoming kernel, a bug of the old - > and how I can avoid that. > > Background : When I start a user mode linux instance, I currently grep > for the next free tap device in this way : > > Code: > for t in $(ifconfig | grep "^tap" | cut -f1 -d:) > do > ethtool $t | grep -q 'Link detected: no' > if [[ $? -eq 0 ]]; then > NET="tuntap,$t" > break > fi > done > > but this doesn't work now anymore. > > Here is the diff in dmesg > > $ diff 3.7.1 3.8.0-rc1+ | grep UP > > < br0: flags=4355 mtu 1500 > > > br0: flags=4419 mtu 1500 > > < tap0: flags=4099 mtu 1500 > > > tap0: flags=4163 mtu 1500 > > more details : http://forums.gentoo.org/viewtopic-p-7211498.html#7211498 Looks like something wrong with the carrier detection of tap. Please try the following patch to see if it helps. Thanks. diff --git a/drivers/net/tun.c b/drivers/net/tun.c index cc09b67..d8a53c3 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -438,6 +438,9 @@ static void __tun_detach(struct tun_file *tfile, bool clean) sock_put(&tfile->sk); } + if (tun && tun->numqueues == 0) + netif_carrier_off(tun->dev); + if (clean) { if (tun && tun->numqueues == 0 && tun->numdisabled == 0 && !(tun->flags & TUN_PERSIST)) @@ -473,6 +476,7 @@ static void tun_detach_all(struct net_device *dev) BUG_ON(tun->numqueues != 0); synchronize_net(); + netif_carrier_off(dev); for (i = 0; i < n; i++) { tfile = rtnl_dereference(tun->tfiles[i]); /* Drop read queue */ @@ -531,6 +535,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file) sock_hold(&tfile->sk); tun_set_real_num_queues(tun); + netif_carrier_on(tun->dev); /* device is allowed to go away first, so no need to hold extra * refcnt. -- 1.7.1