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Message-ID: <20130128101111.GB5337@redhat.com>
Date: Mon, 28 Jan 2013 12:11:11 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: Toralf Förster <toralf.foerster@....de>,
netdev@...r.kernel.org,
Linux Kernel <linux-kernel@...r.kernel.org>,
David Miller <davem@...emloft.net>
Subject: [PATCH] tun: fix carrier on/off status
Commit c8d68e6be1c3b242f1c598595830890b65cea64a removed carrier off call
from tun_detach since it's now called on queue disable and not only on
tun close. This confuses userspace which used this flag to detect a
free tun. To fix, move on/off calls to setiff/close respectively.
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
On Mon, Jan 28, 2013 at 05:38:24PM +0800, Jason Wang wrote:
> On Saturday, January 26, 2013 11:29:49 AM Toralf Förster wrote:
> > Re: How to find an unused TAP device with kernel 3.8 ?
> > 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<UP,BROADCAST,PROMISC,MULTICAST> mtu 1500
> >
> > > br0: flags=4419<UP,BROADCAST,RUNNING,PROMISC,MULTICAST> mtu 1500
> >
> > < tap0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
> >
> > > tap0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> 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.
This will set carrier off if all queues are disabled, which I think is a
problem as it would confuse the script. How about the following instead:
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index af372d0..00dfdad 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1644,10 +1644,10 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
device_create_file(&tun->dev->dev, &dev_attr_owner) ||
device_create_file(&tun->dev->dev, &dev_attr_group))
pr_err("Failed to create tun sysfs files\n");
-
- netif_carrier_on(tun->dev);
}
+ netif_carrier_on(tun->dev);
+
tun_debug(KERN_INFO, tun, "tun_set_iff\n");
if (ifr->ifr_flags & IFF_NO_PI)
@@ -2124,6 +2124,8 @@ static int tun_chr_close(struct inode *inode, struct file *file)
struct tun_file *tfile = file->private_data;
struct net *net = tfile->net;
+ netif_carrier_off(tun->dev);
+
tun_detach(tfile, true);
put_net(net);
--
MST
--
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