netdev - Re: [PATCH] netns: keep vlan slaves on master netns move

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Message-ID: <20100917132219.GA2363813@jupiter.n2.diac24.net>
Date:	Fri, 17 Sep 2010 15:22:19 +0200
From:	David Lamparter <equinox@...c24.net>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Daniel Lezcano <daniel.lezcano@...e.fr>,
	David Lamparter <equinox@...c24.net>
Subject: Re: [PATCH] netns: keep vlan slaves on master netns move

previously, if a vlan master device was moved from one network namespace
to another, all 802.1q and macvlan slaves were deleted.

we can use dev->reg_state to figure out whether dev_change_net_namespace
is happening, since that won't set dev->reg_state NETREG_UNREGISTERING.
so, this changes 8021q and macvlan to ignore NETDEV_UNREGISTER when
reg_state is not NETREG_UNREGISTERING.

Signed-off-by: David Lamparter <equinox@...c24.net>
Reviewed-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Acked-by: Daniel Lezcano <daniel.lezcano@...e.fr>
Acked-by: Patrick McHardy <kaber@...sh.net>
---
Hi David,

Q)ueue, F)eedback, A)pply?

-David

On Tue, Sep 14, 2010 at 07:10:01PM -0700, Eric W. Biederman wrote:
> Reviewed-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> 
> My inclination is that the best way to handle this is to would be to
> push the device deletion for vlan and macvlan devices into the device
> core, where we could get the advantage of batched deletions.  Right
> now vlan and macvlan devices are the only devices I know of that cause
> other devices to be removed during unregister, so removing that
> specialness seems reasonable.
> 
> However not being able to move the primary vlan to a different network
> namespace is usability bug with no real alternatives.  There are
> not any other patches on the table right now, and your patch below
> seems obviously correct.  Let's get this merged before we forget about
> this, bug fix.
> 
> David Lamparter <equinox@...c24.net> writes:
> > On Tue, Aug 24, 2010 at 01:50:56PM +0200, David Lamparter wrote:
> >> attached patch makes it possible to keep macvlan / 802.1q slave devices
> >> on moving their master to a different namespace. as the opposite works
> >> without problems (moving the slaves into a different namespace), this
> >> shouldn't cause problems either.
> >
> > I would like to resurrect this. After the small excursion into
> > NETREG_NETNS_MOVING i've reevaluated my personal opinion and think the
> > behaviour is the desired one and this patch is the cleanest way to
> > implement it. While it depends on somewhat "fine print" on the reg_state
> > state machine, the probability of major screw-ups in this region is
> > rather small and it also quite likely makes a nice large boom when it is
> > unduly tampered with.

 drivers/net/macvlan.c |    4 ++++
 net/8021q/vlan.c      |    4 ++++
 net/core/dev.c        |    4 ++++
 3 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index f15fe2c..f43f8e4 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -754,6 +754,10 @@ static int macvlan_device_event(struct notifier_block *unused,
 		}
 		break;
 	case NETDEV_UNREGISTER:
+		/* twiddle thumbs on netns device moves */
+		if (dev->reg_state != NETREG_UNREGISTERING)
+			break;
+
 		list_for_each_entry_safe(vlan, next, &port->vlans, list)
 			vlan->dev->rtnl_link_ops->dellink(vlan->dev, NULL);
 		break;
diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index 3c1c8c1..cdc37e8 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -516,6 +516,10 @@ static int vlan_device_event(struct notifier_block *unused, unsigned long event,
 		break;
 
 	case NETDEV_UNREGISTER:
+		/* twiddle thumbs on netns device moves */
+		if (dev->reg_state != NETREG_UNREGISTERING)
+			break;
+
 		/* Delete all VLANs for this dev. */
 		grp->killall = 1;
 
diff --git a/net/core/dev.c b/net/core/dev.c
index 1f466e8..b1589bc 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5618,6 +5618,10 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
 
 	/* Notify protocols, that we are about to destroy
 	   this device. They should clean all the things.
+
+	   Note that dev->reg_state stays at NETREG_REGISTERED.
+	   This is wanted because this way 8021q and macvlan know
+	   the device is just moving and can keep their slaves up.
 	*/
 	call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
 	call_netdevice_notifiers(NETDEV_UNREGISTER_BATCH, dev);
--
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