Re: [PATCH net-next ] Fix time-lag of IFF_RUNNING flag consistency between vlan and real devices

Le dimanche 28 août 2011 à 22:20 +0900, HAYASAKA Mitsuo a écrit :

Hi Stephen and Herbert

Thank you for your comments.

(2011/08/26 15:08), Stephen Hemminger wrote:

quoted

I don't think this is the right way to solve the problem.

The flags are supposed to propagate back from real device to vlan
via network notifications.

Just doing this for ioctl is not enough, API's other than user space depend on this.
Also the user may have manually set different flags on vlan than on
the real device.

I agreed.
I will try another way to solve this problem, as you said.


(2011/08/26 15:45), Herbert Xu wrote:

quoted

On Thu, Aug 25, 2011 at 11:08:59PM -0700, Stephen Hemminger wrote:

quoted

Just doing this for ioctl is not enough, API's other than user space depend on this.
Also the user may have manually set different flags on vlan than on
the real device.

Right, anything that tests netif_carrier_ok directly on the VLAN
device will still be delayed.

Now I remember discussing this issue in Japan.  However, I can't
recall the exact scenario in which the delay occured.

Is the issue with the link status going down on the real device,
or the real device coming up?

IIRC we already have mechanisms in place to ensure that down events
are not delayed by linkwatch.  Of course it is possible that this
isn't working for some reason, or some other part of the system is
causing the delay.

So please clarify the scenario for us Hayasaka-san.  Also please
let us know how you measured the delay.

Thanks,

This issue happens when the link status is going down on the real 
device.

ex) A cable is broken, or is unplugged from a NIC.

I measured the delay using ioctl with SIOCGIFFLAGS from userspace 
in order to check if there is a time-lag of the flag between vlan 
and real devices.

Also, you can check it using a script below.

-------------------------
#!/bin/sh
t=0
while :
do
	echo $t; t=$((t+1))
	echo -n real; ifconfig RealDev | grep UP
	echo -n vlan; ifconfig VlanDev | grep UP
	sleep 0.2
done
-------------------------

The result is shown as follows.
It is observed that there is a time-lag of RUNNING status between 
real and vlan devices.

Hi !

This reminds me some work done in linkwatch

Please take a look at commit e014debecd3ee3832e647 (linkwatch:
linkwatch_forget_dev() to speedup device dismantle)

And more generally, code in net/core/link_watch.c