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

[Stephen Hemminger <stephen.hemminger@vyatta.com>]

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

Maybe the problem is specific to a ethernet driver. Some devices poll
for link changes, and also do a manual check when ioctl was done.
This was mostly typical of older hardware that did not have a PHY
interrupt.