RE: [PATCH net-next] hv_netvsc: Increase delay for RNDIS_STATUS_NETWORK_CHANGE

[Haiyang Zhang]

> -----Original Message-----
> From: David Miller [mailto:davem@xxxxxxxxxxxxx]
> Sent: Tuesday, February 9, 2016 5:05 AM
> To: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx; KY Srinivasan <kys@xxxxxxxxxxxxx>;
> olaf@xxxxxxxxx; vkuznets@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> driverdev-devel@xxxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH net-next] hv_netvsc: Increase delay for
> RNDIS_STATUS_NETWORK_CHANGE
> 
> From: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> Date: Tue,  2 Feb 2016 16:15:56 -0800
> 
> > We simulates a link down period for RNDIS_STATUS_NETWORK_CHANGE
> > message to trigger DHCP renew. User daemons may need multiple seconds
> > to trigger the link down event. (e.g. ifplugd: 5sec, network-manager:
> > 4sec.) So update this link down period to 10 sec to properly trigger DHCP
> renew.
> >
> > Signed-off-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> 
> Two things look really bad about this to me:
> 
> 1) Any value you choose is arbitrary.  If some new network configuration
> daemon
>    is slower, you will have to change this value again.
> 
>    This is _NOT_ sustainable in the long term.
> 
> 2) It is completely unclear to me why this driver needs to delay at all or
>    wait for anything.  I see no other driver having to deal with this issue.
> 
> Until you address both of these points I am not going to apply this patch.

1) I share your concern as well. Is there a universal way to immediately trigger 
DHCP renew of all current and future daemons with a single event from kernel? 
If not, can we put the delay (RNDIS_STATUS_NETWORK_CHANGE only) into a 
tunable variable of this driver?

2) We used to have the call_usermodehelper "/etc/init.d/network restart" to 
trigger DHCP renew. In commit 27a70af3f4, Vitaly has replaced it with the current 
code that updates the link status with at least 2 seconds interval, so that the 
"link_watch infrastructure" can send notification out. link_watch infrastructure 
only sends one notification per second.

Thanks,
- Haiyang