netdev - Re: Question about VLAN + checksum offloading

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Date:	Mon, 19 May 2008 19:45:24 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
CC:	Ichiro Suzuki <isuzuki@...aclelinux.com>, netdev@...r.kernel.org,
	Naohiro Ooiwa <nooiwa@...aclelinux.com>
Subject: Re: Question about VLAN + checksum offloading

Patrick McHardy wrote:
> Waskiewicz Jr, Peter P wrote:
>>> o If so, is there any mechanism to propagate  real_dev->features 
>>> flags in vlan.c?
>>
>> There isn't an explicit way.  I had written patches into e1000, igb,
>> e1000e, and ixgbe to propogate the VLAN flags within the driver when the
>> VLAN device was created.  The trick though is if you remove a feature
>> flag with ethtool, say checksum offload, on your main device, you
>> probably should turn it off on your VLAN devices.  Patrick McHardy
>> pointed me at netdev_feature_change() to use within the driver.  I'll
>> admit I haven't had the time to fix my drivers to use this call, but it
>> certainly looks like the way to go.  Please see the (middle) of the
>> thread here: http://marc.info/?l=linux-netdev&m=120878809806631&w=2
>>
>>> o If such mechanism doesn't exist, is my patch reasonable?
>>
>> I would say yes, halfway.  The issue is you probably want to remove the
>> feature flag from the VLAN device if you removed the flag from the
>> parent device as well.
> 
> 
> Yes, it should use the same mechanism as suggested for the
> VLAN accel feature. And it should be limited to features

I meant TSO, sorry.

> that are known to work, not just blindly copy everything.
> 
> I will be catching up with the VLAN patches posted recently
> sometime next week. I guess I can then also add a patch for
> feature propagation myself if you don't beat me to it :)
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