netdev - RE: [PATCH v13 10/16] Add a hook to intercept external buffers from NIC driver.

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Date:	Wed, 27 Oct 2010 09:33:12 +0800
From:	"Xin, Xiaohui" <xiaohui.xin@...el.com>
To:	David Miller <davem@...emloft.net>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mst@...hat.com" <mst@...hat.com>, "mingo@...e.hu" <mingo@...e.hu>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"jdike@...ux.intel.com" <jdike@...ux.intel.com>
Subject: RE: [PATCH v13 10/16] Add a hook to intercept external buffers from
 NIC driver.

>-----Original Message-----
>From: David Miller [mailto:davem@...emloft.net]
>Sent: Tuesday, October 19, 2010 11:24 PM
>To: Xin, Xiaohui
>Cc: netdev@...r.kernel.org; kvm@...r.kernel.org; linux-kernel@...r.kernel.org;
>mst@...hat.com; mingo@...e.hu; herbert@...dor.apana.org.au; jdike@...ux.intel.com
>Subject: Re: [PATCH v13 10/16] Add a hook to intercept external buffers from NIC driver.
>
>From: xiaohui.xin@...el.com
>Date: Fri, 15 Oct 2010 17:12:11 +0800
>
>> @@ -2891,6 +2922,11 @@ static int __netif_receive_skb(struct sk_buff *skb)
>>  ncls:
>>  #endif
>>
>> +	/* To intercept mediate passthru(zero-copy) packets here */
>> +	skb = handle_mpassthru(skb, &pt_prev, &ret, orig_dev);
>> +	if (!skb)
>> +		goto out;
>> +
>>  	/* Handle special case of bridge or macvlan */
>>  	rx_handler = rcu_dereference(skb->dev->rx_handler);
>>  	if (rx_handler) {
>
>If you consume the packet here, devices in passthru mode cannot
>be use with bonding.
>
>But there is nothing that prevents a bond being created with such
>a device.
>
>So we have to either prevent such configurations (bad) or make
>it work somehow (good) :-)

The big picture may like this:
To prevent such configurations, we should add code to check in both
mp and bonding driver. If a nic is in zero-copy mode , bonding can't
be made with it, and if nic is in bonding mode, we can't bind the device
to do zero-copy.

If we want to support such configurations, it also has some constraints.
If bonding is created first, we need code to check if all the slaves support
zero-copy mode, and if yes, all the slaves should be assigned a same 
page_ctor(), all the packets received should be intercepted with master nic. 
If not, fails.
If zero-copy is enabled first, bonding created with it should fail.

Somehow, it seems not a trivial work to support it now. Can we support it
later and as a todo with our current work?

Thanks
Xiaohui




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