[v13,10/16] Add a hook to intercept external buffers from NIC driver.

From: Xin Xiaohui <xiaohui.xin@intel.com>

The hook is called in __netif_receive_skb().

Signed-off-by: Xin Xiaohui <xiaohui.xin@intel.com>
Signed-off-by: Zhao Yu <yzhao81new@gmail.com>
Reviewed-by: Jeff Dike <jdike@linux.intel.com>
---
 net/core/dev.c |   37 +++++++++++++++++++++++++++++++++++++
 1 files changed, 37 insertions(+), 0 deletions(-)

From: xiaohui.xin@intel.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) :-)
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>-----Original Message-----
>From: David Miller [mailto:davem@davemloft.net]
>Sent: Tuesday, October 19, 2010 11:24 PM
>To: Xin, Xiaohui
>Cc: netdev@vger.kernel.org; kvm@vger.kernel.org; linux-kernel@vger.kernel.org;
>mst@redhat.com; mingo@elte.hu; herbert@gondor.apana.org.au; jdike@linux.intel.com
>Subject: Re: [PATCH v13 10/16] Add a hook to intercept external buffers from NIC driver.
>
>From: xiaohui.xin@intel.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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From: "Xin, Xiaohui" <xiaohui.xin@intel.com>
Date: Wed, 27 Oct 2010 09:33:12 +0800

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

I would prefer the feature work properly, rather than only in specific
cases, before being integated.
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I have addressed this issue in v14 patch set.

Thanks
Xiaohui

>-----Original Message-----
>From: David Miller [mailto:davem@davemloft.net]
>Sent: Saturday, October 30, 2010 4:29 AM
>To: Xin, Xiaohui
>Cc: netdev@vger.kernel.org; kvm@vger.kernel.org; linux-kernel@vger.kernel.org;
>mst@redhat.com; mingo@elte.hu; herbert@gondor.apana.org.au; jdike@linux.intel.com
>Subject: Re: [PATCH v13 10/16] Add a hook to intercept external buffers from NIC driver.
>
>From: "Xin, Xiaohui" <xiaohui.xin@intel.com>
>Date: Wed, 27 Oct 2010 09:33:12 +0800
>
>> Somehow, it seems not a trivial work to support it now. Can we support it
>> later and as a todo with our current work?
>
>I would prefer the feature work properly, rather than only in specific
>cases, before being integated.
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