Subject: Re: [net-next 1/5] macvtap: set transport header before passing skb to lower device

From: Jason Wang <[email-masked]>
Date: Wed, 27 Mar 2013 11:12:38 +0800

On 03/26/2013 11:06 PM, Eric Dumazet wrote:
> On Tue, 2013-03-26 at 14:19 +0800, Jason Wang wrote:
>> Set the transport header for 1) some drivers (e.g ixgbe) needs l4 header 2)
>> precise packet length estimation (introduced in 1def9238) needs l4 header to
>> compute header length.
>>
>> For the packets with partial checksum, the patch just set the transport header
>> to csum_start. Otherwise tries to use skb_flow_dissect() to get l4 offset, if it
>> fails, just pretend no l4 header.
>>
>> Cc: Eric Dumazet <[email-masked]>
>> Signed-off-by: Jason Wang <[email-masked]>
>> ---
>>  drivers/net/macvtap.c |    9 +++++++++
>>  1 files changed, 9 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
>> index a449439..acf6450 100644
>> --- a/drivers/net/macvtap.c
>> +++ b/drivers/net/macvtap.c
>> @@ -21,6 +21,7 @@
>>  #include <net/rtnetlink.h>
>>  #include <net/sock.h>
>>  #include <linux/virtio_net.h>
>> +#include <net/flow_keys.h>
>>  
>>  /*
>>   * A macvtap queue is the central object of this driver, it connects
>> @@ -645,6 +646,7 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
>>  	int vnet_hdr_len = 0;
>>  	int copylen = 0;
>>  	bool zerocopy = false;
>> +	struct flow_keys keys;
>>  
>>  	if (q->flags & IFF_VNET_HDR) {
>>  		vnet_hdr_len = q->vnet_hdr_sz;
>> @@ -725,6 +727,13 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
>>  			goto err_kfree;
>>  	}
>>  
>> +	if (skb->ip_summed == CHECKSUM_PARTIAL)
> where ip_summed is set to this value ?
>
>> +		skb_set_transport_header(skb, skb_checksum_start_offset(skb));
>> +	else if (skb_flow_dissect(skb, &keys))
>> +		skb_set_transport_header(skb, keys.thoff);
>> +	else
>> +		skb_set_transport_header(skb, ETH_HLEN);
>> +
>>  	rcu_read_lock_bh();
>>  	vlan = rcu_dereference_bh(q->vlan);
>>  	/* copy skb_ubuf_info for callback when skb has no error */
> This driver has nice helpers.

Yes, skb_set_partial_csum()
> You should add this code in a helper as well.

Ok
> Because its not clear at this point if csum_start/csum_offset/ip_summed
> are consistent.

Since David has applied the seires, will send patches on top.

Thanks
>
>
>
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