Subject: Re: [PATCH 4/4] lguest: Use GSO/IFF_VNET_HDR extensions on tun/tap

From: Max Krasnyansky <[email-masked]>
Date: Tue, 01 Jul 2008 22:25:04 -0700

Rusty Russell wrote:
> On Thursday 26 June 2008 05:07:18 Anthony Liguori wrote:
>> Rusty Russell wrote:
>>> @@ -1563,6 +1561,16 @@ static void setup_tun_net(char *arg)
>>>  	/* Tell Guest what MAC address to use. */
>>>  	add_feature(dev, VIRTIO_NET_F_MAC);
>>>  	add_feature(dev, VIRTIO_F_NOTIFY_ON_EMPTY);
>>> +	/* Expect Guest to handle everything except UFO */
>>> +	add_feature(dev, VIRTIO_NET_F_CSUM);
>> You're setting this feature twice.
> 
> Hmm, not in the version here?
> 
>>> +	add_feature(dev, VIRTIO_NET_F_GUEST_CSUM);
>> You set this feature, but I never see the virtio-net driver acknowledge
>> the feature.  Curiously, my implementation with KVM is struggling
>> because UDP packet checksums are not correct so the DHCP client is
>> ignoring them.  If I disable CSUM offload, things it works fine (using
>> the virtio-net header).  The problem is only host=>guest, guest=>host is
>> fine.
> 
> OK, found this: wrong args to skb_partial_csum_set.  It was found by Mark 
> McLoughlin before, I just lost the fix when I extracted this into a separate 
> patch.  I chose to move the call to skb_partial_csum_set(), rather than use 
> his fix (which assumed a tap not tun device).
> 
> Here's two fixes on top of previous patch:
> 
> diff -u b/drivers/net/tun.c b/drivers/net/tun.c
> --- b/drivers/net/tun.c	Thu Jun 26 00:21:59 2008 +1000
> +++ b/drivers/net/tun.c	Thu Jun 26 14:35:03 2008 +1000
> @@ -298,11 +298,11 @@
>  		if ((len -= sizeof(gso)) > count)
>  			return -EINVAL;
>  
> -		if (gso.hdr_len > len)
> -			return -EINVAL;
> -
>  		if (memcpy_fromiovec((void *)&gso, iv, sizeof(gso)))
>  			return -EFAULT;
> +
> +		if (gso.hdr_len > len)
> +			return -EINVAL;
>  	}

Yep, looks better now.

>  
>  	if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) {
> @@ -324,6 +324,16 @@
>  		return -EFAULT;
>  	}
>  
> +	if (gso.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
> +		if (!skb_partial_csum_set(skb, gso.csum_start,
> +					  gso.csum_offset)) {
> +			tun->dev->stats.rx_dropped++;
> +			kfree_skb(skb);
> +			return -EINVAL;
> +		}
> +	} else if (tun->flags & TUN_NOCHECKSUM)
> +		skb->ip_summed = CHECKSUM_UNNECESSARY;
> +
>  	switch (tun->flags & TUN_TYPE_MASK) {
>  	case TUN_TUN_DEV:
>  		skb_reset_mac_header(skb);
> @@ -335,16 +345,6 @@
>  		break;
>  	};
>  
> -	if (gso.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
> -		if (!skb_partial_csum_set(skb, gso.csum_start,
> -					  gso.csum_offset)) {
> -			tun->dev->stats.rx_dropped++;
> -			kfree_skb(skb);
> -			return -EINVAL;
> -		}
> -	} else if (tun->flags & TUN_NOCHECKSUM)
> -		skb->ip_summed = CHECKSUM_UNNECESSARY;
> -
>  	if (gso.gso_type != VIRTIO_NET_HDR_GSO_NONE) {
>  		pr_debug("GSO!\n");
>  		switch (gso.gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {

Do you want to resent the GSO patch with all the latest fixes ? ie other
things (stat counters) I pointed out in the prev email.
I'll ack it.

Thanx
Max