netdev - Re: [PATCH net V2 1/2] tun: unbreak truncated packet signalling

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Date:	Wed, 11 Dec 2013 11:28:13 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>,
	Vlad Yasevich <vyasevich@...il.com>
Subject: Re: [PATCH net V2 1/2] tun: unbreak truncated packet signalling

On 12/10/2013 11:32 PM, Michael S. Tsirkin wrote:
> On Tue, Dec 10, 2013 at 01:49:45PM +0800, Jason Wang wrote:
>> > Commit 6680ec68eff47d36f67b4351bc9836fd6cba9532
>> > (tuntap: hardware vlan tx support) breaks the truncated packet signal by nev
>> > return a length greater than iov length in tun_put_user(). This patch fixes
>> > by always return the length of packet plus possible vlan header. Caller can
>> > detect the truncated packet by comparing the return value and the size of io
>> > length.
>> > 
>> > Cc: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
>> > Cc: Michael S. Tsirkin <mst@...hat.com>
>> > Signed-off-by: Vlad Yasevich <vyasevich@...il.com>
>> > Signed-off-by: Jason Wang <jasowang@...hat.com>
>> > ---
>> > Changes from v1:
>> > - increase total unconditionally
>> > - do not move veth structure out of the vlan handing block
>> > ---
>> >  drivers/net/tun.c | 16 +++++++++-------
>> >  1 file changed, 9 insertions(+), 7 deletions(-)
>> > 
>> > diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>> > index e26cbea..cd142134 100644
>> > --- a/drivers/net/tun.c
>> > +++ b/drivers/net/tun.c
>> > @@ -1184,7 +1184,7 @@ static ssize_t tun_put_user(struct tun_struct *tun,
>> >  {
>> >  	struct tun_pi pi = { 0, skb->protocol };
>> >  	ssize_t total = 0;
>> > -	int vlan_offset = 0;
>> > +	int vlan_offset = 0, offset;
>> >  
>> >  	if (!(tun->flags & TUN_NO_PI)) {
>> >  		if ((len -= sizeof(pi)) < 0)
>> > @@ -1248,6 +1248,8 @@ static ssize_t tun_put_user(struct tun_struct *tun,
>> >  		total += tun->vnet_hdr_sz;
>> >  	}
>> >  
>> > +	offset = total;
>> > +	total += skb->len;
>> >  	if (!vlan_tx_tag_present(skb)) {
>> >  		len = min_t(int, skb->len, len);
>> >  	} else {
>> > @@ -1262,24 +1264,24 @@ static ssize_t tun_put_user(struct tun_struct *tun,
>> >  
>> >  		vlan_offset = offsetof(struct vlan_ethhdr, h_vlan_proto);
>> >  		len = min_t(int, skb->len + VLAN_HLEN, len);
>> > +		total += VLAN_HLEN;
>> >  
>> >  		copy = min_t(int, vlan_offset, len);
>> > -		ret = skb_copy_datagram_const_iovec(skb, 0, iv, total, copy);
>> > +		ret = skb_copy_datagram_const_iovec(skb, 0, iv, offset, copy);
>> >  		len -= copy;
>> > -		total += copy;
>> > +		offset += copy;
>> >  		if (ret || !len)
>> >  			goto done;
>> >  
>> >  		copy = min_t(int, sizeof(veth), len);
>> > -		ret = memcpy_toiovecend(iv, (void *)&veth, total, copy);
>> > +		ret = memcpy_toiovecend(iv, (void *)&veth, offset, copy);
>> >  		len -= copy;
>> > -		total += copy;
>> > +		offset += copy;
>> >  		if (ret || !len)
>> >  			goto done;
>> >  	}
>> >  
>> > -	skb_copy_datagram_const_iovec(skb, vlan_offset, iv, total, len);
>> > -	total += len;
>> > +	skb_copy_datagram_const_iovec(skb, vlan_offset, iv, offset, len);
>> >  
>> >  done:
>> >  	tun->dev->stats.tx_packets++;
> offset is not descriptive. I would call new variable "copied",
> and change all code to use that, do
> total = copied + skb->len, total is then the total length.
>

Ok, will do it in v3.
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