Date:	Wed, 27 Jan 2010 09:42:37 -0800
From:	Sridhar Samudrala <sri@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	David Miller <davem@...emloft.net>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next-2.6] packet: Add GSO/checksum offload support
 to af_packet sockets

On Wed, 2010-01-27 at 13:42 +0200, Michael S. Tsirkin wrote: 
> On Tue, Jan 26, 2010 at 12:30:19PM -0800, Sridhar Samudrala wrote:
> > This patch adds GSO/checksum offload to af_packet sockets using
> > virtio_net_hdr. Based on Rusty's patch to add this support to tun.
> > It allows GSO/checksum offload to be enabled when using raw socket
> > backend with virtio_net.
> > Adds PACKET_VNET_HDR socket option to prepend virtio_net_hdr in the
> > receive path and process/skip virtio_net_hdr in the send path. This
> > option is only allowed with SOCK_RAW sockets attached to ethernet
> > type devices.
> > 
> > Signed-off-by: Sridhar Samudrala <sri@...ibm.com>
> 
> So the main issue with this implemenation is that it silently fails for
> non-ethernet protocols.  It would be better to detect unsupported
> protocols and return an error to user. 

Yes. I could return EINVAL or EOPNOTSUPP when trying to send/receive a
packet with virtio_net_hdr on non-ethernet devices.

> This is same issue that was
> pointed out by DaveM with my earlier attempt to solve a different
> (related) problem:
> http://lkml.org/lkml/2010/1/5/474
> For an incomplete prototype attempting to solve the issue in a generic way:
> http://lkml.org/lkml/2010/1/6/56
> 
> A couple of additional comments below.
> 
> > diff --git a/include/linux/if_packet.h b/include/linux/if_packet.h
> > index 4021d47..aa57a5f 100644
> > --- a/include/linux/if_packet.h
> > +++ b/include/linux/if_packet.h
> > @@ -46,6 +46,7 @@ struct sockaddr_ll {
> >  #define PACKET_RESERVE			12
> >  #define PACKET_TX_RING			13
> >  #define PACKET_LOSS			14
> > +#define PACKET_VNET_HDR			15
> >  
> >  struct tpacket_stats {
> >  	unsigned int	tp_packets;
> > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> > index 53633c5..36d5360 100644
> > --- a/net/packet/af_packet.c
> > +++ b/net/packet/af_packet.c
> > @@ -80,6 +80,8 @@
> >  #include <linux/init.h>
> >  #include <linux/mutex.h>
> >  #include <linux/if_vlan.h>
> > +#include <linux/virtio_net.h>
> > +#include <linux/if_arp.h>
> >  
> >  #ifdef CONFIG_INET
> >  #include <net/inet_common.h>
> > @@ -193,7 +195,8 @@ struct packet_sock {
> >  	struct mutex		pg_vec_lock;
> >  	unsigned int		running:1,	/* prot_hook is attached*/
> >  				auxdata:1,
> > -				origdev:1;
> > +				origdev:1,
> > +				vnet_hdr:1;
> >  	int			ifindex;	/* bound device		*/
> >  	__be16			num;
> >  	struct packet_mclist	*mclist;
> > @@ -1056,6 +1059,30 @@ out:
> >  }
> >  #endif
> >  
> > +static inline struct sk_buff *packet_alloc_skb(struct sock *sk, size_t prepad,
> > +					       size_t reserve, size_t len,
> > +					       size_t linear, int noblock,
> > +					       int *err)
> > +{
> > +	struct sk_buff *skb;
> > +
> > +	/* Under a page?  Don't bother with paged skb. */
> > +	if (prepad + len < PAGE_SIZE || !linear)
> > +		linear = len;
> > +
> > +	skb = sock_alloc_send_pskb(sk, prepad + linear, len - linear, noblock,
> > +				   err);
> > +	if (!skb)
> > +		return NULL;
> > +
> > +	skb_reserve(skb, reserve);
> > +	skb_put(skb, linear);
> > +	skb->data_len = len - linear;
> > +	skb->len += len - linear;
> > +
> > +	return skb;
> > +}
> > +
> >  static int packet_snd(struct socket *sock,
> >  			  struct msghdr *msg, size_t len)
> >  {
> > @@ -1066,14 +1093,15 @@ static int packet_snd(struct socket *sock,
> >  	__be16 proto;
> >  	unsigned char *addr;
> >  	int ifindex, err, reserve = 0;
> > +	struct virtio_net_hdr vnethdr = { 0 };
> > +	int offset = 0;
> > +	struct packet_sock *po = pkt_sk(sk);
> >  
> >  	/*
> >  	 *	Get and verify the address.
> >  	 */
> >  
> >  	if (saddr == NULL) {
> > -		struct packet_sock *po = pkt_sk(sk);
> > -
> >  		ifindex	= po->ifindex;
> >  		proto	= po->num;
> >  		addr	= NULL;
> > @@ -1100,25 +1128,52 @@ static int packet_snd(struct socket *sock,
> >  	if (!(dev->flags & IFF_UP))
> >  		goto out_unlock;
> >  
> > -	err = -EMSGSIZE;
> > -	if (len > dev->mtu+reserve)
> > -		goto out_unlock;
> > +	if (po->vnet_hdr) {
> > +		err = -EINVAL;
> > +		if (dev->type != ARPHRD_ETHER)
> > +			goto out_unlock;
> > +
> > +		if (len < sizeof(vnethdr))
> > +			goto out_unlock;
> >  
> > -	skb = sock_alloc_send_skb(sk, len + LL_ALLOCATED_SPACE(dev),
> > -				msg->msg_flags & MSG_DONTWAIT, &err);
> > +		len -= sizeof(vnethdr);
> > +
> > +		err = -EFAULT;
> > +		if (memcpy_fromiovec((void *)&vnethdr, msg->msg_iov,
> > +					sizeof(vnethdr))) 
> > +			goto out_unlock;
> > +	
> > +		if ((vnethdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
> > +		    (vnethdr.csum_start + vnethdr.csum_offset + 2 >
> > +		      vnethdr.hdr_len))
> > +			vnethdr.hdr_len = vnethdr.csum_start +
> > +						 vnethdr.csum_offset + 2;
> > +
> > +		err = -EINVAL;
> > +		if (vnethdr.hdr_len > len)
> > +			goto out_unlock;
> > +	} else {
> > +		err = -EMSGSIZE;
> > +		if (len > dev->mtu+reserve)
> > +			goto out_unlock;
> 
> IMO we should always perform the length check if GSO is off.
OK. I will fix this. 
> 
> > +	}
> > +
> > +	err = -ENOBUFS;
> > +	skb = packet_alloc_skb(sk, LL_ALLOCATED_SPACE(dev),
> > +			       LL_RESERVED_SPACE(dev), len, vnethdr.hdr_len,
> > +			       msg->msg_flags & MSG_DONTWAIT, &err);
> >  	if (skb == NULL)
> >  		goto out_unlock;
> >  
> > -	skb_reserve(skb, LL_RESERVED_SPACE(dev));
> > -	skb_reset_network_header(skb);
> > +	skb_set_network_header(skb, reserve);
> 
> I think the above is wrong for vlans?

I also thought we need to address vlans here, but even tun doesn't
handle this in the send routine. I submitted a patch that fixed
skb_gso_segment() to handle vlan packets. This will address both
tun and packet sockets.
http://thread.gmane.org/gmane.linux.network/150198

With this patch, i tested vlans with both ipv4 and ipv6.

> 
> >  
> >  	err = -EINVAL;
> >  	if (sock->type == SOCK_DGRAM &&
> > -	    dev_hard_header(skb, dev, ntohs(proto), addr, NULL, len) < 0)
> > +	    (offset = dev_hard_header(skb, dev, ntohs(proto), addr, NULL, len)) < 0)
> >  		goto out_free;
> >  
> >  	/* Returns -EFAULT on error */
> > -	err = memcpy_fromiovec(skb_put(skb, len), msg->msg_iov, len);
> > +	err = skb_copy_datagram_from_iovec(skb, offset, msg->msg_iov, 0, len);
> >  	if (err)
> >  		goto out_free;
> >  
> > @@ -1127,6 +1182,51 @@ static int packet_snd(struct socket *sock,
> >  	skb->priority = sk->sk_priority;
> >  	skb->mark = sk->sk_mark;
> >  
> > +	if (po->vnet_hdr) {
> > +		skb_reset_mac_header(skb);
> > +		skb->protocol = eth_hdr(skb)->h_proto;
> > +
> 
> Is this also broken for vlans?

Same as above. 
> 
> > +		if (vnethdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
> > +			if (!skb_partial_csum_set(skb, vnethdr.csum_start,
> > +						  vnethdr.csum_offset)) {
> > +				err = -EINVAL;
> > +				goto out_free;
> > +			}
> > +		}
> > +
> > +		if (vnethdr.gso_type != VIRTIO_NET_HDR_GSO_NONE) {
> > +			switch (vnethdr.gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
> > +			case VIRTIO_NET_HDR_GSO_TCPV4:
> > +				skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;
> > +				break;
> > +			case VIRTIO_NET_HDR_GSO_TCPV6:
> > +				skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
> > +				break;
> > +			case VIRTIO_NET_HDR_GSO_UDP:
> > +				skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
> > +				break;
> > +			default:
> > +				err = -EINVAL;
> > +				goto out_free;
> > +			}
> > +
> > +			if (vnethdr.gso_type & VIRTIO_NET_HDR_GSO_ECN)
> > +				skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
> > +
> > +			skb_shinfo(skb)->gso_size = vnethdr.gso_size;
> > +			if (skb_shinfo(skb)->gso_size == 0) {
> > +				err = -EINVAL;
> > +				goto out_free;
> > +                	}
> > +
> > +			/* Header must be checked, and gso_segs computed. */
> > +			skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY;
> > +			skb_shinfo(skb)->gso_segs = 0;
> > +		}
> > +
> > +		len += sizeof(vnethdr);
> > +	}
> > +
> >  	/*
> >  	 *	Now send it
> >  	 */
> > @@ -1420,6 +1520,7 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock,
> >  	struct sk_buff *skb;
> >  	int copied, err;
> >  	struct sockaddr_ll *sll;
> > +	int vnet_hdr_len = 0;
> >  
> >  	err = -EINVAL;
> >  	if (flags & ~(MSG_PEEK|MSG_DONTWAIT|MSG_TRUNC|MSG_CMSG_COMPAT))
> > @@ -1451,6 +1552,44 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock,
> >  	if (skb == NULL)
> >  		goto out;
> >  
> > +	if (pkt_sk(sk)->vnet_hdr) {
> > +		struct virtio_net_hdr vnethdr = { 0 };
> > +
> > +		vnet_hdr_len = sizeof(vnethdr);
> > +		if ((len -= vnet_hdr_len) < 0)
> > +			return -EINVAL;
> > +
> > +		if (skb_is_gso(skb)) {
> > +			struct skb_shared_info *sinfo = skb_shinfo(skb);
> > +
> > +			/* This is a hint as to how much should be linear. */
> > +			vnethdr.hdr_len = skb_headlen(skb);
> > +			vnethdr.gso_size = sinfo->gso_size;
> > +			if (sinfo->gso_type & SKB_GSO_TCPV4)
> > +				vnethdr.gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
> > +			else if (sinfo->gso_type & SKB_GSO_TCPV6)
> > +				vnethdr.gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
> > +			else if (sinfo->gso_type & SKB_GSO_UDP)
> > +				vnethdr.gso_type = VIRTIO_NET_HDR_GSO_UDP;
> > +			else
> > +				BUG();
> 
> Is there any chance this can get SKB_GSO_FCOE by binding to
> an appropriate interface?  Maybe we don't want to BUG().
I could return -EINVAL in that case.

> 
> > +			if (sinfo->gso_type & SKB_GSO_TCP_ECN)
> > +				vnethdr.gso_type |= VIRTIO_NET_HDR_GSO_ECN;
> > +		} else
> > +			vnethdr.gso_type = VIRTIO_NET_HDR_GSO_NONE;
> > +
> > +		if (skb->ip_summed == CHECKSUM_PARTIAL) {
> > +			vnethdr.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
> > +			vnethdr.csum_start = skb->csum_start - skb_headroom(skb);
> > +			vnethdr.csum_offset = skb->csum_offset;
> > +		} /* else everything is zero */
> > +
> > +		if (unlikely(memcpy_toiovec(msg->msg_iov, (void *)&vnethdr,
> > +					    sizeof(vnethdr)))) {
> > +			return -EFAULT;
> > +		}
> > +	}
> > +
> >  	/*
> >  	 *	If the address length field is there to be filled in, we fill
> >  	 *	it in now.
> > @@ -1502,7 +1641,7 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock,
> >  	 *	Free or return the buffer as appropriate. Again this
> >  	 *	hides all the races and re-entrancy issues from us.
> >  	 */
> > -	err = (flags&MSG_TRUNC) ? skb->len : copied;
> > +	err = vnet_hdr_len + ((flags&MSG_TRUNC) ? skb->len : copied);
> >  
> >  out_free:
> >  	skb_free_datagram(sk, skb);
> > @@ -1826,6 +1965,22 @@ packet_setsockopt(struct socket *sock, int level, int optname, char __user *optv
> >  		po->origdev = !!val;
> >  		return 0;
> >  	}
> > +	case PACKET_VNET_HDR:
> > +	{
> > +		int val;
> > +
> > +		if (sock->type != SOCK_RAW)
> > +			return -EINVAL;
> > +		if (po->rx_ring.pg_vec || po->tx_ring.pg_vec)	
> > +			return -EBUSY;
> 
> Another way to get a broken ring + vnet hdr configuration
> would be to enable vnet hdr first and mmap second.
> I think we need to guard against this as well, by checking vnet_hdr
> when tx/rx ring is enabled.

OK. i will add a check when setting PACKET_RX_RING/TX_RING socket
options. 
> > +		if (optlen < sizeof(val))
> > +			return -EINVAL;
> > +		if (copy_from_user(&val, optval, sizeof(val)))
> > +			return -EFAULT;
> > +
> > +		po->vnet_hdr = !!val;
> > +		return 0;
> > +	}
> >  	default:
> >  		return -ENOPROTOOPT;
> >  	}
> > @@ -1876,6 +2031,13 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
> >  
> >  		data = &val;
> >  		break;
> > +	case PACKET_VNET_HDR:
> > +		if (len > sizeof(int))
> > +			len = sizeof(int);
> > +		val = po->vnet_hdr;
> > +
> > +		data = &val;
> > +		break;
> >  #ifdef CONFIG_PACKET_MMAP
> >  	case PACKET_VERSION:
> >  		if (len > sizeof(int))
> > 
> 

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