Subject: Re: [PATCH net-next v3] xen-netfront: Add support for IPv6 offloads

From: Boris Ostrovsky <[email-masked]>
Date: Tue, 31 Dec 2013 14:10:09 -0500

On 11/26/2013 11:41 AM, Paul Durrant wrote:
> This patch adds support for IPv6 checksum offload and GSO when those
> features are available in the backend.

Sorry for late review. Mostly style comments.

>
> Signed-off-by: Paul Durrant <[email-masked]>
> Cc: Konrad Rzeszutek Wilk <[email-masked]>
> Cc: Boris Ostrovsky <[email-masked]>
> Cc: David Vrabel <[email-masked]>
> Cc: Ian Campbell <[email-masked]>
> Cc: Wei Liu <[email-masked]>
> Cc: Annie Li <[email-masked]>
> ---
>
> v3:
>   - Addressed comments raised by Annie Li
>
> v2:
>   - Addressed comments raised by Ian Campbell
>
>   drivers/net/xen-netfront.c |  239 ++++++++++++++++++++++++++++++++++++++++----
>   include/linux/ipv6.h       |    2 +
>   2 files changed, 224 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index dd1011e..fe747e4 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -616,7 +616,9 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
>   		tx->flags |= XEN_NETTXF_extra_info;
>   
>   		gso->u.gso.size = skb_shinfo(skb)->gso_size;
> -		gso->u.gso.type = XEN_NETIF_GSO_TYPE_TCPV4;
> +		gso->u.gso.type = (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6) ?
> +			          XEN_NETIF_GSO_TYPE_TCPV6 :
> +			          XEN_NETIF_GSO_TYPE_TCPV4;
>   		gso->u.gso.pad = 0;
>   		gso->u.gso.features = 0;
>   
> @@ -808,15 +810,18 @@ static int xennet_set_skb_gso(struct sk_buff *skb,
>   		return -EINVAL;
>   	}
>   
> -	/* Currently only TCPv4 S.O. is supported. */
> -	if (gso->u.gso.type != XEN_NETIF_GSO_TYPE_TCPV4) {
> +	if (gso->u.gso.type != XEN_NETIF_GSO_TYPE_TCPV4 &&
> +	    gso->u.gso.type != XEN_NETIF_GSO_TYPE_TCPV6) {
>   		if (net_ratelimit())
>   			pr_warn("Bad GSO type %d\n", gso->u.gso.type);
>   		return -EINVAL;
>   	}
>   
>   	skb_shinfo(skb)->gso_size = gso->u.gso.size;
> -	skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;
> +	skb_shinfo(skb)->gso_type =
> +		(gso->u.gso.type == XEN_NETIF_GSO_TYPE_TCPV4) ?
> +		SKB_GSO_TCPV4 :
> +		SKB_GSO_TCPV6;
>   
>   	/* Header must be checked, and gso_segs computed. */
>   	skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY;
> @@ -856,11 +861,42 @@ static RING_IDX xennet_fill_frags(struct netfront_info *np,
>   	return cons;
>   }
>   
> -static int checksum_setup(struct net_device *dev, struct sk_buff *skb)
> +static inline bool maybe_pull_tail(struct sk_buff *skb, unsigned int min,
> +				   unsigned int max)

Should this routine return error code instead of a boolean? Otherwise 
it's not clear what "false" should mean --- whether it is that it failed 
to pull or that the pull wasn't needed.

>   {
> -	struct iphdr *iph;
> -	int err = -EPROTO;
> +	int target;
> +
> +	BUG_ON(max < min);
> +
> +	if (!skb_is_nonlinear(skb) || skb_headlen(skb) >= min)
> +		return true;
> +
> +	/* If we need to pullup then pullup to max, so we hopefully
> +	 * won't need to do it again.
> +	 */

Comment style.

> +	target = min_t(int, skb->len, max);
> +	__pskb_pull_tail(skb, target - skb_headlen(skb));
> +
> +	if (skb_headlen(skb) < min) {

Why not explicitly check whether__pskb_pull_tail() returned NULL ?

> +		net_err_ratelimited("Failed to pullup packet header\n");
> +		return false;
> +	}
> +
> +	return true;
> +}
> +
> +/* This value should be large enough to cover a tagged ethernet header plus
> + * maximally sized IP and TCP or UDP headers.
> + */

Comment style.

> +#define MAX_IP_HEADER 128
> +
> +static int checksum_setup_ip(struct net_device *dev, struct sk_buff *skb)
> +{
> +	struct iphdr *iph = (void *)skb->data;
> +	unsigned int header_size;
> +	unsigned int off;
>   	int recalculate_partial_csum = 0;
> +	int err = -EPROTO;
>   
>   	/*
>   	 * A GSO SKB must be CHECKSUM_PARTIAL. However some buggy
> @@ -879,40 +915,158 @@ static int checksum_setup(struct net_device *dev, struct sk_buff *skb)
>   	if (skb->ip_summed != CHECKSUM_PARTIAL)
>   		return 0;
>   
> -	if (skb->protocol != htons(ETH_P_IP))
> +	off = sizeof(struct iphdr);
> +
> +	header_size = skb->network_header + off;
> +	if (!maybe_pull_tail(skb, header_size, MAX_IP_HEADER))
>   		goto out;
>   
> -	iph = (void *)skb->data;
> +	off = iph->ihl * 4;
>   
>   	switch (iph->protocol) {
>   	case IPPROTO_TCP:
> -		if (!skb_partial_csum_set(skb, 4 * iph->ihl,
> +		if (!skb_partial_csum_set(skb, off,
>   					  offsetof(struct tcphdr, check)))
>   			goto out;
>   
>   		if (recalculate_partial_csum) {
>   			struct tcphdr *tcph = tcp_hdr(skb);
> +
> +			header_size = skb->network_header +
> +				off +
> +				sizeof(struct tcphdr);

You can put these (off and sizeof) onto the same line.

> +			if (!maybe_pull_tail(skb, header_size, MAX_IP_HEADER))
> +				goto out;
> +
>   			tcph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
> -							 skb->len - iph->ihl*4,
> +							 skb->len - off,
>   							 IPPROTO_TCP, 0);
>   		}
>   		break;
>   	case IPPROTO_UDP:
> -		if (!skb_partial_csum_set(skb, 4 * iph->ihl,
> +		if (!skb_partial_csum_set(skb, off,
>   					  offsetof(struct udphdr, check)))
>   			goto out;
>   
>   		if (recalculate_partial_csum) {
>   			struct udphdr *udph = udp_hdr(skb);
> +
> +			header_size = skb->network_header +
> +				off +
> +				sizeof(struct udphdr);
> +			if (!maybe_pull_tail(skb, header_size, MAX_IP_HEADER))
> +				goto out;
> +
>   			udph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
> -							 skb->len - iph->ihl*4,
> +							 skb->len - off,
>   							 IPPROTO_UDP, 0);
>   		}
>   		break;
>   	default:
> -		if (net_ratelimit())
> -			pr_err("Attempting to checksum a non-TCP/UDP packet, dropping a protocol %d packet\n",
> -			       iph->protocol);
> +		net_err_ratelimited("Attempting to checksum a non-TCP/UDP packet, dropping a protocol %d packet\n",
> +				    iph->protocol);
> +		goto out;
> +	}
> +
> +	err = 0;
> +
> +out:
> +	return err;
> +}
> +
> +/* This value should be large enough to cover a tagged ethernet header plus
> + * an IPv6 header, all options, and a maximal TCP or UDP header.
> + */
> +#define MAX_IPV6_HEADER 256
> +
> +static int checksum_setup_ipv6(struct net_device *dev, struct sk_buff *skb)
> +{
> +	struct ipv6hdr *ipv6h = (void *)skb->data;
> +	u8 nexthdr;
> +	unsigned int header_size;
> +	unsigned int off;
> +	bool fragment;
> +	bool done;
> +	int err = -EPROTO;
> +
> +	done = false;

This should probably be moved down to the beginning of the while loop. 
And you also need to initialize fragment to "false" (and possibly rename 
it to is_fragment?)

> +
> +	/* A non-CHECKSUM_PARTIAL SKB does not require setup. */
> +	if (skb->ip_summed != CHECKSUM_PARTIAL)
> +		return 0;
> +
> +	off = sizeof(struct ipv6hdr);
> +
> +	header_size = skb->network_header + off;
> +	if (!maybe_pull_tail(skb, header_size, MAX_IPV6_HEADER))
> +		goto out;
> +
> +	nexthdr = ipv6h->nexthdr;
> +
> +	while ((off <= sizeof(struct ipv6hdr) + ntohs(ipv6h->payload_len)) &&
> +	       !done) {
> +		switch (nexthdr) {
> +		case IPPROTO_DSTOPTS:
> +		case IPPROTO_HOPOPTS:
> +		case IPPROTO_ROUTING: {
> +			struct ipv6_opt_hdr *hp = (void *)(skb->data + off);
> +
> +			header_size = skb->network_header +
> +				off +
> +				sizeof(struct ipv6_opt_hdr);

I'd merge the last two lines.

> +			if (!maybe_pull_tail(skb, header_size, MAX_IPV6_HEADER))
> +				goto out;
> +
> +			nexthdr = hp->nexthdr;
> +			off += ipv6_optlen(hp);
> +			break;
> +		}
> +		case IPPROTO_AH: {
> +			struct ip_auth_hdr *hp = (void *)(skb->data + off);
> +
> +			header_size = skb->network_header +
> +				off +
> +				sizeof(struct ip_auth_hdr);

Here as well.

> +			if (!maybe_pull_tail(skb, header_size, MAX_IPV6_HEADER))
> +				goto out;
> +
> +			nexthdr = hp->nexthdr;
> +			off += ipv6_ahlen(hp);
> +			break;
> +		}
> +		case IPPROTO_FRAGMENT:
> +			fragment = true;
> +			/* fall through */
> +		default:
> +			done = true;
> +			break;
> +		}
> +	}
> +
> +	if (!done) {
> +		net_err_ratelimited("Failed to parse packet header\n");
> +		goto out;
> +	}
> +
> +	if (fragment) {
> +		net_err_ratelimited("Packet is a fragment!\n");
> +		goto out;
> +	}
> +
> +	switch (nexthdr) {
> +	case IPPROTO_TCP:
> +		if (!skb_partial_csum_set(skb, off,
> +					  offsetof(struct tcphdr, check)))
> +			goto out;
> +		break;
> +	case IPPROTO_UDP:
> +		if (!skb_partial_csum_set(skb, off,
> +					  offsetof(struct udphdr, check)))
> +			goto out;
> +		break;
> +	default:
> +		net_err_ratelimited("Attempting to checksum a non-TCP/UDP packet, dropping a protocol %d packet\n",
> +				    nexthdr);
>   		goto out;
>   	}
>   
> @@ -922,6 +1076,25 @@ out:
>   	return err;
>   }
>   
> +static int checksum_setup(struct net_device *dev, struct sk_buff *skb)
> +{
> +	int err;

Initialize to -EPROTO (just to keep consistent with the rest of the file)

> +
> +	switch (skb->protocol) {
> +	case htons(ETH_P_IP):
> +		err = checksum_setup_ip(dev, skb);
> +		break;
> +	case htons(ETH_P_IPV6):
> +		err = checksum_setup_ipv6(dev, skb);
> +		break;
> +	default:
> +		err = -EPROTO;
> +		break;
> +	}
> +
> +	return err;
> +}
> +
>   static int handle_incoming_queue(struct net_device *dev,
>   				 struct sk_buff_head *rxq)
>   {
> @@ -1232,6 +1405,15 @@ static netdev_features_t xennet_fix_features(struct net_device *dev,
>   			features &= ~NETIF_F_SG;
>   	}
>   
> +	if (features & NETIF_F_IPV6_CSUM) {
> +		if (xenbus_scanf(XBT_NIL, np->xbdev->otherend,
> +				 "feature-ipv6-csum-offload", "%d", &val) < 0)
> +			val = 0;
> +
> +		if (!val)
> +			features &= ~NETIF_F_IPV6_CSUM;
> +	}
> +
>   	if (features & NETIF_F_TSO) {
>   		if (xenbus_scanf(XBT_NIL, np->xbdev->otherend,
>   				 "feature-gso-tcpv4", "%d", &val) < 0)
> @@ -1241,6 +1423,15 @@ static netdev_features_t xennet_fix_features(struct net_device *dev,
>   			features &= ~NETIF_F_TSO;
>   	}
>   
> +	if (features & NETIF_F_TSO6) {
> +		if (xenbus_scanf(XBT_NIL, np->xbdev->otherend,
> +				 "feature-gso-tcpv6", "%d", &val) < 0)
> +			val = 0;
> +
> +		if (!val)
> +			features &= ~NETIF_F_TSO6;
> +	}
> +
>   	return features;
>   }
>   
> @@ -1373,7 +1564,9 @@ static struct net_device *xennet_create_dev(struct xenbus_device *dev)
>   	netif_napi_add(netdev, &np->napi, xennet_poll, 64);
>   	netdev->features        = NETIF_F_IP_CSUM | NETIF_F_RXCSUM |
>   				  NETIF_F_GSO_ROBUST;
> -	netdev->hw_features	= NETIF_F_IP_CSUM | NETIF_F_SG | NETIF_F_TSO;
> +	netdev->hw_features	= NETIF_F_SG |
> +		                  NETIF_F_IPV6_CSUM |
> +		                  NETIF_F_TSO | NETIF_F_TSO6;

Can you merge these three lines and stay under 80? If not, merge either 
of the two of them.

-boris

>   
>   	/*
>            * Assume that all hw features are available for now. This set
> @@ -1751,6 +1944,18 @@ again:
>   		goto abort_transaction;
>   	}
>   
> +	err = xenbus_printf(xbt, dev->nodename, "feature-gso-tcpv6", "%d", 1);
> +	if (err) {
> +		message = "writing feature-gso-tcpv6";
> +		goto abort_transaction;
> +	}
> +
> +	err = xenbus_printf(xbt, dev->nodename, "feature-ipv6-csum-offload", "%d", 1);
> +	if (err) {
> +		message = "writing feature-ipv6-csum-offload";
> +		goto abort_transaction;
> +	}
> +
>   	err = xenbus_transaction_end(xbt, 0);
>   	if (err) {
>   		if (err == -EAGAIN)
> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
> index 5d89d1b..10f1b03 100644
> --- a/include/linux/ipv6.h
> +++ b/include/linux/ipv6.h
> @@ -4,6 +4,8 @@
>   #include <uapi/linux/ipv6.h>
>   
>   #define ipv6_optlen(p)  (((p)->hdrlen+1) << 3)
> +#define ipv6_ahlen(p)   (((p)->hdrlen+2) << 2);
> +
>   /*
>    * This structure contains configuration options per IPv6 link.
>    */