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Date:	Wed, 02 Jul 2014 23:49:02 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
Cc:	Steffen Klassert <steffen.klassert@...unet.com>,
	Mathias Krause <minipli@...glemail.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Thomas Graf <tgraf@...g.ch>, Joe Perches <joe@...ches.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH net-next v2 3/3 RFC] pktgen: Allow sending TCP packets

On Wed, 2014-07-02 at 20:54 +0100, Zoltan Kiss wrote:
> This is a prototype patch to enable sending TCP packets with pktgen. The
> original motivation is to test TCP GSO with xen-netback/netfront, but I'm not
> sure about how the checksum should be set up, and also someone should verify the
> GSO settings I'm using.
> 

It seems you only took care of IPv6, but did not mention this in the
changelog.

> Signed-off-by: Zoltan Kiss <zoltan.kiss@...rix.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Thomas Graf <tgraf@...g.ch>
> Cc: Joe Perches <joe@...ches.com>
> Cc: netdev@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: xen-devel@...ts.xenproject.org
> ---
> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
> index d7206ea..13aad46 100644
> --- a/net/core/pktgen.c
> +++ b/net/core/pktgen.c
> @@ -203,6 +203,7 @@
>  #define F_NODE          (1<<15)	/* Node memory alloc*/
>  #define F_UDPCSUM       (1<<16)	/* Include UDP checksum */
>  #define F_PATTERN       (1<<17)	/* Fill the payload with a pattern */
> +#define F_TCP           (1<<18)	/* Send TCP packet instead of UDP */
>  
>  /* Thread control flag bits */
>  #define T_STOP        (1<<0)	/* Stop run */
> @@ -1343,6 +1344,12 @@ static ssize_t pktgen_if_write(struct file *file,
>  		else if (strcmp(f, "!PATTERN") == 0)
>  			pkt_dev->flags &= ~F_PATTERN;
>  
> +		else if (strcmp(f, "TCP") == 0)
> +			pkt_dev->flags |= F_TCP;
> +
> +		else if (strcmp(f, "!TCP") == 0)
> +			pkt_dev->flags &= ~F_TCP;
> +
>  		else {
>  			sprintf(pg_result,
>  				"Flag -:%s:- unknown\nAvailable flags, (prepend ! to un-set flag):\n%s",
> @@ -2952,6 +2959,7 @@ static struct sk_buff *fill_packet_ipv4(struct net_device *odev,
>  	struct sk_buff *skb = NULL;
>  	__u8 *eth;
>  	struct udphdr *udph;
> +	struct tcphdr *tcph;
>  	int datalen, iplen;
>  	struct iphdr *iph;
>  	__be16 protocol = htons(ETH_P_IP);
> @@ -3013,29 +3021,39 @@ static struct sk_buff *fill_packet_ipv4(struct net_device *odev,
>  	iph = (struct iphdr *) skb_put(skb, sizeof(struct iphdr));
>  
>  	skb_set_transport_header(skb, skb->len);
> -	udph = (struct udphdr *) skb_put(skb, sizeof(struct udphdr));
> +
> +	if (pkt_dev->flags & F_TCP) {
> +		datalen = pkt_dev->cur_pkt_size - ETH_HLEN - 20 -
> +			  sizeof(struct tcphdr) - pkt_dev->pkt_overhead;
> +		tcph = (struct tcphdr *)skb_put(skb, sizeof(struct tcphdr));
> +		tcph->source = htons(pkt_dev->cur_udp_src);
> +		tcph->dest = htons(pkt_dev->cur_udp_dst);
> +		tcph->check = 0;

You do not clear other fields, thus leaking kernel memory.

> +	} else {
> +		datalen = pkt_dev->cur_pkt_size - ETH_HLEN - 20 -
> +			  sizeof(struct udphdr) - pkt_dev->pkt_overhead;
> +		udph = (struct udphdr *)skb_put(skb, sizeof(struct udphdr));
> +		udph->source = htons(pkt_dev->cur_udp_src);
> +		udph->dest = htons(pkt_dev->cur_udp_dst);
> +		udph->len = htons(datalen + sizeof(struct udphdr));	/* DATA + udphdr */
> +		udph->check = 0;
> +	}
> +
>  	skb_set_queue_mapping(skb, queue_map);
>  	skb->priority = pkt_dev->skb_priority;
>  
>  	memcpy(eth, pkt_dev->hh, 12);
>  	*(__be16 *) & eth[12] = protocol;
>  
> -	/* Eth + IPh + UDPh + mpls */
> -	datalen = pkt_dev->cur_pkt_size - 14 - 20 - 8 -
> -		  pkt_dev->pkt_overhead;
>  	if (datalen < 0 || datalen < sizeof(struct pktgen_hdr))
>  		datalen = sizeof(struct pktgen_hdr);
>  
> -	udph->source = htons(pkt_dev->cur_udp_src);
> -	udph->dest = htons(pkt_dev->cur_udp_dst);
> -	udph->len = htons(datalen + 8);	/* DATA + udphdr */
> -	udph->check = 0;
>  
>  	iph->ihl = 5;
>  	iph->version = 4;
>  	iph->ttl = 32;
>  	iph->tos = pkt_dev->tos;
> -	iph->protocol = IPPROTO_UDP;	/* UDP */
> +	iph->protocol = pkt_dev->flags & F_TCP ? IPPROTO_TCP : IPPROTO_UDP;
>  	iph->saddr = pkt_dev->cur_saddr;
>  	iph->daddr = pkt_dev->cur_daddr;
>  	iph->id = htons(pkt_dev->ip_id);
> @@ -3050,7 +3068,9 @@ static struct sk_buff *fill_packet_ipv4(struct net_device *odev,
>  
>  	if (!(pkt_dev->flags & F_UDPCSUM)) {
>  		skb->ip_summed = CHECKSUM_NONE;
> -	} else if (odev->features & NETIF_F_V4_CSUM) {
> +	} else if (pkt_dev->flags & F_TCP)
> +		skb_checksum_setup(skb, true);
> +	else if (odev->features & NETIF_F_V4_CSUM) {
>  		skb->ip_summed = CHECKSUM_PARTIAL;
>  		skb->csum = 0;
>  		udp4_hwcsum(skb, udph->source, udph->dest);
> @@ -3067,6 +3087,18 @@ static struct sk_buff *fill_packet_ipv4(struct net_device *odev,
>  
>  	pktgen_finalize_skb(pkt_dev, skb, datalen);
>  
> +	if (odev->mtu < skb->len) {
> +		skb_shinfo(skb)->gso_size = odev->mtu - ETH_HLEN - 20 -
> +					    pkt_dev->pkt_overhead;
> +		if (pkt_dev->flags & F_TCP) {
> +			skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;
> +			skb_shinfo(skb)->gso_size -= sizeof(struct tcphdr);
> +		} else {
> +			skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
> +			skb_shinfo(skb)->gso_size -= sizeof(struct udphdr);
> +		}
> +	}

Some NIC do not handle TSO, and driver could crash if they have sanity
tests.

pktgen directly calls driver ndo_start_xmit(), so we need to make sure
we give valid packets to the driver (no software fallbacks at this
stage)


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