Re: [Xen-devel] [PATCH net-next v3 4/4 RFC] pktgen: Allow sending IPv4 TCP packets

[David Miller <davem@xxxxxxxxxxxxx>]

From: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
Date: Wed, 30 Jul 2014 17:20:12 +0100

> This is a prototype patch to enable sending IPv4 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.
> 
> Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Thomas Graf <tgraf@xxxxxxx>
> Cc: Joe Perches <joe@xxxxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> ---
> v3:
> - mention explicitly that this for IPv4
> - memset the TCP header and set up doff
> - rework of checksum handling and GSO setting in fill_packet_ipv4
> - bail out in pktgen_xmit if the device won't be able to handle GSO
> 
> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
> index 0d0aaac..9d93bda 100644
> --- a/net/core/pktgen.c
> +++ b/net/core/pktgen.c
> @@ -162,6 +162,7 @@
>  #include <net/checksum.h>
>  #include <net/ipv6.h>
>  #include <net/udp.h>
> +#include <net/tcp.h>
>  #include <net/ip6_checksum.h>
>  #include <net/addrconf.h>
>  #ifdef CONFIG_XFRM
> @@ -203,6 +204,7 @@
>  #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 */
> @@ -664,6 +666,9 @@ static int pktgen_if_show(struct seq_file *seq, void *v)
>       if (pkt_dev->flags & F_PATTERN)
>               seq_puts(seq, "PATTERN  ");
>  
> +     if (pkt_dev->flags & F_TCP)
> +             seq_puts(seq, "TCP  ");
> +
>       if (pkt_dev->flags & F_MPLS_RND)
>               seq_puts(seq,  "MPLS_RND  ");
>  
> @@ -1342,6 +1347,12 @@ 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",
> @@ -2955,7 +2966,8 @@ static struct sk_buff *fill_packet_ipv4(struct 
> net_device *odev,
>  {
>       struct sk_buff *skb = NULL;
>       __u8 *eth;
> -     struct udphdr *udph;
> +     struct udphdr *udph = NULL;
> +     struct tcphdr *tcph;
>       int datalen, iplen;
>       struct iphdr *iph;
>       __be16 protocol = htons(ETH_P_IP);
> @@ -3017,29 +3029,40 @@ 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));
> +             memset(tcph, 0, sizeof(*tcph));
> +             tcph->source = htons(pkt_dev->cur_udp_src);
> +             tcph->dest = htons(pkt_dev->cur_udp_dst);
> +             tcph->doff = sizeof(struct tcphdr) >> 2;
> +     } 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));
> +             udph->check = 0;
> +     }
> +

As more protocols (SCTP, etc.) get supported, this is going to become
completely unmanageable.  Please use callbacks or something like that
so this function doesn't turn into even more spaghetti.

> +     } else if (pkt_dev->flags & F_TCP) {
> +             struct inet_sock inet;
> +
> +             inet.inet_saddr = iph->saddr;
> +             inet.inet_daddr = iph->daddr;
> +             skb->ip_summed = CHECKSUM_NONE;
> +             tcp_v4_send_check((struct sock *)&inet, skb);

Please don't do things like this.  Making fake sockets on the stack, don't
do it.

Do other non-socket contexts compute TCP checksums this way?  Check
netfilter or similar, see what they do.

Worst case export __tcp_v4_send_check() or just duplicate it's contents
in the tcp case here.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel