On 11/16/2015 09:02 PM, Tom Herbert wrote:
On Mon, Nov 16, 2015 at 4:20 PM, Ben Greear <gree...@candelatech.com> wrote:
Hello!
I'm hacking on (my already hacked) pktgen, trying to get it to send TCP
frames.
And, having issues getting checksums to work properly.
I'm trying this:
struct iphdr *iph = ip_hdr(skb);
struct net_device *odev = pkt_dev->odev;
if (pkt_dev->flags & F_TCP) {
if (odev->features & NETIF_F_V4_CSUM) {
skb->ip_summed = CHECKSUM_PARTIAL;
} else {
skb->ip_summed = CHECKSUM_NONE;
}
skb->csum = 0;
__tcp_v4_send_check(skb, iph->saddr, iph->daddr);
I added an export so I could call that __tcp_v4_send_check method
w/out having to put a fake socket struct on the stack.
But, the receiving NIC reports 100% checksum failure, so obviously
I'm not doing it correct.
Any suggestions on what I might be doing wrong or the proper method(s)
to call?
It's really hard to tell what is happening without seeing the full
patch your using. Maybe you're not setting the TCP correctly or
transport header is not set right in skb.
Ok, I have this working now.. at least in my current setup.
Main problem is that TCP stack uses skb->len before the other transport
headers are counted in skb->len, it appears.
So, in pktgen I need to subtract out the pkt prefix. This at least
makes the hw-accel path work...not sure about software csum path yet...
static void pg_do_csum(struct pktgen_dev *pkt_dev, struct sk_buff *skb) {
struct iphdr *iph = ip_hdr(skb);
struct udphdr *uh;
struct net_device *odev = pkt_dev->odev;
if (pkt_dev->flags & F_TCP) {
struct tcphdr *th = tcp_hdr(skb);
unsigned int prefix_len = (unsigned int)((unsigned char*)th -
skb->data);
if (odev->features & NETIF_F_V4_CSUM) {
skb->ip_summed = CHECKSUM_PARTIAL;
/* Subtract out IP hdr and before */
th->check = ~tcp_v4_check(skb->len - prefix_len,
iph->saddr, iph->daddr, 0);
skb->csum_start = skb_transport_header(skb) - skb->head;
skb->csum_offset = offsetof(struct tcphdr, check);
} else {
skb->ip_summed = CHECKSUM_NONE;
th->check = 0;
skb->csum = 0;
th->check = tcp_v4_check(skb->len - prefix_len,
iph->saddr, iph->daddr,
csum_partial(th, th->doff << 2,
skb->csum));
}
} else {
Thanks,
Ben
--
Ben Greear <gree...@candelatech.com>
Candela Technologies Inc http://www.candelatech.com
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