Re: [PATCH net-next 2/3] udp: move logic out of udp[46]_ufo_send_check

On Sat, Sep 20, 2014 at 6:12 PM, Eric Dumazet [off-list ref] wrote:

On Sat, 2014-09-20 at 14:52 -0700, Tom Herbert wrote:

quoted

In udp[46]_ufo_send_check the UDP checksum initialized to the pseudo
header checksum. We can move this logic into udp[46]_ufo_fragment.
After this change udp[64]_ufo_send_check is a no-op.

Signed-off-by: Tom Herbert <redacted>
---
 net/ipv4/udp_offload.c | 37 +++++++++++++++----------------------
 net/ipv6/udp_offload.c | 40 ++++++++++++++++++----------------------
 2 files changed, 33 insertions(+), 44 deletions(-)

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index d7c43f7..2918cc9 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c

@@ -27,23 +27,6 @@ struct udp_offload_priv {

 static int udp4_ufo_send_check(struct sk_buff *skb)
 {
-     if (!pskb_may_pull(skb, sizeof(struct udphdr)))
-             return -EINVAL;
-
-     if (likely(!skb->encapsulation)) {
-             const struct iphdr *iph;
-             struct udphdr *uh;
-
-             iph = ip_hdr(skb);
-             uh = udp_hdr(skb);
-
-             uh->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr, skb->len,
-                             IPPROTO_UDP, 0);
-             skb->csum_start = skb_transport_header(skb) - skb->head;
-             skb->csum_offset = offsetof(struct udphdr, check);
-             skb->ip_summed = CHECKSUM_PARTIAL;
-     }
-
      return 0;
 }

@@ -128,8 +111,9 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 {
      struct sk_buff *segs = ERR_PTR(-EINVAL);
      unsigned int mss;
-     int offset;
      __wsum csum;
+     struct udphdr *uh;
+     struct iphdr *iph;

      if (skb->encapsulation &&
          (skb_shinfo(skb)->gso_type &

@@ -138,6 +122,9 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
              goto out;
      }

+     if (!pskb_may_pull(skb, sizeof(struct udphdr)))
+             goto out;
+
      mss = skb_shinfo(skb)->gso_size;
      if (unlikely(skb->len <= mss))
              goto out;

@@ -165,10 +152,16 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
       * HW cannot do checksum of UDP packets sent as multiple
       * IP fragments.
       */
-     offset = skb_checksum_start_offset(skb);
-     csum = skb_checksum(skb, offset, skb->len - offset, 0);
-     offset += skb->csum_offset;
-     *(__sum16 *)(skb->data + offset) = csum_fold(csum);
+
+     uh = udp_hdr(skb);
+     iph = ip_hdr(skb);
+
+     uh->check = 0;
+     csum = skb_checksum(skb, 0, skb->len, 0);
+     uh->check = udp_v4_check(skb->len, iph->saddr, iph->daddr, csum);
+     if (uh->check == 0)
+             uh->check = CSUM_MANGLED_0;
+
      skb->ip_summed = CHECKSUM_NONE;

Shouldn't it be changed to CHECKSUM_PARTIAL or something ?

udp4_ufo_send_check() was able to fill CHECKSUM_PARTIAL,
I fear I do not understand enough this part.

Right, I had tried that also. Didn't work, IIRC there was a crash
later on because csum_start wasn't initialized.