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SubjectRe: TCP Segmentation Offloading (TSO)
Date
Hello!

> [1] Kudos to

Hmm... wait awhile with celebrating, the implementation in tcp is still
at level of a toy. Well, and it happens to crash, the patch is enclosed.

Alexey


--- linux/net/ipv4/tcp_output.c.orig Sat Aug 31 17:43:36 2002
+++ linux/net/ipv4/tcp_output.c Mon Sep 2 22:48:16 2002
@@ -477,6 +477,56 @@
return 0;
}

+/* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
+ * eventually). The difference is that pulled data not copied, but
+ * immediately discarded.
+ */
+unsigned char * __pskb_trim_head(struct sk_buff *skb, int len)
+{
+ int i, k, eat;
+
+ eat = len;
+ k = 0;
+ for (i=0; i<skb_shinfo(skb)->nr_frags; i++) {
+ if (skb_shinfo(skb)->frags[i].size <= eat) {
+ put_page(skb_shinfo(skb)->frags[i].page);
+ eat -= skb_shinfo(skb)->frags[i].size;
+ } else {
+ skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
+ if (eat) {
+ skb_shinfo(skb)->frags[k].page_offset += eat;
+ skb_shinfo(skb)->frags[k].size -= eat;
+ eat = 0;
+ }
+ k++;
+ }
+ }
+ skb_shinfo(skb)->nr_frags = k;
+
+ skb->tail = skb->data;
+ skb->data_len -= len;
+ skb->len = skb->data_len;
+ return skb->tail;
+}
+
+static int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
+{
+ if (skb_cloned(skb) &&
+ pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+ return -ENOMEM;
+
+ if (len <= skb_headlen(skb)) {
+ __skb_pull(skb, len);
+ } else {
+ if (__pskb_trim_head(skb, len-skb_headlen(skb)) == NULL)
+ return -ENOMEM;
+ }
+
+ TCP_SKB_CB(skb)->seq += len;
+ skb->ip_summed = CHECKSUM_HW;
+ return 0;
+}
+
/* This function synchronize snd mss to current pmtu/exthdr set.

tp->user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
@@ -836,8 +886,6 @@
return -EAGAIN;

if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
- struct sk_buff *skb2;
-
if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
BUG();

@@ -847,13 +895,8 @@
tp->mss_cache = tp->mss_cache_std;
}

- if(tcp_fragment(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
+ if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
return -ENOMEM;
-
- skb2 = skb->next;
- __skb_unlink(skb, skb->list);
- tcp_free_skb(sk, skb);
- skb = skb2;
}

/* If receiver has shrunk his window, and skb is out of
-
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