kk Blog —— 通用基础

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skb 数据异或

skb 数据异或,可以改进成单独的option

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diff --git a/run.sh b/run.sh
index 138e664..0eb5286 100755
--- a/run.sh
+++ b/run.sh
@@ -19,3 +19,4 @@ echo 10000 > /proc/sys/net/tcp/digest/digest_err_retry
 echo 0 > /proc/sys/net/ipv4/tcp_timestamps # for mptcp+digest
 
 echo 0 > /proc/sys/net/tcp/mss_adjust
+echo 0 > /proc/sys/net/tcp/digest/digest_xor
diff --git a/src/4.15.18/tcp_ipv4.c b/src/4.15.18/tcp_ipv4.c
index b1b5c9d..b94ba6e 100644
--- a/src/4.15.18/tcp_ipv4.c
+++ b/src/4.15.18/tcp_ipv4.c
@@ -1848,6 +1848,12 @@ int tcp_v4_rcv(struct sk_buff *skb)
  th = (const struct tcphdr *)skb->data;
  iph = ip_hdr(skb);
 
+ if (digest_xor && digest_skb_check(NULL, NULL, skb, 0) != 0) {
+     int idx = 0;
+     skb->ip_summed = CHECKSUM_UNNECESSARY;
+     skb_change_bits(skb, th->doff * 4, skb->len - th->doff * 4, &idx);
+ }
+
 lookup:
  sk = __inet_lookup_skb(&tcp_hashinfo, skb, __tcp_hdrlen(th), th->source,
                 th->dest, sdif, &refcounted);
diff --git a/src/4.15.18/tcp_ipv6.c b/src/4.15.18/tcp_ipv6.c
index 3e27967..e975356 100644
--- a/src/4.15.18/tcp_ipv6.c
+++ b/src/4.15.18/tcp_ipv6.c
@@ -1619,6 +1619,12 @@ int tcp_v6_rcv(struct sk_buff *skb)
  th = (const struct tcphdr *)skb->data;
  hdr = ipv6_hdr(skb);
 
+ if (digest_xor && digest_skb_check(NULL, NULL, skb, 0) != 0) {
+     int idx = 0;
+     skb->ip_summed = CHECKSUM_UNNECESSARY;
+     skb_change_bits(skb, th->doff * 4, skb->len - th->doff * 4, &idx);
+ }
+
 lookup:
  sk = __inet6_lookup_skb(&tcp_hashinfo, skb, __tcp_hdrlen(th),
              th->source, th->dest, inet6_iif(skb), sdif,
diff --git a/src/4.15.18/tcp_output.c b/src/4.15.18/tcp_output.c
index dab8703..f766ff4 100644
--- a/src/4.15.18/tcp_output.c
+++ b/src/4.15.18/tcp_output.c
@@ -1118,6 +1118,9 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
      oskb = skb;
 
      tcp_skb_tsorted_save(oskb) {
+         if (digest_xor)
+             skb = skb_copy(oskb, gfp_mask);
+         else
          if (unlikely(skb_cloned(oskb)))
              skb = pskb_copy(oskb, gfp_mask);
          else
@@ -1264,6 +1267,13 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
      sk_nocaps_add(sk, NETIF_F_GSO_MASK);
 
      merge = !(tcb->tcp_flags & TCPHDR_SYN);
+
+     if (digest_xor) {
+         int idx = 0;
+         skb_change_bits(skb, tcp_header_size, skb->len - tcp_header_size, &idx);
+         skb->ip_summed = CHECKSUM_NONE;
+         skb->csum = skb_checksum(skb, tcp_header_size, skb->len - tcp_header_size, 0);
+     }
  }
 
  tcp_options_write((__be32 *)(th + 1), tp, &opts, skb, merge);
@@ -3122,6 +3132,9 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
      struct sk_buff *nskb;
 
      tcp_skb_tsorted_save(skb) {
+         if (digest_xor)
+             nskb = skb_copy(skb, GFP_ATOMIC);
+         else
          nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC);
          err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
                   -ENOBUFS;
diff --git a/src/digest_core.c b/src/digest_core.c
index 54af869..50840b1 100644
--- a/src/digest_core.c
+++ b/src/digest_core.c
@@ -419,9 +419,106 @@ out:
  return 0;
 }
 
+
+int digest_xor = 0;
+unsigned char MY_XOR[65536];
+
+int __skb_change_bits(unsigned char *from, int len, int *idx)
+{
+ int i;
+ for (i = 0; i < len; i ++) {
+     *(from + i) ^= MY_XOR[*idx];
+     *idx = *idx + 1;
+ }
+ return 0;
+}
+
+int skb_change_bits(struct sk_buff *skb, int offset, int len, int *idx)
+{
+ int start = skb_headlen(skb);
+ struct sk_buff *frag_iter;
+ int i, copy;
+
+ if (offset > (int)skb->len - len)
+     goto fault;
+
+ /* Copy header. */
+ if ((copy = start - offset) > 0) {
+     if (copy > len)
+         copy = len;
+     // skb_copy_from_linear_data_offset(skb, offset, to, copy);
+     __skb_change_bits(skb->data + offset, copy, idx);
+     if ((len -= copy) == 0)
+         return 0;
+     offset += copy;
+ }
+
+ for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+     int end;
+     skb_frag_t *f = &skb_shinfo(skb)->frags[i];
+
+     WARN_ON(start > offset + len);
+
+     end = start + skb_frag_size(f);
+     if ((copy = end - offset) > 0) {
+         u32 p_off, p_len, copied;
+         struct page *p;
+         u8 *vaddr;
+
+         if (copy > len)
+             copy = len;
+
+#if LINUX_VERSION_CODE > KERNEL_VERSION(4, 0, 0)
+         skb_frag_foreach_page(f,
+                       f->page_offset + offset - start,
+                       copy, p, p_off, p_len, copied) {
+             vaddr = kmap_atomic(p);
+             //memcpy(to + copied, vaddr + p_off, p_len);
+             __skb_change_bits(vaddr + p_off, p_len, idx);
+             kunmap_atomic(vaddr);
+         }
+#else
+         vaddr = kmap_atomic(skb_frag_page(f));
+         __skb_change_bits(vaddr + f->page_offset + offset - start, copy, idx);
+         kunmap_atomic(vaddr);
+#endif
+
+         if ((len -= copy) == 0)
+             return 0;
+         offset += copy;
+     }
+     start = end;
+ }
+
+ skb_walk_frags(skb, frag_iter) {
+     int end;
+
+     WARN_ON(start > offset + len);
+
+     end = start + frag_iter->len;
+     if ((copy = end - offset) > 0) {
+         if (copy > len)
+             copy = len;
+         if (skb_change_bits(frag_iter, offset - start, copy, idx))
+             goto fault;
+         if ((len -= copy) == 0)
+             return 0;
+         offset += copy;
+     }
+     start = end;
+ }
+
+ if (!len)
+     return 0;
+
+fault:
+ return -EFAULT;
+}
+
+
 int digest_init(void)
 {
  int ret;
+ int i;
+ unsigned long int next = 1;
+ for (i = 0; i < 65536; i ++) {
+     next = next * 2 + 1; // TODO
+     MY_XOR[i] = next % 251;
+ }
 
  ret = digest_trace_init();
  if (ret) {
diff --git a/src/digest_core.h b/src/digest_core.h
index 007628c..3ba8c80 100644
--- a/src/digest_core.h
+++ b/src/digest_core.h
@@ -79,6 +79,8 @@ extern atomic_t digest_trace_head_num;
 extern atomic_t digest_trace_free_num;
 extern int digest_trace_log_total;
 
+extern int digest_xor;
+
 extern atomic64_t digest_current, digest_total1, digest_total2, digest_drop_total;
 extern atomic64_t digest_drop_connect;
 
diff --git a/src/digest_sysctl.c b/src/digest_sysctl.c
index 27adfa3..3bfe0ae 100644
--- a/src/digest_sysctl.c
+++ b/src/digest_sysctl.c
@@ -478,6 +478,13 @@ static struct ctl_table digest_sysctl_table[] = {
      .mode = 0644,
      .proc_handler = digest_trace_show_handler,
  },
+ {
+     .procname = "digest_xor",
+     .data = &digest_xor,
+     .maxlen = sizeof(int),
+     .mode = 0644,
+     .proc_handler = proc_dointvec
+ },
  {}
 };