net: Add frag_list support to skb_segment

This patch adds limited support for handling frag_list packets in
skb_segment.  The intention is to support GRO (Generic Receive Offload)
packets which will be constructed by chaining normal packets using
frag_list.

As such we require all frag_list members terminate on exact MSS
boundaries.  This is checked using BUG_ON.

As there should only be one producer in the kernel of such packets,
namely GRO, this requirement should not be difficult to maintain.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 59 insertions, 14 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index b1f628741f4c..18e224af05a6 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2428,6 +2428,7 @@ struct sk_buff *skb_segment(struct sk_buff *skb, int features)
 {
         struct sk_buff *segs = NULL;
         struct sk_buff *tail = NULL;
+        struct sk_buff *fskb = skb_shinfo(skb)->frag_list;
         unsigned int mss = skb_shinfo(skb)->gso_size;
         unsigned int doffset = skb->data - skb_mac_header(skb);
         unsigned int offset = doffset;
@@ -2447,7 +2448,6 @@ struct sk_buff *skb_segment(struct sk_buff *skb, int features)
                 struct sk_buff *nskb;
                 skb_frag_t *frag;
                 int hsize;
-                int k;
                 int size;
 
                 len = skb->len - offset;
@@ -2460,9 +2460,36 @@ struct sk_buff *skb_segment(struct sk_buff *skb, int features)
                 if (hsize > len || !sg)
                         hsize = len;
 
-                nskb = alloc_skb(hsize + doffset + headroom, GFP_ATOMIC);
-                if (unlikely(!nskb))
-                        goto err;
+                if (!hsize && i >= nfrags) {
+                        BUG_ON(fskb->len != len);
+
+                        pos += len;
+                        nskb = skb_clone(fskb, GFP_ATOMIC);
+                        fskb = fskb->next;
+
+                        if (unlikely(!nskb))
+                                goto err;
+
+                        hsize = skb_end_pointer(nskb) - nskb->head;
+                        if (skb_cow_head(nskb, doffset + headroom)) {
+                                kfree_skb(nskb);
+                                goto err;
+                        }
+
+                        nskb->truesize += skb_end_pointer(nskb) - nskb->head -
+                                          hsize;
+                        skb_release_head_state(nskb);
+                        __skb_push(nskb, doffset);
+                } else {
+                        nskb = alloc_skb(hsize + doffset + headroom,
+                                         GFP_ATOMIC);
+
+                        if (unlikely(!nskb))
+                                goto err;
+
+                        skb_reserve(nskb, headroom);
+                        __skb_put(nskb, doffset);
+                }
 
                 if (segs)
                         tail->next = nskb;
@@ -2473,13 +2500,15 @@ struct sk_buff *skb_segment(struct sk_buff *skb, int features)
                 __copy_skb_header(nskb, skb);
                 nskb->mac_len = skb->mac_len;
 
-                skb_reserve(nskb, headroom);
                 skb_reset_mac_header(nskb);
                 skb_set_network_header(nskb, skb->mac_len);
                 nskb->transport_header = (nskb->network_header +
                                           skb_network_header_len(skb));
-                skb_copy_from_linear_data(skb, skb_put(nskb, doffset),
-                                          doffset);
+                skb_copy_from_linear_data(skb, nskb->data, doffset);
+
+                if (pos >= offset + len)
+                        continue;
+
                 if (!sg) {
                         nskb->ip_summed = CHECKSUM_NONE;
                         nskb->csum = skb_copy_and_csum_bits(skb, offset,
@@ -2489,14 +2518,11 @@ struct sk_buff *skb_segment(struct sk_buff *skb, int features)
                 }
 
                 frag = skb_shinfo(nskb)->frags;
-                k = 0;
 
                 skb_copy_from_linear_data_offset(skb, offset,
                                                  skb_put(nskb, hsize), hsize);
 
-                while (pos < offset + len) {
-                        BUG_ON(i >= nfrags);
-
+                while (pos < offset + len && i < nfrags) {
                         *frag = skb_shinfo(skb)->frags[i];
                         get_page(frag->page);
                         size = frag->size;
@@ -2506,20 +2532,39 @@ struct sk_buff *skb_segment(struct sk_buff *skb, int features)
                                 frag->size -= offset - pos;
                         }
 
-                        k++;
+                        skb_shinfo(nskb)->nr_frags++;
 
                         if (pos + size <= offset + len) {
                                 i++;
                                 pos += size;
                         } else {
                                 frag->size -= pos + size - (offset + len);
-                                break;
+                                goto skip_fraglist;
                         }
 
                         frag++;
                 }
 
-                skb_shinfo(nskb)->nr_frags = k;
+                if (pos < offset + len) {
+                        struct sk_buff *fskb2 = fskb;
+
+                        BUG_ON(pos + fskb->len != offset + len);
+
+                        pos += fskb->len;
+                        fskb = fskb->next;
+
+                        if (fskb2->next) {
+                                fskb2 = skb_clone(fskb2, GFP_ATOMIC);
+                                if (!fskb2)
+                                        goto err;
+                        } else
+                                skb_get(fskb2);
+
+                        BUG_ON(skb_shinfo(nskb)->frag_list);
+                        skb_shinfo(nskb)->frag_list = fskb2;
+                }
+
+skip_fraglist:
                 nskb->data_len = len - hsize;
                 nskb->len += nskb->data_len;
                 nskb->truesize += nskb->data_len;