net: Export skb_zerocopy() to zerocopy from one skb to another

Make the skb zerocopy logic written for nfnetlink queue available for
use by other modules.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Reviewed-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jesse Gross <jesse@nicira.com>

1 files changed, 85 insertions, 0 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 2718fed53d8c..55859cb8b83d 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2122,6 +2122,91 @@ __wsum skb_copy_and_csum_bits(const struct sk_buff *skb, int offset,
 }
 EXPORT_SYMBOL(skb_copy_and_csum_bits);
 
+ /**
+ *      skb_zerocopy_headlen - Calculate headroom needed for skb_zerocopy()
+ *      @from: source buffer
+ *
+ *      Calculates the amount of linear headroom needed in the 'to' skb passed
+ *      into skb_zerocopy().
+ */
+unsigned int
+skb_zerocopy_headlen(const struct sk_buff *from)
+{
+        unsigned int hlen = 0;
+
+        if (!from->head_frag ||
+            skb_headlen(from) < L1_CACHE_BYTES ||
+            skb_shinfo(from)->nr_frags >= MAX_SKB_FRAGS)
+                hlen = skb_headlen(from);
+
+        if (skb_has_frag_list(from))
+                hlen = from->len;
+
+        return hlen;
+}
+EXPORT_SYMBOL_GPL(skb_zerocopy_headlen);
+
+/**
+ *      skb_zerocopy - Zero copy skb to skb
+ *      @to: destination buffer
+ *      @source: source buffer
+ *      @len: number of bytes to copy from source buffer
+ *      @hlen: size of linear headroom in destination buffer
+ *
+ *      Copies up to `len` bytes from `from` to `to` by creating references
+ *      to the frags in the source buffer.
+ *
+ *      The `hlen` as calculated by skb_zerocopy_headlen() specifies the
+ *      headroom in the `to` buffer.
+ */
+void
+skb_zerocopy(struct sk_buff *to, const struct sk_buff *from, int len, int hlen)
+{
+        int i, j = 0;
+        int plen = 0; /* length of skb->head fragment */
+        struct page *page;
+        unsigned int offset;
+
+        BUG_ON(!from->head_frag && !hlen);
+
+        /* dont bother with small payloads */
+        if (len <= skb_tailroom(to)) {
+                skb_copy_bits(from, 0, skb_put(to, len), len);
+                return;
+        }
+
+        if (hlen) {
+                skb_copy_bits(from, 0, skb_put(to, hlen), hlen);
+                len -= hlen;
+        } else {
+                plen = min_t(int, skb_headlen(from), len);
+                if (plen) {
+                        page = virt_to_head_page(from->head);
+                        offset = from->data - (unsigned char *)page_address(page);
+                        __skb_fill_page_desc(to, 0, page, offset, plen);
+                        get_page(page);
+                        j = 1;
+                        len -= plen;
+                }
+        }
+
+        to->truesize += len + plen;
+        to->len += len + plen;
+        to->data_len += len + plen;
+
+        for (i = 0; i < skb_shinfo(from)->nr_frags; i++) {
+                if (!len)
+                        break;
+                skb_shinfo(to)->frags[j] = skb_shinfo(from)->frags[i];
+                skb_shinfo(to)->frags[j].size = min_t(int, skb_shinfo(to)->frags[j].size, len);
+                len -= skb_shinfo(to)->frags[j].size;
+                skb_frag_ref(to, j);
+                j++;
+        }
+        skb_shinfo(to)->nr_frags = j;
+}
+EXPORT_SYMBOL_GPL(skb_zerocopy);
+
 void skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to)
 {
         __wsum csum;