+/* prepad is the amount to reserve at front. len is length after that.
+ * linear is a hint as to how much to copy (usually headers). */
+static struct sk_buff *tun_alloc_skb(size_t prepad, size_t len, size_t linear,
+ gfp_t gfp)
+{
+ struct sk_buff *skb;
+ unsigned int i;
+
+ skb = alloc_skb(prepad + len, gfp|__GFP_NOWARN);
+ if (skb) {
+ skb_reserve(skb, prepad);
+ skb_put(skb, len);
+ return skb;
+ }
+
+ /* Under a page? Don't bother with paged skb. */
+ if (prepad + len < PAGE_SIZE)
+ return NULL;
+
+ /* Start with a normal skb, and add pages. */
+ skb = alloc_skb(prepad + linear, gfp);
+ if (!skb)
+ return NULL;
+
+ skb_reserve(skb, prepad);
+ skb_put(skb, linear);
+
+ len -= linear;
+
+ for (i = 0; i < MAX_SKB_FRAGS; i++) {
+ skb_frag_t *f = &skb_shinfo(skb)->frags[i];
+
+ f->page = alloc_page(gfp|__GFP_ZERO);
+ if (!f->page)
+ break;
+
+ f->page_offset = 0;
+ f->size = PAGE_SIZE;
+
+ skb->data_len += PAGE_SIZE;
+ skb->len += PAGE_SIZE;
+ skb->truesize += PAGE_SIZE;
+ skb_shinfo(skb)->nr_frags++;
+
+ if (len < PAGE_SIZE) {
+ len = 0;
+ break;
+ }
+ len -= PAGE_SIZE;
+ }
+
+ /* Too large, or alloc fail? */
+ if (unlikely(len)) {
+ kfree_skb(skb);
+ skb = NULL;
+ }
+
+ return skb;
+}
+