+/* We copy the packet for XDP in the following cases:
+ *
+ * 1) Packet is scattered across multiple rx buffers.
+ * 2) Headroom space is insufficient.
+ *
+ * This is inefficient but it's a temporary condition that
+ * we hit right after XDP is enabled and until queue is refilled
+ * with large buffers with sufficient headroom - so it should affect
+ * at most queue size packets.
+ * Afterwards, the conditions to enable
+ * XDP should preclude the underlying device from sending packets
+ * across multiple buffers (num_buf > 1), and we make sure buffers
+ * have enough headroom.
+ */
+static struct page *xdp_linearize_page(struct receive_queue *rq,
+ u16 *num_buf,
+ struct page *p,
+ int offset,
+ int page_off,
+ unsigned int *len)
+{
+ struct page *page = alloc_page(GFP_ATOMIC);
+
+ if (!page)
+ return NULL;
+
+ memcpy(page_address(page) + page_off, page_address(p) + offset, *len);
+ page_off += *len;
+
+ while (--*num_buf) {
+ unsigned int buflen;
+ void *buf;
+ int off;
+
+ buf = virtqueue_get_buf(rq->vq, &buflen);
+ if (unlikely(!buf))
+ goto err_buf;
+
+ p = virt_to_head_page(buf);
+ off = buf - page_address(p);
+
+ /* guard against a misconfigured or uncooperative backend that
+ * is sending packet larger than the MTU.
+ */
+ if ((page_off + buflen) > PAGE_SIZE) {
+ put_page(p);
+ goto err_buf;
+ }
+
+ memcpy(page_address(page) + page_off,
+ page_address(p) + off, buflen);
+ page_off += buflen;
+ put_page(p);
+ }
+
+ /* Headroom does not contribute to packet length */
+ *len = page_off - VIRTIO_XDP_HEADROOM;
+ return page;
+err_buf:
+ __free_pages(page, 0);
+ return NULL;
+}
+