af_iucv: use paged SKBs for big inbound messages

When an inbound message is bigger than a page, allocate a paged SKB,
and subsequently use IUCV receive primitive with IPBUFLST flag.
This relaxes the pressure to allocate big contiguous kernel buffers.

Signed-off-by: Eugene Crosser <[e-mail]>
Signed-off-by: Ursula Braun <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/iucv/af_iucv.c

···
 	return err;
 }
 
+static struct sk_buff *alloc_iucv_recv_skb(unsigned long len)
+{
+	size_t headroom, linear;
+	struct sk_buff *skb;
+	int err;
+
+	if (len < PAGE_SIZE) {
+		headroom = 0;
+		linear = len;
+	} else {
+		headroom = sizeof(struct iucv_array) * (MAX_SKB_FRAGS + 1);
+		linear = PAGE_SIZE - headroom;
+	}
+	skb = alloc_skb_with_frags(headroom + linear, len - linear,
+				   0, &err, GFP_ATOMIC | GFP_DMA);
+	WARN_ONCE(!skb,
+		  "alloc of recv iucv skb len=%lu failed with errcode=%d\n",
+		  len, err);
+	if (skb) {
+		if (headroom)
+			skb_reserve(skb, headroom);
+		skb_put(skb, linear);
+		skb->len = len;
+		skb->data_len = len - linear;
+	}
+	return skb;
+}
+
 /* iucv_process_message() - Receive a single outstanding IUCV message
  *
  * Locking: must be called with message_q.lock held
···
 			skb->len = 0;
 		}
 	} else {
-		rc = pr_iucv->message_receive(path, msg,
+		if (skb_is_nonlinear(skb)) {
+			struct iucv_array *iba = (struct iucv_array *)skb->head;
+			int i;
+
+			iba[0].address = (u32)(addr_t)skb->data;
+			iba[0].length = (u32)skb_headlen(skb);
+			for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+				skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+
+				iba[i + 1].address =
+					(u32)(addr_t)skb_frag_address(frag);
+				iba[i + 1].length = (u32)skb_frag_size(frag);
+			}
+			rc = pr_iucv->message_receive(path, msg,
+					      IUCV_IPBUFLST,
+					      (void *)iba, len, NULL);
+		} else {
+			rc = pr_iucv->message_receive(path, msg,
 					      msg->flags & IUCV_IPRMDATA,
 					      skb->data, len, NULL);
+		}
 		if (rc) {
 			kfree_skb(skb);
 			return;
 		}
-		skb_reset_transport_header(skb);
-		skb_reset_network_header(skb);
-		skb->len = len;
+		WARN_ON_ONCE(skb->len != len);
 	}
 
 	IUCV_SKB_CB(skb)->offset = 0;
···
 	struct sock_msg_q *p, *n;
 
 	list_for_each_entry_safe(p, n, &iucv->message_q.list, list) {
-		skb = alloc_skb(iucv_msg_length(&p->msg), GFP_ATOMIC | GFP_DMA);
+		skb = alloc_iucv_recv_skb(iucv_msg_length(&p->msg));
 		if (!skb)
 			break;
 		iucv_process_message(sk, skb, p->path, &p->msg);
···
 	if (len > sk->sk_rcvbuf)
 		goto save_message;
 
-	skb = alloc_skb(iucv_msg_length(msg), GFP_ATOMIC | GFP_DMA);
+	skb = alloc_iucv_recv_skb(iucv_msg_length(msg));
 	if (!skb)
 		goto save_message;