solos-pci: Increase headroom on received packets

A comment in include/linux/skbuff.h says that:

 * Various parts of the networking layer expect at least 32 bytes of
 * headroom, you should not reduce this.

This was demonstrated by a panic when handling fragmented IPv6 packets:
http://marc.info/?l=linux-netdev&m=144236093519172&w=2

It's not entirely clear if that comment is still valid — and if it is,
perhaps netif_rx() ought to be enforcing it with a warning.

But either way, it is rather stupid from a performance point of view
for us to be receiving packets into a buffer which doesn't have enough
room to prepend an Ethernet header — it means that *every* incoming
packet is going to be need to be reallocated. So let's fix that.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/atm/solos-pci.c b/drivers/atm/solos-pci.c
index 74e18b0a6d8945ac6df8537d394729354769e6da..3d7fb6516f74f83cd9276b4d5ff4d0a19d403241 100644 (file)
--- a/drivers/atm/solos-pci.c
+++ b/drivers/atm/solos-pci.c
@@ -805,7 +805,12 @@ static void solos_bh(unsigned long card_arg)
                                        continue;
                                }
 
-                               skb = alloc_skb(size + 1, GFP_ATOMIC);
+                               /* Use netdev_alloc_skb() because it adds NET_SKB_PAD of
+                                * headroom, and ensures we can route packets back out an
+                                * Ethernet interface (for example) without having to
+                                * reallocate. Adding NET_IP_ALIGN also ensures that both
+                                * PPPoATM and PPPoEoBR2684 packets end up aligned. */
+                               skb = netdev_alloc_skb_ip_align(NULL, size + 1);
                                if (!skb) {
                                        if (net_ratelimit())
                                                dev_warn(&card->dev->dev, "Failed to allocate sk_buff for RX\n");
@@ -869,7 +874,10 @@ static void solos_bh(unsigned long card_arg)
                /* Allocate RX skbs for any ports which need them */
                if (card->using_dma && card->atmdev[port] &&
                    !card->rx_skb[port]) {
-                       struct sk_buff *skb = alloc_skb(RX_DMA_SIZE, GFP_ATOMIC);
+                       /* Unlike the MMIO case (qv) we can't add NET_IP_ALIGN
+                        * here; the FPGA can only DMA to addresses which are
+                        * aligned to 4 bytes. */
+                       struct sk_buff *skb = dev_alloc_skb(RX_DMA_SIZE);
                        if (skb) {
                                SKB_CB(skb)->dma_addr =
                                        dma_map_single(&card->dev->dev, skb->data,