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.woodho...@intel.com> --- diff --git a/drivers/atm/solos-pci.c b/drivers/atm/solos-pci.c index 74e18b0..3d7fb65 100644 --- 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, -- David Woodhouse Open Source Technology Centre david.woodho...@intel.com Intel Corporation
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