On Wed, 14 Mar 2018 12:01:19 +0100
Rafał Miłecki <[email protected]> wrote:

> diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c 
> b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c
> index 19048526b4af..db6987015fb1 100644
> --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c
> +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c
> @@ -230,6 +230,34 @@ static void brcmf_netdev_set_multicast_list(struct 
> net_device *ndev)
>       schedule_work(&ifp->multicast_work);
>  }
>  
> +/**
> + * brcmf_skb_is_iapp - checks if skb is an IAPP packet
> + *
> + * @skb: skb to check
> + */
> +static bool brcmf_skb_is_iapp(struct sk_buff *skb)
> +{
> +     const u8 iapp_l2_update_packet[6] __aligned(2) = {
> +             0x00, 0x01, 0xaf, 0x81, 0x01, 0x00,
> +     };
> +     unsigned char *eth_data = skb_mac_header(skb) + ETH_HLEN;
> +#if !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
> +     const u16 *a = (const u16 *)eth_data;
> +     const u16 *b = (const u16 *)iapp_l2_update_packet;
> +#endif
> +
> +     if (skb->len - skb->mac_len != 6 ||
> +         !is_multicast_ether_addr(eth_hdr(skb)->h_dest))
> +             return false;
> +
> +#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
> +     return !(((*(const u32 *)eth_data) ^ (*(const u32 
> *)iapp_l2_update_packet)) |
> +              ((*(const u16 *)(eth_data + 4)) ^ (*(const u16 
> *)(iapp_l2_update_packet + 4))));
> +#else
> +     return !((a[0] ^ b[0]) | (a[1] ^ b[1]) | (a[2] ^ b[2]));
> +#endif
> +}
> +
>  static netdev_tx_t brcmf_netdev_start_xmit(struct sk_buff *skb,
>                                          struct net_device *ndev)
>  {
> @@ -250,6 +278,12 @@ static netdev_tx_t brcmf_netdev_start_xmit(struct 
> sk_buff *skb,
>               goto done;
>       }
>  
> +     if (!IS_ENABLED(CONFIG_BRCMFMAC_IAPP) && brcmf_skb_is_iapp(skb)) {
> +             dev_kfree_skb(skb);
> +             ret = -EINVAL;
> +             goto done;
> +     }
> +

The usual way to handle config options in kernel is either inline
stub function or #define

#ifdef CONFIG_BRFMMAC_IAPP
static bool brcmf_skb_is_app(...) {
        real code
}
#else
#define brcmf_skb_is_app  (false)
#endif

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