Arend van Spriel <arend.vanspriel@xxxxxxxxxxxx> writes: > On 3/14/2018 5:10 PM, Kalle Valo wrote: >> Rafał Miłecki <rafal@xxxxxxxxxx> writes: >> >>>>> + unsigned char *eth_data = skb_mac_header(skb) + ETH_HLEN; >>>>> +#if !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) >>>> >>>> #ifndef? >>> >>> I followed what is used in the include/linux/etherdevice.h. Is that a >>> good exceuse? Could it be there any some good reason for #if defined()? >> >> Don't know, maybe just a matter of taste? But it would be nice to know >> the background behind #ifdef vs #if defined(), never figured it out why >> two different forms. > > Well. In this case you could use either one, but if you have more > conditions #if defined() is bit more efficient: > > #ifdef A > #ifdef B > #endif > #endif > > vs. > > #if defined(A) && defined(B) Oh yeah, here defined() definitely helps. -- Kalle Valo
