1. 根目录:
2. net
3. core
4. kmap_skb.h

#include <linux/highmem.h>

static inline void *kmap_skb_frag(const skb_frag_t *frag)
{
#ifdef CONFIG_HIGHMEM
	BUG_ON(in_irq());

	local_bh_disable();
#endif
	return kmap_atomic(skb_frag_page(frag));
}

static inline void kunmap_skb_frag(void *vaddr)
{
	kunmap_atomic(vaddr);
#ifdef CONFIG_HIGHMEM
	local_bh_enable();
#endif
}