1. 根目录:
2. arch
3. ia64
4. kernel
5. dma-mapping.c

#include <linux/dma-mapping.h>
#include <linux/export.h>

/* Set this to 1 if there is a HW IOMMU in the system */
int iommu_detected __read_mostly;

struct dma_map_ops *dma_ops;
EXPORT_SYMBOL(dma_ops);

#define PREALLOC_DMA_DEBUG_ENTRIES (1 << 16)

static int __init dma_init(void)
{
	dma_debug_init(PREALLOC_DMA_DEBUG_ENTRIES);

	return 0;
}
fs_initcall(dma_init);

struct dma_map_ops *dma_get_ops(struct device *dev)
{
	return dma_ops;
}
EXPORT_SYMBOL(dma_get_ops);