Man page 9 : skb_frag_dma_map

skb_frag_dma_map - maps a paged fragment via the DMA API

dma_addr_t skb_frag_dma_map(struct device *  dev , const skb_frag_t *  frag , size_t  offset , size_t  size , enum dma_data_direction  dir );

dev
    the device to map the fragment to

frag
    the paged fragment to map

offset
    the offset within the fragment (starting at the fragmentAqs own offset)

size
    the number of bytes to map

dir
    the direction of the mapping (PCI_DMA_*)

Maps the page associated with frag to device.