kfifo_dma_out_prepare - setup a scatterlist for DMA output
kfifo_dma_out_prepare(fifo, sgl, nents, len);
This macro fills a scatterlist for DMA output which at most len bytes to transfer. It returns the number entries in the scatterlist array. A zero means there is no space available and the scatterlist is not filled.
Note that with only one concurrent reader and one concurrent writer, you don't need extra locking to use these macros.
|January 2017||Kernel Hackers Manual 4.8.|