Open Source Linux DMA driver

Hi, I am new to FPGA use and seeking helpful advices.

Here is what I need on Linux:

Application needs to use the following interface to communicate with FPGA on PCIe:

fpga_processing(int fpga_channel, char *input_buf, int input_size, char *out_buf, int *output_size);

* fpga_channel: specify which fpga to use ( assuming there are multiple on board )

* input_buf stores raw data ( of size input_size) to be passed to FPGA

* FPGA stores processed data at output_buf, and returns its size to output_size

My question: are there any Linux DMA drivers ( preferably open source ones ) to accomplish this?

Thanks in advance for any info.