LibTLP is a software implementation of the PCIe transaction layer. It provides a well-abstracted DMA API shown below for issuing DMAs from software to hardware through a NetTLP adpater.
ssize_t dma_read(struct nettlp *nt, uintptr_t addr, void *buf, size_t count);
ssize_t dma_write(struct nettlp *nt, uintptr_t addr, void *buf, size_t count);Documents about NetTLP including LibTLP are in http://haeena.dev/nettlp