I read the following from ibverbs’ website:

“InfiniBand host channel adapters (HCAs) and iWARP NICs commonly support direct hardware access from userspace (kernel bypass), and libibverbs supports this when available.”

To me, it sounds like user level processes can interact directly with the NIC bypassing the kernel level device driver and kernel as a whole after initial set up? If so, how is it done? Are certain memory registers of the NICs mapped into user space so the user level process can write to those memory location to trigger action of the NIC?

In general, after initial setup, system call isn’t needed to triger a simple RDMA send and recv right?