Kernel Support for DAFS Servers

Special capabilities and requirements of networking transports used by DAFS servers expose a number of kernel design and structure issues. In general, a DAFS file server needs to be able to

1. Do asynchronous file I/O
2. Integrate network and disk I/O event delivery
3. Lock file buffers while RDMA is in progress
4. Avoid memory copies

In what follows we describe our proposals for new kernel support in the FreeBSD kernel. Work on implementing these proposals is currently in progress. Section 4.1 argues for kernel asynchronous file I/O interfaces presently lacking in FreeBSD, and integrating network and file event notification and delivery. Section 4.2 presents a vnode interface designed to address these needs. Section 4.3 examines kernel support for memory management of the asymmetric multiprocessor system that consists of the NIC and the host CPU. Finally, Section 4.4 argues for modifications to buffer cache locking and Section 4.5 outlines device driver requirements of memory-to-memory NIC.