Why is Linux NFS server implemented in the kernel as opposed to userspace?

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http://unix.stackexchange.com – I was just wondering why the Linux NFS server is implemented in the kernel as opposed to a userspace application? I know a userspace NFS daemon exists, but it's not the standard method for providing NFS server services. I would think that running NFS server as a userspace application would be the preferred approach as it can provide added security having a daemon run in userspace instead of the kernel. It also would fit with the common Linux principal of doing one thing and doing it well (and that daemons shouldn't be a job for the kernel). In fact the only benefit I can think of running in (HowTos)