mount nfs results in good authentication but "invalid argument" failure

[Sasha Z]

I'm trying to make an initrd for Arch Linux to support PXE booting.
When I boot the kernel and load the ramdisk, I need to mount the NFS
root and then do pivot_root. Unfortunately, I can't get the NFS mount
to work properly.

When I run the mount command on the client, it executes quietly with
no illuminating error messages, just a line that ends "...failed.
Invalid argument". I know it's able to contact the server since the
server logs indicate authentication success for the request.

This is on busybox 1.1.1. Behavior is the same on 1.01, so I assume
somewhere it's my fault. Thanks!