NFS addon needs updated to NFS v3

[kallisti5]

The NFS add-on (src/add-ons/kernel/file_systems/nfs) supports NFS v2 only. We should investigate upgrading the NFS v2 support to include NFS v3.

Changes in NFS v3:

• Addition of READDIR_PLUS operation. Allows faster read of directories, and reads of files > 2GiB

Mounting an NFS filesystem with files over 2GiB results in an overflow negitive size.

More information:

• ​https://www.linux-nfs.org/wiki/index.php/Readdir_NFSv3_With_Readdir_Plus
• ​https://www.freesoft.org/CIE/RFC/1813/37.htm

[kallisti5]

Example of > 2GiB overflow

[pulkomandy]

There is an entirely separate NFS v4 add-on, is that not enough?

The old NFS v2 add-on has unclear license (it was originally for BeOS and the original author didn't specify a license) so it isn't clear if we are even allowed to distribute it (see #1061).

We should clarify that before we make any more changes to this code, I think.