NFSv4 boot support?

[Ahmad Fatoum]

Hello Dan,

On 31.01.24 22:03, Dan Shelton wrote:
> Hello!
> 
> Does barebox support booting from a NFSv4 filesystem, e.g. boot from
> NFSv4 filesystem into a Linux NFSv4 netroot (diskless machine)?

The barebox network stack only does UDP/IP. There have been attempts to
bring a TCP stack into barebox, but none have so far succeeded to
make it mainline. This is a hard requirement before we can consider
supporting NFSv4. I hope that lwIP could fill this gap in the future,
but no one is actively continuing this work as far as I am aware[1].

> We need NFSv4, because it does not need rpcbind, and combines
> filesystem, lockd and other stuff all in one TCP port (2049). Site
> policy also does not allow NFSv2/NFSv3, but allows NFSv4.

Please note that this only concerns barebox and that kernel nfsroot is
unaffected. You can load kernel and device tree over TFTP and supply a
suitable command line argument to the kernel to use a NFS root.

The standard net boot target does just that:
https://elixir.bootlin.com/barebox/v2024.01.0/source/defaultenv/defaultenv-2-base/boot/net

It specifies TCP, but hardcodes v3 currently. I guess we could drop the v3 and let
the kernel decide on its own what version it will use? If that doesn't work, you can
override the file locally in your environment, e.g. via CONFIG_DEFAULT_ENVIRONMENT
pointing at a directory that contains a boot/net file with the appropriate
changes (or just call your boot target something else like boot/nfsv4).

Hope this helps.

[1]: Some attempts I am aware of:
     https://github.com/a3f/barebox/tree/lwip
     https://github.com/olerem/barebox/tree/picotcp-2019.06.29
     https://github.com/jmaselbas/barebox/commit/4a987bfdc2ad50c13126dd6290d2477c3fc0c87d

Cheers,
Ahmad

> 
> Dan

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