Re: [PATCH v2 0/6] fs: Add 9P filesystem support over virtio

[Kuan-Wei Chiu <visitorckw@gmail.com>]

Hi Peter,

On Sun, Aug 30, 2026 at 11:41:48AM +0100, Peter Robinson wrote:
> Hi Kuan-Wei,
> 
> > Add 9P network filesystem support to U-Boot.
> >
> > It allows U-Boot to directly mount host directories in virtualization
> > environments via virtio.
> 
> It would be useful to give an overview in the cover letter how/where
> you expect to be used. While new features are always welcome they also
> come with a maintenance burden so some background is always useful to
> provide more information.

The use case is loading images directly from the host into the VM. That
way I don't need to rebuild and repack disk images like ext4 every time
I modify the kernel, and I also don't have to bother setting up a TFTP
server.

I got the idea a while ago while browsing the upstream LK code and
noticed it had 9P support. I thought it would be cool to have something
similar in U-Boot for kernel loading and testing in qemu.

I will add this background to the cover letter if a v3 is needed.

> 
> From a network stack PoV does this work, been tested, with both the
> legacy stack and LWIP stack? I would tend to push this towards working
> with the LWIP stack as we're moving towards that being the default for
> standard U-Boot (not in SPL) and I wouldn't expect 9P to be supported
> in SPL.
> 
I have only implemented and tested 9P over virtio, so it uses
virtqueues and doesn't go through the network stack at all. It's
independent of both legacy and LWIP stacks. I am not sure if anyone
would actually want 9P over TCP in U-Boot, but if there is demand for
it, I can look into adding a transport driver over the network stack.

Regards,
Kuan-Wei