https://github.com/ftrvxmtrx/c9
That one I wrote specifically for highly constrained environments. That's also the reason it has no memory allocation nor higher level API. Sorry, there are no examples that are open-source.
Hopefully someone will find it useful.

On Thu, Oct 13, 2016 at 6:29 PM, Stanley Lieber <sl@9front.org> wrote:
Steve Simon <steve@quintile.net> wrote:

>Hi all,
>
>I am using libtask on an embedded system with great success,
>however I would like to add remote file access to the system...
>
>9p seems a good fit ☺
>
>Anyone written or ported a small simple 9p library;
>I am after client and server but anything would be good.
>
>Thanks,
>
>-Steve

http://9p.cat-v.org/implementations

sl