Booting plan9 with ocaml

Community
1

Hey y’all :man_raising_hand:

Here’s some of the components involved in booting a plan9 system:

COMPONENT                SOURCE CODE                  MAN PAGE
--------------------------------------------------------------
kernel
/boot/boot               # /sys/src/9/boot/boot.c     boot(8)
/sys/src/9/boot/bootrc   # rc script                  boot(8)
/$cputype/init           # /sys/src/cmd/init.c        init(8)
/rc/bin/cpurc            # rc script                  cpurc(8)

On a terminal, /rc/bin/termrc would be used instead of /rc/bin/cpurc.

cpurc is an rc shell script:

Here’s an experimental conversion of this to ocaml:

As you can see, boot_cpu_main.ml simply calls out to different modules.

These modules can be found here:

This conversion from rc to ocaml is an early first pass.
A fairly naive approach has been taken.
There is lots of room for improvement.

Making some of these modules more idiomatic would likely require building plan9-specific libraries, instead of working with the portable OS libraries offered by the ocaml.

As you browse each of the modules used by boot_cpu_main.ml,
a convention you’ll notice is that the original rc code
is at the top of the file in a comment.
This makes it straighforward to compare the rc and ocaml code.

Here’s boot_factotum.ml for example:

(* Stock cpurc lines 21-22 and termrc lines 22-23 from the tracked baselines:

   mount /srv/factotum /mnt/factotum factotum
   bind -q /mnt/factotum/factotum /mnt/factotum
*)

let run () =
  Mount.mount ~flags:[]
    ~service:"/srv/factotum"
    ~old_name:"/mnt/factotum"
    ~spec:"factotum" ();
  Bind.bind ~flags:[ "-q" ]
    ~new_name:"/mnt/factotum/factotum"
    ~old_name:"/mnt/factotum"

The code works in that I have booted plan9 with it (boot_cpu_main.ml) and the system is apparently usable.

This is currently intended as an exploratory proof-of-concept.
A sort of experiment in what it’s like to use ocaml on plan9 instead of rc.

Here’s a post about the port of ocaml to plan9 that was used for this experiment:

Ed

7 Likes
2

Hi,

Can you give more context about what cpurc is? I think most of the people in the OCaml community are not familar with Plan 9 so this is a bit confusing. Have you written a kernel in OCaml? Are you mixing code with the Plan 9 kernel? Just a quick introduction and context would help.

1 Like
3

Is plan9 used in production anywhere? To do what? Really plan9 or inferno?

4

given the author linked to the 9front sources above, most likely 9front