A B0 driver like b0
or d0
is an executable that provides a service on the definitions of a B0 file. This manual shows how to develop a custom driver for B0 files.
The B0 file needs to be compiled and made accessible to the driver executable. At the moment the OCaml Dynlink
API is not being used. Instead the driver executable relinks its objects with a compilation of the B0 file to produce another executable that is executed to run the driver on the definitions.
With the help of the B0_driver
module this all happens transparently in the .drivers
directory of the _b0
directory.
For your driver to access a B0 file you need to create an OCaml library which has all the objects of your driver and registers its main
function by calling B0_driver.set
.
Source wise a typical driver source structure is:
src/mydriver_main.ml
src/mydriver_main_run.ml
The mydriver_main.ml
file implements and registers the driver. It's compiled object should be part of your driver library. Here's a minimal example :
open B0_std
open Cmdliner
let driver =
let name = "mydriver" and version = "v0.0.2-12-g2e7fa30e" in
let libs = ["mydriver" (* other needed libraries can be added here *) ] in
B0_driver.create ~name ~version ~libs
let my_driver conf = Fmt.pr "Running %s!@."; B0_driver.Exit.ok
let my_driver =
let doc = "My driver" in
let sdocs = Manpage.s_common_options in
let exits = B0_driver.Exit.Info.base_cmd in
let man = [ `S Manpage.s_description; "$(mname) does not much." ] in
B0_driver.with_b0_file ~driver (Term.const unit_cmd),
Term.info "mydriver" ~version:"v0.0.2-12-g2e7fa30e" ~doc ~sdocs ~exits ~man
let main () = Term.eval mydriver
let () = B0_driver.set driver ~main
The mydriver_main_run.ml
file defines your driver executable when it has no B0 file linked in. It's the program that runs your driver without the B0 file linked in. It should simply be:
let () =
let module D = Mydriver_main (* make sure we link it *) in
if !Sys.interactive then () else B0_driver.run ~has_b0_file:false
A few things to note:
OCAMLPATH
under the name you gave in to B0_driver
.#require
directive.The driver dance seems to be a bit slow for now. Even for the up-to-date dance we get into the 43ms b0 unit list
. But there's room for improvement. Here are different things to consider that could be done.
Dylink
once it gets lib support, but then what about platforms that don't support it.b0 file log --stats
and b0 -v -v
don't add up to what time b0
reports. Investigate, is it the execv ? June 2020: maybe it is/was that. Also see how much toplevel init takes (how ?).