Re: [PATCH 1/4] module: Add module_subinit{_noexit} and module_subeixt helper macros

Theodore Ts'o
2024-07-29T02:48:04Z

On Mon, Jul 29, 2024 at 09:46:17AM +0800, Youling Tang wrote:
> 1. Previous version implementation: array mode (see link 1) :
>    Advantages:
>    - Few changes, simple principle, easy to understand code.
>    Disadvantages:
>    - Each modified module needs to maintain an array, more code.
>
> 2. Current implementation: explicit call subinit in initcall (see link 2) :
>    Advantages:
>    - Direct use of helpes macros, the subinit call sequence is
>      intuitive, and the implementation is relatively simple.
>    Disadvantages:
>    - helper macros need to be implemented compared to array mode.
>
> 3. Only one module_subinit per file (not implemented, see link 3) :
>    Advantage:
>    - No need to display to call subinit.
>    Disadvantages:
>    - Magic order based on Makefile makes code more fragile,
>    - Make sure that each file has only one module_subinit,
>    - It is not intuitive to know which subinits the module needs
>      and in what order (grep and Makefile are required),
>    - With multiple subinits per module, it would be difficult to
>      define module_{subinit, subexit} by MODULE, and difficult to
>      rollback when initialization fails (I haven't found a good way
>      to do this yet).
>
>
> Personally, I prefer the implementation of method two.

But there's also method zero --- keep things the way they are, and
don't try to add a new astraction.

Advantage:

-- Code has worked for decades, so it is very well tested
-- Very easy to understand and maintain

Disadvantage

--- A few extra lines of C code.

which we need to weigh against the other choices.

- Ted