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

Youling Tang
2024-07-29T03:02:00Z

On 29/07/2024 10:44, Theodore Ts'o wrote:
> 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.
The number of lines of code is not important, the main point is to
better ensure that subexit runs in the reverse order of subinit when
init fails.

Thanks,
Youling.

>
> which we need to weigh against the other choices.
>
> - Ted