linux-ext4 - Re: [PATCH 1/4] module: Add module_subinit{_noexit} and module

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Message-ID: <20240729024412.GD377174@mit.edu>
Date: Sun, 28 Jul 2024 22:44:12 -0400
From: "Theodore Ts'o" <tytso@....edu>
To: Youling Tang <youling.tang@...ux.dev>
Cc: Christoph Hellwig <hch@...radead.org>, David Sterba <dsterba@...e.cz>,
        Arnd Bergmann <arnd@...db.de>, kreijack@...ind.it,
        Luis Chamberlain <mcgrof@...nel.org>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>, linux-kernel@...r.kernel.org,
        linux-modules@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        Youling Tang <tangyouling@...inos.cn>
Subject: Re: [PATCH 1/4] module: Add module_subinit{_noexit} and
 module_subeixt helper macros

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