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

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Message-ID: <ca823522-fe78-4eb7-ae1d-b017d16e39fe@linux.dev>
Date: Mon, 29 Jul 2024 11:01:29 +0800
From: Youling Tang <youling.tang@...ux.dev>
To: Theodore Ts'o <tytso@....edu>
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 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