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

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Message-ID: <ZqJwa2-SsIf0aA_l@infradead.org>
Date: Thu, 25 Jul 2024 08:34:03 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: Christoph Hellwig <hch@...radead.org>,
	Youling Tang <youling.tang@...ux.dev>,
	Luis Chamberlain <mcgrof@...nel.org>, Chris Mason <clm@...com>,
	Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
	Theodore Ts'o <tytso@....edu>,
	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 Thu, Jul 25, 2024 at 05:30:58PM +0200, Arnd Bergmann wrote:
> Now I think we could just make the module_init() macro
> do the same thing as a built-in initcall() and put
> an entry in a special section, to let you have multiple
> entry points in a loadable module.
> 
> There are still at least two problems though:
> 
> - while link order is defined between files in a module,
>   I don't think there is any guarantee for the order between
>   two initcalls of the same level within a single file.

I think the sanest answer is to only allow one per file.  If you
are in the same file anyway calling one function from the other
is not a big burden.  It really is when they are spread over files
when it is annoying, and the three examples show that pretty
clearly.

> - For built-in code we don't have to worry about matching
>   the order of the exit calls since they don't exist there.
>   As I understand, the interesting part of this patch
>   series is about making sure the order matches between
>   init and exit, so there still needs to be a way to
>   express a pair of such calls.

That's why you want a single macro to define the init and exit
callbacks, so that the order can be matched up and so that
error unwinding can use the relative position easily.