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

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Message-ID: <ZqOs84hdYkSV_YWd@infradead.org>
Date: Fri, 26 Jul 2024 07:04:35 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Youling Tang <youling.tang@...ux.dev>
Cc: Christoph Hellwig <hch@...radead.org>, kreijack@...ind.it,
	Arnd Bergmann <arnd@...db.de>, 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 Fri, Jul 26, 2024 at 04:54:59PM +0800, Youling Tang wrote:
> Based on this patch, we may need to do these things with this
>
>
> 1. Change the order of *.o in the Makefile (the same order as before the
> change)

While we'll need to be careful, we don't need to match the exact
order.  Most of the calls simply create slab caches / mempools and
similar things and the order for those does not matter at all.

Of course the register_filesytem calls need to be last, and sysfs
registration probably should be second to last, but for the vast
amount of calls the order does not matter as long as it is unwound
in reverse order.

> 2. We need to define module_subinit through the ifdef MODULE
> distinction,

Yes.

> When one of the subinit runs in a module fails, it is difficult
> to rollback execution of subexit.

By having both section in the same order, you an just walk the
exit section backwards from the offset that failed.  Of course that
only matters for the modular case as normal initcalls don't get
unwound when built-in either.

> 4. The order in which subinit is called is not intuitively known
> (although it can be found in the Makefile).

Link order through make file is already a well known concept due to
it mattering for built-in code.