linux-kernel - Re: [PATCH 6/7] lib: Give XOR_BLOCKS, RAID6

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Message-ID: <68e6ea973d318_2f89910066@dwillia2-mobl4.notmuch>
Date: Wed, 8 Oct 2025 15:49:59 -0700
From: <dan.j.williams@...el.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>,
	<linux-kernel@...r.kernel.org>
CC: <akpm@...ux-foundation.org>, Kent Overstreet <kent.overstreet@...ux.dev>,
	Eric Biggers <ebiggers@...nel.org>
Subject: Re: [PATCH 6/7] lib: Give XOR_BLOCKS, RAID6_PQ config opts names

Kent Overstreet wrote:
> Give these config options names so that they show up under the "Library
> routes" kernel configuration menu, and can be enabled by distributions.

A distribution specifies a kernel configuration. A distribution that
ships a given out-of-tree module can arrange for all its dependencies to
be met.

> These are needed for bcachefs to be built out of tree.
> 
> These libraries are both for RAID5/6.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Eric Biggers <ebiggers@...nel.org>
> Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev>
> ---
>  crypto/Kconfig | 2 +-
>  lib/Kconfig    | 4 +++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/crypto/Kconfig b/crypto/Kconfig
> index 23bd98981ae8..da4f072abae0 100644
> --- a/crypto/Kconfig
> +++ b/crypto/Kconfig
> @@ -3,7 +3,7 @@
>  # Generic algorithms support
>  #
>  config XOR_BLOCKS
> -	tristate
> +	tristate "Accelerated block xor algorithm"

For example, the approach taken with the CXL unit test modules in
tools/testing/ is to have them assert all their dependencies.
Specifically, tools/testing/cxl/config_check.c validates the test
environment rather than giving the out-of-tree module the ability to
select symbols.

Now in this specific case of XOR_BLOCKS, if a distribution really wants
CONFIG_XOR_BLOCKS=n in its main config *and* wants to ship an
out-of-tree module that depends on CONFIG_XOR_BLOCKS=m, then that
distribution needs to provide an xor.ko to meet that dependency. Not
make upstream carry a patch to make that symbol configurable with no
upstream consumer.

tools/testing/cxl/Kbuild is an example of building a set of in-tree
modules as out-of-tree modules.