Re: [PATCH RFC md-6.14] md: reintroduce md-linear

[Mike Snitzer <snitzer@kernel.org>]

On Thu, Jan 02, 2025 at 07:28:41PM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> THe md-linear is removed by commit 849d18e27be9 ("md: Remove deprecated
> CONFIG_MD_LINEAR") because it has been marked as deprecated for a long
> time.
> 
> However, md-linear is used widely for underlying disks with different size,
> sadly we didn't know this until now, and it's true useful to create
> partitions and assemble multiple raid and then append one to the other.
> 
> People have to use dm-linear in this case now, however, they will prefer
> to minimize the number of involved modules.
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

I agree with reinstating md-linear.  If/when we do remove md-linear
(again) we first need a seamless upgrade/conversion option (e.g. mdadm
updated to use dm-linear in the backend instead of md-linear).

This patch's header should probably also have this Fixes tag (unclear
if linux-stable would pick it up but it really is a regression given
there was no upgrade path offered to md-linear users):

Fixes: 849d18e27be9 md: Remove deprecated CONFIG_MD_LINEAR

Acked-by: Mike Snitzer <snitzer@kernel.org>