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

[RIc Wheeler <ricwheeler@gmail.com>]

On 1/7/25 12:24 PM, Mike Snitzer wrote:
> 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).


Agree with the need for an upgrade/conversion path.

>
> 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>
>