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

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Message-ID: <13a377d4-f647-436a-806e-c05413cef837@gmail.com>
Date: Tue, 7 Jan 2025 15:34:09 -0500
From: RIc Wheeler <ricwheeler@...il.com>
To: Mike Snitzer <snitzer@...nel.org>, Yu Kuai <yukuai1@...weicloud.com>
Cc: song@...nel.org, yukuai3@...wei.com, thetanix@...il.com, colyli@...e.de,
 linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
 yi.zhang@...wei.com, yangerkun@...wei.com, dm-devel@...ts.linux.dev,
 axboe@...nel.dk, linux-block@...r.kernel.org
Subject: Re: [PATCH RFC md-6.14] md: reintroduce md-linear


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@...wei.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@...wei.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@...nel.org>
>