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

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Message-ID: <CAPhsuW5F94zauhvMd79VX0=JsFAY6S-0FJTK6Aqsr++UaDfy_g@mail.gmail.com>
Date: Tue, 7 Jan 2025 15:09:00 -0800
From: Song Liu <song@...nel.org>
To: RIc Wheeler <ricwheeler@...il.com>
Cc: Mike Snitzer <snitzer@...nel.org>, Yu Kuai <yukuai1@...weicloud.com>, 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 Tue, Jan 7, 2025 at 12:34 PM RIc Wheeler <ricwheeler@...il.com> wrote:
>
>
> 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>

Thanks all for feedback on this move. I agree that reinstating
md-linear is the right move for now.

Yu Kuai,

It appears to me that the path doesn't apply cleanly on the md-6.14
branch:

Applying: md: reintroduce md-linear
error: patch failed: drivers/md/Makefile:29
error: drivers/md/Makefile: patch does not apply
Patch failed at 0001 md: reintroduce md-linear
hint: Use 'git am --show-current-patch=diff' to see the failed patch
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

Please rebase and resend the patch.

Thanks,
Song