linux-kernel - Re: [PATCH] Export MDRAID bitmap on disk structure in UAPI header file

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Message-ID: <20250203124326.66217544@mtkaczyk-private-dev>
Date: Mon, 3 Feb 2025 12:43:45 +0100
From: Mariusz Tkaczyk <mtkaczyk@...nel.org>
To: Tomas Mudrunka <tomas.mudrunka@...il.com>
Cc: Song Liu <song@...nel.org>, Yu Kuai <yukuai3@...wei.com>,
 linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Export MDRAID bitmap on disk structure in UAPI header
 file

On Tue, 31 Dec 2024 04:09:27 +0100
Tomas Mudrunka <tomas.mudrunka@...il.com> wrote:

> When working on software that manages MD RAID disks from
> userspace. Currently provided headers only contain MD superblock.
> That is not enough to fully populate MD RAID metadata.
> Therefore this patch adds bitmap superblock as well.
> 
> Signed-off-by: Tomas Mudrunka <tomas.mudrunka@...il.com>
> ---

Hello Tomas,
Jumping here again.. I tried to build mdadm against your patch.
In mdadm we used copied headers for years. I submitted PR for review:
This simple one to remove legacy ifdef:
https://github.com/md-raid-utilities/mdadm/pull/148

And this one to start using kernel provided headers:
https://github.com/md-raid-utilities/mdadm/pull/149

Going back to you change, to integrate it with mdadm well I need:
/* Notify that kernel provides it */
#define MD_BITMAP_SUBERBLOCK_EXPORTED 1 

Probably I can use any define to check it, but for clarity I would like
to keep clear differentiation. I hope it is not a problem.

And missing defines used by mdadm:

#define BITMAP_MAJOR_LO 3
/* version 4 insists the bitmap is in little-endian order
 * with version 3, it is host-endian which is non-portable
 */
#define BITMAP_MAJOR_HI 4
#define	BITMAP_MAJOR_CLUSTERED 5

see:
https://github.com/md-raid-utilities/mdadm/blob/main/bitmap.h


After that, I should be able to compile mdadm.

Thanks,
Mariusz