linux-kernel - Re: [RFC PATCH 4/5] md: introduce MAX_RAID

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Message-ID: <26965.25787.328101.504732@quad.stoffel.home>
Date: Wed, 31 Dec 2025 13:00:27 -0500
From: "John Stoffel" <john@...ffel.org>
To: Zheng Qixing <zhengqixing@...weicloud.com>
Cc: song@...nel.org,
    yukuai@...as.com,
    linux-raid@...r.kernel.org,
    linux-kernel@...r.kernel.org,
    yi.zhang@...wei.com,
    yangerkun@...wei.com,
    houtao1@...wei.com,
    zhengqixing@...wei.com,
    linan122@...artners.com
Subject: Re: [RFC PATCH 4/5] md: introduce MAX_RAID_DISKS macro to replace magic number

>>>>> "Zheng" == Zheng Qixing <zhengqixing@...weicloud.com> writes:

> From: Zheng Qixing <zhengqixing@...wei.com>

> Define MAX_RAID_DISKS macro for the maximum number of RAID disks.
> No functional change.

> Signed-off-by: Zheng Qixing <zhengqixing@...wei.com>
> ---
>  drivers/md/md.c | 4 ++--
>  drivers/md/md.h | 1 +
>  2 files changed, 3 insertions(+), 2 deletions(-)

> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 9eeab5258189..d2f136706f6c 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -1888,7 +1888,7 @@ static int super_1_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor_
 
>  	if (sb->magic != cpu_to_le32(MD_SB_MAGIC) ||
sb-> major_version != cpu_to_le32(1) ||
> -	    le32_to_cpu(sb->max_dev) > (4096-256)/2 ||
> +	    le32_to_cpu(sb->max_dev) > MAX_RAID_DISKS ||
>  	    le64_to_cpu(sb->super_offset) != rdev->sb_start ||
>  	    (le32_to_cpu(sb->feature_map) & ~MD_FEATURE_ALL) != 0)
>  		return -EINVAL;
> @@ -2065,7 +2065,7 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *freshest, struc
mddev-> resync_offset = le64_to_cpu(sb->resync_offset);
>  		memcpy(mddev->uuid, sb->set_uuid, 16);
 
> -		mddev->max_disks =  (4096-256)/2;
> +		mddev->max_disks = MAX_RAID_DISKS;
 
>  		if (!mddev->logical_block_size)
mddev-> logical_block_size = le32_to_cpu(sb->logical_block_size);
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index a083f37374d0..6a4af4a1959c 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -22,6 +22,7 @@
>  #include <trace/events/block.h>
 
>  #define MaxSector (~(sector_t)0)
> +#define MAX_RAID_DISKS ((4096-256)/2)

Looks fine to me, except there's no explanation for the magic numbers
here.  Sure, it's 1916 devices max, but WHY?  Other than that nit,
looks fine.