linux-kernel - [RFC v2 4/5] md: introduce MAX_RAID_DISKS macro to replace magic number

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Message-Id: <20260203061259.609206-5-zhengqixing@huaweicloud.com>
Date: Tue,  3 Feb 2026 14:12:58 +0800
From: Zheng Qixing <zhengqixing@...weicloud.com>
To: song@...nel.org,
	yukuai@...as.com,
	linan122@...wei.com
Cc: xni@...hat.com,
	linux-raid@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	houtao1@...wei.com,
	zhengqixing@...wei.com
Subject: [RFC v2 4/5] md: introduce MAX_RAID_DISKS macro to replace magic number

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

Per-device state is stored as a __le16 dev_roles[] array (2 bytes per
device) plus a fixed 256-byte header, still within a 4 KiB superblock.
Therefore the theoretical maximum is (4096 - 256) / 2 = 1920 entries.

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 | 5 +++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index f319621c6832..aebbdbaa4e0a 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1873,7 +1873,7 @@ 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;
@@ -2050,7 +2050,7 @@ 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..14f9db38b7c5 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -21,6 +21,11 @@
 #include <linux/raid/md_u.h>
 #include <trace/events/block.h>
 
+/*
+ * v1.x superblock occupies one 4 KiB block: 256B header + 2B per device
+ * in dev_roles[].
+ */
+#define MAX_RAID_DISKS ((4096-256)/2)
 #define MaxSector (~(sector_t)0)
 
 enum md_submodule_type {
-- 
2.39.2