linux-kernel - [PATCH] btrfs: avoid opencoded 64-bit div/mod operation

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Message-Id: <20241216083248.1816638-1-arnd@kernel.org>
Date: Mon, 16 Dec 2024 09:32:37 +0100
From: Arnd Bergmann <arnd@...nel.org>
To: Chris Mason <clm@...com>,
	Josef Bacik <josef@...icpanda.com>,
	David Sterba <dsterba@...e.com>,
	Anand Jain <anand.jain@...cle.com>
Cc: Arnd Bergmann <arnd@...db.de>,
	Qu Wenruo <wqu@...e.com>,
	Johannes Thumshirn <johannes.thumshirn@....com>,
	Boris Burkov <boris@....io>,
	Naohiro Aota <naohiro.aota@....com>,
	linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] btrfs: avoid opencoded 64-bit div/mod operation

From: Arnd Bergmann <arnd@...db.de>

Dividing 64-bit numbers causes a link failure on 32-bit builds:

arm-linux-gnueabi-ld: fs/btrfs/sysfs.o: in function `btrfs_read_policy_store':
sysfs.c:(.text+0x3ce0): undefined reference to `__aeabi_ldivmod'

Use an explicit call to div_u64_rem() here to work around this. It would
be possible to optimize this further, but this is not a performance
critical operation.

Fixes: 185fa5c7ac5a ("btrfs: introduce RAID1 round-robin read balancing")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 fs/btrfs/sysfs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 50bc4b6cb821..67bc8fa4d6ab 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -1433,7 +1433,9 @@ static ssize_t btrfs_read_policy_store(struct kobject *kobj,
 #ifdef CONFIG_BTRFS_EXPERIMENTAL
 	if (index == BTRFS_READ_POLICY_RR) {
 		if (value != -1) {
-			if ((value % fs_devices->fs_info->sectorsize) != 0) {
+			u32 rem;
+			div_u64_rem(value, fs_devices->fs_info->sectorsize, &rem);
+			if (rem) {
 				btrfs_err(fs_devices->fs_info,
 "read_policy: min_contiguous_read %lld should be multiples of the sectorsize %u",
 					  value, fs_devices->fs_info->sectorsize);
-- 
2.39.5