linux-ext4 - [PATCH 1/6] ext4: sysfs: print ext4_super

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Message-Id: <20180620153322.54221-1-arnd@arndb.de>
Date:   Wed, 20 Jun 2018 17:32:58 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.com>
Cc:     y2038@...ts.linaro.org, linux-ext4@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>, stable@...r.kernel.org,
        Tyson Nottingham <tgnottingham@...il.com>,
        Riccardo Schirone <sirmy15@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/6] ext4: sysfs: print ext4_super_block fields as little-endian

While working on extended rand for last_error/first_error timestamps,
I noticed that the endianess is wrong, we access the little-endian
fields in struct ext4_super_block as native-endian when we print them.

This adds a special case in ext4_attr_show() and ext4_attr_store()
to byteswap the superblock fields if needed.

In older kernels, this code was part of super.c, it got moved to sysfs.c
in linux-4.4.

Cc: stable@...r.kernel.org
Fixes: 52c198c6820f ("ext4: add sysfs entry showing whether the fs contains errors")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 fs/ext4/sysfs.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index f34da0bb8f17..b970a200f20c 100644
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -274,8 +274,12 @@ static ssize_t ext4_attr_show(struct kobject *kobj,
 	case attr_pointer_ui:
 		if (!ptr)
 			return 0;
-		return snprintf(buf, PAGE_SIZE, "%u\n",
-				*((unsigned int *) ptr));
+		if (a->attr_ptr == ptr_ext4_super_block_offset)
+			return snprintf(buf, PAGE_SIZE, "%u\n",
+					le32_to_cpup(ptr));
+		else
+			return snprintf(buf, PAGE_SIZE, "%u\n",
+					*((unsigned int *) ptr));
 	case attr_pointer_atomic:
 		if (!ptr)
 			return 0;
@@ -308,7 +312,10 @@ static ssize_t ext4_attr_store(struct kobject *kobj,
 		ret = kstrtoul(skip_spaces(buf), 0, &t);
 		if (ret)
 			return ret;
-		*((unsigned int *) ptr) = t;
+		if (a->attr_ptr == ptr_ext4_super_block_offset)
+			*((__le32 *) ptr) = cpu_to_le32(t);
+		else
+			*((unsigned int *) ptr) = t;
 		return len;
 	case attr_inode_readahead:
 		return inode_readahead_blks_store(sbi, buf, len);
-- 
2.9.0