Re: [PATCH 1/6] ext4: sysfs: print ext4_super_block fields as little-endian

On Thu, Jun 21, 2018 at 7:49 PM, Andreas Dilger [off-list ref] wrote:

On Jun 20, 2018, at 9:32 AM, Arnd Bergmann [off-list ref] wrote:

quoted

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@vger.kernel.org
Fixes: 52c198c6820f ("ext4: add sysfs entry showing whether the fs contains errors")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

I was wondering why this didn't just use le32_to_cpu() all the time,
but I see that these functions are being used for both ext4_super_block
(on-disk) fields, as well as ext4_sb_info (in-memory) fields.  A bit
ugly, but I don't think there is a better solution.

Reviewed-by: Andreas Dilger <redacted>

One alternative that I considered was to just do away with helpers
for the ext4_super_block structure and only use them for ext4_sb_info,
especially after the last patch that changes this again. However,
as a bugfix for stable backports it seemed best to keep the change
as simple as possible.

Thanks for the review,

      Arnd