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

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Date:   Thu, 21 Jun 2018 22:07:14 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     "Theodore Ts'o" <tytso@....edu>, Jan Kara <jack@...e.com>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        "# 3.4.x" <stable@...r.kernel.org>,
        Tyson Nottingham <tgnottingham@...il.com>,
        Riccardo Schirone <sirmy15@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: 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 <adilger@...ger.ca> wrote:
> On Jun 20, 2018, at 9:32 AM, Arnd Bergmann <arnd@...db.de> wrote:
>>
>> 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>
>
> 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 <adilger@...ger.ca>

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