On Jun 20, 2018, at 9:32 AM, Arnd Bergmann <arnd@xxxxxxxx> 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@xxxxxxxxxxxxxxx
> Fixes: 52c198c6820f ("ext4: add sysfs entry showing whether the fs contains errors")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
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@xxxxxxxxx>
> ---
> 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
>
Cheers, Andreas
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