print-ext4_super_block-fields-as-little-endian

   1 ext4: sysfs: print ext4_super_block fields as little-endian
   2
   3 From: Arnd Bergmann <arnd@arndb.de>
   4
   5 While working on extended rand for last_error/first_error timestamps,
   6 I noticed that the endianess is wrong; we access the little-endian
   7 fields in struct ext4_super_block as native-endian when we print them.
   8
   9 This adds a special case in ext4_attr_show() and ext4_attr_store()
  10 to byteswap the superblock fields if needed.
  11
  12 In older kernels, this code was part of super.c, it got moved to
  13 sysfs.c in linux-4.4.
  14
  15 Cc: stable@vger.kernel.org
  16 Fixes: 52c198c6820f ("ext4: add sysfs entry showing whether the fs contains errors")
  17 Reviewed-by: Andreas Dilger <adilger@dilger.ca>
  18 Signed-off-by: Arnd Bergmann <arnd@arndb.de>
  19 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  20 ---
  21  fs/ext4/sysfs.c | 13 ++++++++++---
  22  1 file changed, 10 insertions(+), 3 deletions(-)
  23
  24 diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
  25 index f34da0bb8f17..b970a200f20c 100644
  26 --- a/fs/ext4/sysfs.c
  27 +++ b/fs/ext4/sysfs.c
  28 @@ -274,8 +274,12 @@ static ssize_t ext4_attr_show(struct kobject *kobj,
  29         case attr_pointer_ui:
  30                 if (!ptr)
  31                         return 0;
  32 -               return snprintf(buf, PAGE_SIZE, "%u\n",
  33 -                               *((unsigned int *) ptr));
  34 +               if (a->attr_ptr == ptr_ext4_super_block_offset)
  35 +                       return snprintf(buf, PAGE_SIZE, "%u\n",
  36 +                                       le32_to_cpup(ptr));
  37 +               else
  38 +                       return snprintf(buf, PAGE_SIZE, "%u\n",
  39 +                                       *((unsigned int *) ptr));
  40         case attr_pointer_atomic:
  41                 if (!ptr)
  42                         return 0;
  43 @@ -308,7 +312,10 @@ static ssize_t ext4_attr_store(struct kobject *kobj,
  44                 ret = kstrtoul(skip_spaces(buf), 0, &t);
  45                 if (ret)
  46                         return ret;
  47 -               *((unsigned int *) ptr) = t;
  48 +               if (a->attr_ptr == ptr_ext4_super_block_offset)
  49 +                       *((__le32 *) ptr) = cpu_to_le32(t);
  50 +               else
  51 +                       *((unsigned int *) ptr) = t;
  52                 return len;
  53         case attr_inode_readahead:
  54                 return inode_readahead_blks_store(sbi, buf, len);
  55 --
  56 2.9.0
  57
  58