Re: [PATCH v2 5/6] exfat: introduce exfat_chain_advance helper

[Chi Zhiling <chizhiling@163.com>]

On 4/3/26 10:34 AM, Yuezhang.Mo@sony.com wrote:
>> From: Chi Zhiling <chizhiling@kylinos.cn>
>>
>> Introduce exfat_chain_advance() to walk a exfat_chain structure by a
>> given step, updating both ->dir and ->size fields atomically. This
>> helper handles both ALLOC_NO_FAT_CHAIN and ALLOC_FAT_CHAIN modes with
>> proper boundary checking.
>>
>> Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
>> Tested-by: syzbot@syzkaller.appspotmail.com
>>
>> ---
>> fs/exfat/exfat_fs.h | 17 +++++++++++++++++
>>   1 file changed, 17 insertions(+)
>>
>> diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
>> index 530459ab9acc..1035d20ba563 100644
>> --- a/fs/exfat/exfat_fs.h
>> +++ b/fs/exfat/exfat_fs.h
>> @@ -552,6 +552,23 @@ int exfat_read_volume_label(struct super_block *sb,
>> int exfat_write_volume_label(struct super_block *sb,
>>                               struct exfat_uni_name *label);
>>
>> +static inline int exfat_chain_advance(struct super_block *sb,
>> +               struct exfat_chain *chain, unsigned int step)
>> +{
>> +       if (chain->size >= step)
>> +               chain->size -= step;
> 
> It would be better to not change *chain if return an error.

Okay,

v3:

static inline int exfat_chain_advance(struct super_block *sb,
                 struct exfat_chain *chain, unsigned int step)
{
         if (chain->size < step)
                 return -EIO;

         chain->size -= step;

         if (exfat_fat_walk(sb, &chain->dir, step, chain->flags))
                 return -EIO;

         if (chain->size == 0 && chain->flags == ALLOC_NO_FAT_CHAIN)
                 chain->dir = EXFAT_EOF_CLUSTER;

         return 0;
}


Thanks,
> 
>> +       else
>> +               return -EIO;
>> +
>> +       if (exfat_fat_walk(sb, &chain->dir, step, chain->flags))
>> +               return -EIO;
>> +
>> +       if (chain->size == 0 && chain->flags == ALLOC_NO_FAT_CHAIN)
>> +               chain->dir = EXFAT_EOF_CLUSTER;
>> +
>> +       return 0;
>> +}
>> +
>>   /* inode.c */
>>   extern const struct inode_operations exfat_file_inode_operations;
>>   void exfat_sync_inode(struct inode *inode);
>> --
>> 2.43.0
> 
>