Re: [PATCH v6 4/5] smb/client: use bsearch() to find target in smb2_error_map_table

[ChenXiaoSong <chenxiaosong.chenxiaosong@linux.dev>]

Hi David,

Your second suggestion looks good. Should we change it to the following 
code? If you are okay with these changes, I can send the next version.

```
__inline_bsearch((const void *)(unsigned long)smb2_status, ...);

static __always_inline int cmp_smb2_status(const void *_key, const void 
*_pivot)
{
         __le32 key = (unsigned long)_key;
         const struct status_to_posix_error *pivot = _pivot;

         if (key < pivot->smb2_status)
                 return -1;
         if (key > pivot->smb2_status)
                 return 1;
         return 0;
}
```

Thanks,
ChenXiaoSong <chenxiaosong@kylinos.cn>

On 12/26/25 11:28 PM, ChenXiaoSong wrote:
> Hi David,
> 
> We cannot use "return b->smb2_status - a->smb2_status".
> 
> For example:
> 
>      a_status = 0xC0000005
>      b_status = 0x00000001
> 
> The subtraction is evaluated in an unsigned type:
> 
>      a_status - b_status = 0xC0000004 > 0
> 
> But the comparison function returns int, so the value is converted:
> 
>      (int)(a_status - b_status) < 0
> 
> Thanks,
> ChenXiaoSong.
> 
> On 12/26/25 8:06 PM, David Howells wrote:
>>
>> Actually...  It's probably sufficient to do:
>>
>>     static __always_inline
>>     int cmp_smb2_status(const void *_a, const void *_b)
>>     {
>>         const struct status_to_posix_error *a = _a, *b = _b;
>>
>>         return b->smb2_status - a->smb2_status;
>>     }
>>
>> as __inline_bsearch() only cares about the zeroness or sign of the return
>> value.  (Note the arguments to the subtraction might need to be flipped).
>>
>> It might even better just to cast the smb status you're looking for to 
>> the key
>> parameter:
>>
>>     __inline_bsearch((const void *)(long)status, ...);
>>
>> and then do this in the comparison function:
>>
>>     static __always_inline
>>     int cmp_smb2_status(const void *key, const void *_b)
>>     {
>>         const struct status_to_posix_error *b = _b;
>>         int status = (long)key;
>>
>>         return b->smb2_status - status;
>>     }
>>
>> as __inline_bsearch() doesn't attempt to dereference key.
>>
>> David
>