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

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

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:
> chenxiaosong.chenxiaosong@linux.dev wrote:
> 
>> +static __always_inline int cmp_smb2_status(const void *_a, const void *_b)
>> +{
>> +	const struct status_to_posix_error *a = _a, *b = _b;
>> +
>> +	if (a->smb2_status < b->smb2_status)
>> +		return -1;
>> +	if (a->smb2_status > b->smb2_status)
>> +		return 1;
>> +	return 0;
>> +}
> 
> 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