linux-kernel - Re: [PATCH v2 1/7] string.h: add str_has_suffix() helper for test string ends with specify string

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Date: Tue, 23 Jan 2024 10:36:36 +0800
From: "yebin (H)" <yebin10@...wei.com>
To: Steven Rostedt <rostedt@...dmis.org>
CC: <mhiramat@...nel.org>, <mathieu.desnoyers@...icios.com>,
	<linux-trace-kernel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/7] string.h: add str_has_suffix() helper for test
 string ends with specify string



On 2024/1/23 0:07, Steven Rostedt wrote:
> On Mon, 22 Jan 2024 15:40:09 +0800
> Ye Bin <yebin10@...wei.com> wrote:
>
>> str_has_suffix() is test string if ends with specify string.
>>
>> Signed-off-by: Ye Bin <yebin10@...wei.com>
>> ---
>>   include/linux/string.h | 20 ++++++++++++++++++++
>>   1 file changed, 20 insertions(+)
>>
>> diff --git a/include/linux/string.h b/include/linux/string.h
>> index 433c207a01da..e47e9597af27 100644
>> --- a/include/linux/string.h
>> +++ b/include/linux/string.h
>> @@ -405,4 +405,24 @@ static __always_inline size_t str_has_prefix(const char *str, const char *prefix
>>   	return strncmp(str, prefix, len) == 0 ? len : 0;
>>   }
>>   
>> +/**
>> + * str_has_suffix - Test if a string has a given suffix
>> + * @str: The string to test
>> + * @suffix: The string to see if @str ends with
>> + *
>> + * Returns:
>> + * * strlen(@suffix) if @str ends with @suffix
>> + * * 0 if @str does not end with @suffix
>> + */
>> +static __always_inline size_t str_has_suffix(const char *str, const char *suffix)
>> +{
>> +	size_t len = strlen(suffix);
>> +	size_t str_len = strlen(str);
>> +
>> +	if (len > str_len)
>> +		return 0;
>> +
>> +	return strncmp(str + str_len - len, suffix, len) == 0 ? len : 0;
>> +}
> I understand why you are returning the length of the suffix, as it matches
> str_has_prefix(). But as the user of this will likely need the length of
> the "str" too, we should either return the length of the string, or the
> index of where the suffix was found.
>
> /**
>   [..]
>   @index: The index into @str of where @suffix is if found (NULL to ignore)
>   [..]
> */
> static __always_inline size_t str_has_suffix(const char *str, const char *suffix, size_t *index)
> {
> 	size_t len = strlen(suffix);
> 	size_t str_len = strlen(str);
>
> 	if (len > str_len)
> 		return 0;
>
> 	if (index)
> 		*index = str_len - len;
>
> 	return strncmp(str + str_len - len, suffix, len) == 0 ? len : 0;
> }
>
> -- Steve
Thank you for your advice.
Return the index of where the suffix was found is useful. I'll modify it 
according to your suggestion.

-- Ye Bin
>> +
>>   #endif /* _LINUX_STRING_H_ */
> .
>