Re: [RFC 1/9] lib/string: Add function to trim duplicate WS

[Tony Asleson <tasleson@redhat.com>]

On 1/2/20 4:52 PM, Tony Asleson wrote:
> On 12/23/19 5:28 PM, Matthew Wilcox wrote:
>> On Mon, Dec 23, 2019 at 04:55:50PM -0600, Tony Asleson wrote:
>>> +/**
>>> + * Removes leading and trailing whitespace and removes duplicate
>>> + * adjacent whitespace in a string, modifies string in place.
>>> + * @s The %NUL-terminated string to have spaces removed
>>> + * Returns the new length
>>> + */
>>
>> This isn't good kernel-doc.  See Documentation/doc-guide/kernel-doc.rst
>> Compile with W=1 to get the format checked.
> 
> Indeed, I'll correct it.
> 
>>> +size_t strim_dupe(char *s)
>>> +{
>>> +	size_t ret = 0;
>>> +	char *w = s;
>>> +	char *p;
>>> +
>>> +	/*
>>> +	 * This will remove all leading and duplicate adjacent, but leave
>>> +	 * 1 space at the end if one or more are present.
>>> +	 */
>>> +	for (p = s; *p != '\0'; ++p) {
>>> +		if (!isspace(*p) || (p != s && !isspace(*(p - 1)))) {
>>> +			*w = *p;
>>> +			++w;
>>> +			ret += 1;
>>> +		}
>>> +	}
>>
>> I'd be tempted to do ...
>>
>> 	size_t ret = 0;
>> 	char *w = s;
>> 	bool last_space = false;
>>
>> 	do {
>> 		bool this_space = isspace(*s);
>>
>> 		if (!this_space || !last_space) {
>> 			*w++ = *s;
>> 			ret++;
>> 		}
>> 		s++;
>> 		last_space = this_space;
>> 	} while (s[-1] != '\0');
> 
> That leaves a starting and trailing WS, how about something like this?
> 
> size_t strim_dupe(char *s)
> {
> 	size_t ret = 0;
> 	char *w = s;
> 	bool last_space = false;
> 
> 	do {
> 		bool this_space = isspace(*s);
> 		if (!this_space || (!last_space && ret)) {Mollie Fitzgerald
> 			*w++ = *s;
> 			ret++;
> 		}
> 		s++;
> 		last_space = this_space;
> 	} while (s[-1] != '\0');
> 
> 	if (ret > 1 && isspace(w[-2])) {
> 		w[-2] = '\0';
> 		ret--;
> 	}
> 
> 	ret--;
> 	return ret;
> }

This function was added so I could strip out extra spaces in the vpd
0x83 string representation, to shorten them before they get added to the
structured syslog message.  I'm starting to think this is a bad idea as
anyone that might want to write some code to use the kernel sysfs entry
for a device and search for it in the syslog would have to perturb the
id string the same way.

I think this change should just be removed from the patch series and
leave the IDs as they are.

If we really wanted a shorter ID, a better approach would be use a hash
of the ID string, but that introduces another level of complexity that
isn't helpful to end users.

-Tony