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

Tony Asleson
2020-01-03T14:30:22Z

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