Re: [PATCH v5 7/7] string: Implement strstarts() with strprefix()

[Alejandro Colomar]

Hi Andy,

> Date: 2026-11-13 16:44:08+0200
> From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>
>
> On Fri, Nov 13, 2026 at 02:11:17PM +0100, Alejandro Colomar wrote:
> > The compiler should be able to optimize out the unused pointer
> > arithmetic done at the end, so performance-wise this shouldn't change
> > anything.
> 
> If strprefix() is not inline how would it be done? Or I missed the point?

But strprefix() is inline.

> > This change de-duplicates the almost-identical implementations,
> > and better shows the relationship between the two functions.
> 
> ...
> 
> >  static inline bool strstarts(const char *str, const char *prefix)
> >  {
> > -	return strncmp(str, prefix, strlen(prefix)) == 0;
> > +	return strprefix(str, prefix);
> >  }
> 
> There is no sense to keep strstarts() at this point.

I agree.  Actually, it seems my guess that strprefix() would be
optimized out was wrong, because the kernel builds with
-fno-delete-null-pointer-checks and other flags that prevent this
optimization.

> Can it be simply redefinition?

I was thinking that we could just do a simple search and replace
s/strstarts/strends/, prepending !! in some cases if needed.

By 'redefinition', do you mean making strstarts() return a pointer
instead of a bool?  A problem with strstarts() is again the function
name: it doesn't seem to naturally fit with a function that returns a
pointer to the position.  It also doesn't clarify whether it searches
for a string, or for a list of characters (like for example strspn(3)).

I prefer replacing strstarts()/strends() with strprefix()/strsuffix().

But if you prefer changing strstarts() to return a pointer, I'm also
okay-ish with it.  It's not a perfect name, but I can live with it.

> However, after looking at the uses in the kernel, I prefer
> to see the strprefix() be not implemented at all, just optimization against
> strstarts()/strends() if required can be performed.

I don't understand this last sentence.


Cheers,
Alex

> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
> 

-- 
<https://www.alejandro-colomar.es>

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