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

[Alejandro Colomar <alx@kernel.org>]

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Hi Andy,

> Date: 2026-11-13 17:07:35+0200
> From: Andy Shevchenko <andriy.shevchenko@intel.com>
>
> On Fri, Nov 13, 2026 at 03:59:46PM +0100, Alejandro Colomar wrote:
> > > On Fri, Nov 13, 2026 at 02:11:17PM +0100, Alejandro Colomar wrote:
> 
> ...
> 
> > > >  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)).
> 
> We have str_has_*() for that?

I don't fully understand.  str_has_prefix() --which is the only
str_has_*() function, BTW-- is meant to be the same as strprefix(),
except for using an offset instead of a pointer.

-  strstarts():
	It could be improved by returning a boolean-like pointer,
	instead of a bool, but:

	-  We may need to fix some callers, since some of them might
	   need an explicit conversion with !!.  It'd be risky to change
	   the implementation without first verifying that.

	   To avoid that risk, I prefer adding a new API, and
	   deprecating strstarts() for new code.  Over time, I could
	   slowly migrate users from strstarts() to strprefix().

	-  The name isn't ideal, since "starts" doesn't specify whether
	   it looks for a string that starts with a given prefix, or if
	   it looks for a string that starts with any of the given
	   characters.

	   That is, by the name, I wouldn't be able to know whether
	   strstarts implements

		bool strstarts(const char *s, const char *xxx)
		{
			return strspn(s, xxx);
		}
	   or
		bool strstarts(const char *s, const char *xxx)
		{
			return strprefix(s, xxx);
		}

-  strends():
	Same as with strstarts() but from the end.

-  str_has_prefix():
	It was an attempt at strprefix(), but with a problematic
	approach.  It's frozen because of trace code.

-  strprefix()/strsuffix():
	I'd add them to slowly replace strstarts()/strends().

> 
> > 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.
> 
> It's basically repeats the idea of having only one pair out of two.

Ok.

> With this series will be
> 
> str_has_previx()
> strstarts()
> strends()
> strprefix()
> // potentially strsuffix()

Yes.  I'd like to replace strstarts()/strends() with
strprefix()/strsuffix(), but prefer to do that slowly, to avoid
introducing bugs due to missing explicit conversions to bool.

Should I add notes that the strstarts()/strends() APIs are deprecated?

> To me seems too many for the similar task. I understand that trace user is
> special one, but does it use strstarts()/strends()?

I didn't find any uses:

	$ git ls-files | grep kernel/trace/ | xargs grep strstarts
	$ git ls-files | grep kernel/trace/ | xargs grep strends

> Despite on naming I think we just good to have only str_has*() and one of
> strprefix()/strsuffix(), strstarts()/strends().

In the long term, I agree.  But I think the transition should be
careful.  What do you think?


Cheers,
Alex

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

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

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