Re: [PATCH 5/9] of: property: implement the .property_get_names() fwnode operation

[Alejandro Colomar <alx+linux-hardening@kernel.org>]

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> Date: 2026-11-10 12:35:22+0100
> From: Alejandro Colomar <alx+linux-hardening@kernel.org>
>
> > Date: 2026-11-10 12:10:57+0100
> > From: Alejandro Colomar <alx+linux-hardening@kernel.org>
> >
> > Hi Bart,
> > 
> > > Date: 2026-11-10 10:00:42+0100
> > > From: Bartosz Golaszewski <brgl@kernel.org>
> > >
> > [...]
> > > > > > > +		names[i] = kstrdup(prop->name, GFP_KERNEL);
> > > > > > 
> > > > > > Can property be statically defined somewhere? We might want to also optimize
> > > > > > these duplications with const variant (here or elsewhere, for fwnode generic
> > > > > > path, I believe).
> > > > > 
> > > > > Please rephrase because I'm not quite following what you're saying.
> > > > 
> > > > Can prop->name come from something that is declared as
> > > > 
> > > > static const ... foo = {
> > > > 	... .name = "bar";
> > > > };
> > > >
> > > 
> > > You can't know it for every instance of struct fwnode_handle, so the
> > > answer is: no.
> > > 
> > > PS: is there a way of using match_string() with non-const data?
> > 
> > Given the definition here:
> > 
> > 	$ grepc match_string .
> > 	./include/linux/string.h:int match_string(const char * const *array, size_t n, const char *string);
> > 	./lib/string_helpers.c:int match_string(const char * const *array, size_t n, const char *string)
> > 	{
> > 		int index;
> > 		const char *item;
> > 
> > 		for (index = 0; index < n; index++) {
> > 			item = array[index];
> > 			if (!item)
> > 				break;
> > 			if (!strcmp(item, string))
> > 				return index;
> > 		}
> > 
> > 		return -EINVAL;
> > 	}
> > 
> > You should be able to call it with a cast.  It's dangerous, but
> > technically it works.  I'm not encouraging it, though.  :)
> > 
> > 	char **strings;
> > 
> > 	...
> > 
> > 	i = match_string((const char *const *) strings, n, "foo");
> > 
> > This is a historic problem in C, which was solved in C++.
> 
> BTW, self-correction:  it is solved for char *const *, but char** is not
> convertible to const char *const *, neither in C++ nor in future C.

Self-correction of the self-correction: char ** will also be convertible
to const char *const *.  I was confused during a short moment, it seems.

	alx@devuan:~/tmp$ cat const.c 
	#include <stddef.h>

	int
	main(void)
	{
		const char *const *ccp = NULL;
		char **p;

		ccp = p;
	}
	alx@devuan:~/tmp$ cat const.c | gcc -x c++ -
	alx@devuan:~/tmp$ 


Cheers,
Alex

> 
> 
> Cheers,
> Alex
> 
> >  I have
> > a proposal paper for the C Committee for solving it as in C++:
> > <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3987.htm>
> > 
> > This paper will be discussed (and probably voted in) in the next meeting
> > of the committee (which happens next week), so there's a chance that
> > this will be solved for C2y, and thus the cast will no longer be
> > necessary.
> > 
> > The history of why this is not allowed in C but is in C++ is, as far as
> > I've been told, the following:
> > 
> > Back before C and C++ were standardized, C++ invented const, with rules
> > slightly more allowing than what they are now.  This was going to be
> > standardized first in C89.  But very close to the release of C89, they
> > realized about the danger of converting a const char** to a char**
> > implicitly.  They were so close to the release, that they opted for the
> > safest approach: disallow any non-trivial conversions.
> > 
> > Later, while standardizing C++98, they realized we could allow a few
> > more conversions safely, and so they did.
> > 
> > C could have taken advantage of that, and pick C++ rules in C99 or C11,
> > but for some reason, nobody proposed that.  I'm proposing it now.  :)
> > 
> > We've already discussed this proposal informally within the committee
> > for some a year and a half, and there seems to be consensus that we want
> > it.  We're only being careful about the specific language.  But I think
> > I finally got it, and it will go in next week.
> > 
> > 
> > Have a lovely day!
> > Alex
> > 
> > > 
> > > Bart
> > > 
> > 
> > -- 
> > <https://www.alejandro-colomar.es>
> 
> 
> 
> -- 
> <https://www.alejandro-colomar.es>



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

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