Re: [PATCH 1/1] container_of: Document container_of_const() is preferred

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Jun 18, 2024 at 02:56:17PM +0100, Matthew Wilcox wrote:
> On Tue, Jun 18, 2024 at 02:54:53PM +0200, Greg Kroah-Hartman wrote:
> > > I didn't have any issues (apart from me misspelling function names ;)) with
> > > GCC 12, neither in using container_of_const() in a static inline function
> > > nor in using a static inline function as a _Generic() expression.
> > 
> > Really?  And how do you handle the pointer being either const or not,
> > and propagating that back out as the return type?  I'd like to see your
> > inline function please.
> 
> Here's how I did it for page_folio():
> 
> #define page_folio(p)           (_Generic((p),                          \
>         const struct page *:    (const struct folio *)_compound_head(p), \
>         struct page *:          (struct folio *)_compound_head(p)))
> 
> Is there something differently magic about container_of() that prevents
> this trick from working?

That's a #define, not an inline function, which is what I thought we
were talking about.

thanks,

greg k-h