linux-kernel - Re: [PATCH v9 1/2] ring-buffer: Introducing ring-buffer mapping functions

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Date: Thu, 4 Jan 2024 13:28:50 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Vincent Donnefort <vdonnefort@...gle.com>
Cc: mhiramat@...nel.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v9 1/2] ring-buffer: Introducing ring-buffer mapping
 functions

On Thu, 21 Dec 2023 12:58:13 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Thu, 21 Dec 2023 17:35:22 +0000
> Vincent Donnefort <vdonnefort@...gle.com> wrote:
> 
> > @@ -5999,6 +6078,307 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
> >  }
> >  EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set);
> >    
> 
> The kernel developers have agreed to allow loop variables to be declared in
> loops. This will simplify these macros:
> 
> 
> 
> > +#define subbuf_page(off, start) \
> > +	virt_to_page((void *)(start + (off << PAGE_SHIFT)))
> > +
> > +#define foreach_subbuf_page(off, sub_order, start, page)	\
> > +	for (off = 0, page = subbuf_page(0, start);		\
> > +	     off < (1 << sub_order);				\
> > +	     off++, page = subbuf_page(off, start))  
> 
> #define foreach_subbuf_page(sub_order, start, page)		\
> 	for (int __off = 0, page = subbuf_page(0, (start));	\
> 	     __off < (1 << (sub_order));			\
> 	     __off++, page = subbuf_page(__off, (start)))

So it seems that you can't declare "int __off" with page there, but we
could have:

#define foreach_subbuf_page(sub_order, start, page)		\
	page = subbuf_page(0, (start));				\
	for (int __off = 0; __off < (1 << (sub_order));		\
	     __off++, page = subbuf_page(__off, (start)))


And that would work.

-- Steve