linux-kernel - Re: [PATCH v2 1/2] ring-buffer: Introducing ring-buffer mapping functions

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Message-ID: <20230329080758.0e730796@rorschach.local.home>
Date:   Wed, 29 Mar 2023 08:07:58 -0400
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 v2 1/2] ring-buffer: Introducing ring-buffer mapping
 functions

On Wed, 29 Mar 2023 07:03:53 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> struct ring_buffer_meta_page_header {
> #if __BITS_PER_LONG == 64
> 	__u64	entries;
> 	__u64	overrun;
> #else
> 	__u32	entries;
> 	__u32	overrun;
> #endif
> 	__u32	pages_touched;
> 	__u32	meta_page_size;
> 	__u32	reader_page;	/* page ID for the reader page */
> 	__u32	nr_data_pages;	/* doesn't take into account the reader_page */
> };
> 
> BTW, shouldn't the nr_data_pages take into account the reader page? As it
> is part of the array we traverse isn't it?

Ah, I guess nr_data_pages is the length of the index mapping, not the
array of pages mapped?

-- Steve