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

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Date:   Wed, 29 Mar 2023 08:51:06 -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 */
> };

Oh, I guess we should also expose the amount read on the reader page,
that gets updated on the ioctl. That is, if the first time we read the
reader page and the page is not full and unmap the pages, and then new
events were added to the reader page, we should not re-read the events
that were read previously.

That is, expose cpu_buffer->reader_page->read

-- Steve