linux-kernel - Re: [PATCH v12 2/6] ring-buffer: Introducing ring-buffer mapping functions

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Message-ID: <Za_74T-IJWAa6fny@google.com>
Date: Tue, 23 Jan 2024 17:48:17 +0000
From: Vincent Donnefort <vdonnefort@...gle.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: mhiramat@...nel.org, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com,
	kernel-team@...roid.com
Subject: Re: [PATCH v12 2/6] ring-buffer: Introducing ring-buffer mapping
 functions

On Tue, Jan 23, 2024 at 10:51:49AM -0500, Steven Rostedt wrote:
> On Tue, 23 Jan 2024 11:07:53 +0000
> Vincent Donnefort <vdonnefort@...gle.com> wrote:
> 
> > index 000000000000..5468afc94be7
> > --- /dev/null
> > +++ b/include/uapi/linux/trace_mmap.h
> > @@ -0,0 +1,44 @@
> > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > +#ifndef _TRACE_MMAP_H_
> > +#define _TRACE_MMAP_H_
> > +
> > +#include <linux/types.h>
> > +
> > +/**
> > + * struct trace_buffer_meta - Ring-buffer Meta-page description
> > + * @meta_page_size:	Size of this meta-page.
> > + * @meta_struct_len:	Size of this structure.
> > + * @subbuf_size:	Size of each subbuf, including the header.
> > + * @nr_subbufs:		Number of subbfs in the ring-buffer.
> > + * @reader.lost_events:	Number of events lost at the time of the reader swap.
> > + * @reader.id:		subbuf ID of the current reader. From 0 to @nr_subbufs - 1
> > + * @reader.read:	Number of bytes read on the reader subbuf.
> > + * @entries:		Number of entries in the ring-buffer.
> > + * @overrun:		Number of entries lost in the ring-buffer.
> > + * @read:		Number of entries that have been read.
> 
> 
> > + * @subbufs_touched:	Number of subbufs that have been filled.
> > + * @subbufs_lost:	Number of subbufs lost to overrun.
> > + * @subbufs_read:	Number of subbufs that have been read.
> 
> Do we actually need the above 3 fields?
> 
> What's the use case for them? I don't want to expose internals in the API
> unless they are needed.

subbufs_read is gone, I just forgot to remove it here :-\.

The two other ones are used for tracing with the hypervisor. That's why I
preemptively added them. 

I can remove them and add just append this struct later ... or just overload
this struct with another one, only shared between the kernel and the hypervisor?

> 
> -- Steve