linux-kernel - Re: [PATCH v13 2/6] ring-buffer: Introducing ring-buffer mapping functions

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Date: Mon, 5 Feb 2024 09:43:57 +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 v13 2/6] ring-buffer: Introducing ring-buffer mapping
 functions

On Sat, Feb 03, 2024 at 07:33:51PM -0500, Steven Rostedt wrote:
> On Mon, 29 Jan 2024 14:27:58 +0000
> Vincent Donnefort <vdonnefort@...gle.com> wrote:
> 
> > --- /dev/null
> > +++ b/include/uapi/linux/trace_mmap.h
> > @@ -0,0 +1,43 @@
> > +/* 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.
> 
> That is "the header"?

I mean the header of the "bpage". But that is confusing. I'll either remove that
mention or just say it is aligned with the order of a system page size.

> 
> > + * @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.
> 
> Note, flags needs a comment.
> 
> > + * @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.
> 
> So does the two Reserved words, otherwise I'm going to start getting
> error reports about sparse warnings that check kerneldoc comments
> against their content. Every field needs to be represented in the
> kerneldoc comment.

Ack, wasn't sure it was needed.

> 
> -- Steve
> 
> 
> > + */
> > +struct trace_buffer_meta {
> > +	__u32		meta_page_size;
> > +	__u32		meta_struct_len;
> > +
> > +	__u32		subbuf_size;
> > +	__u32		nr_subbufs;
> > +
> > +	struct {
> > +		__u64	lost_events;
> > +		__u32	id;
> > +		__u32	read;
> > +	} reader;
> > +
> > +	__u64	flags;
> > +
> > +	__u64	entries;
> > +	__u64	overrun;
> > +	__u64	read;
> > +
> > +	__u64	Reserved1;
> > +	__u64	Reserved2;
> > +};
> > +
> > +#endif /* _TRACE_MMAP_H_ */