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 [off-list ref] wrote:

quoted

--- /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.

quoted

+ * @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.

quoted

+ * @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

quoted

+ */
+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_ */