[PATCH] ring-buffer: Use a macro for static buffer bits

[PATCH] ring-buffer: Use a macro for static buffer bits

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

Instead of hard coding 30 for the number of bits used for the static
buffer ids in two places, create a macro. This way if it changes in the
future, it will change in all the locations that use it.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 220b8405adfc..b88c75b52e8f 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -335,6 +335,9 @@ static __always_inline unsigned int rb_read_page_capacity(struct buffer_data_rea
 	return (PAGE_SIZE << rpage->order) - BUF_PAGE_HDR_SIZE;
 }
 
+/* The number of bits for static buffer ids */
+#define RB_STATIC_BITS	30
+
 /*
  * Note, the buffer_page list must be first. The buffer pages
  * are allocated in cache lines, which means that each buffer
@@ -350,7 +353,7 @@ struct buffer_page {
 	local_t		 entries;	/* entries on this page */
 	unsigned long	 real_end;	/* real end of data */
 	unsigned	 order;		/* order of the page */
-	u32		 id:30;		/* ID for external mapping */
+	u32		 id:RB_STATIC_BITS; /* ID for external mapping */
 	u32		 range:1;	/* Mapped via a range */
 	struct buffer_data_page *page;	/* Actual data page */
 };
@@ -663,7 +666,7 @@ static unsigned long rb_static_max_pages(void)
 	 * Static ring buffers are using bpage::id and must account for the
 	 * reader page.
 	 */
-	return (1UL << 30) - 1;
+	return (1UL << RB_STATIC_BITS) - 1;
 }
 
 struct ring_buffer_iter {
-- 
2.53.0

Re: [PATCH] ring-buffer: Use a macro for static buffer bits

[Vincent Donnefort]

On Fri, Sep 04, 2026 at 03:16:41PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@goodmis.org>
> 
> Instead of hard coding 30 for the number of bits used for the static
> buffer ids in two places, create a macro. This way if it changes in the
> future, it will change in all the locations that use it.
> 
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
>  kernel/trace/ring_buffer.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 220b8405adfc..b88c75b52e8f 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -335,6 +335,9 @@ static __always_inline unsigned int rb_read_page_capacity(struct buffer_data_rea
>  	return (PAGE_SIZE << rpage->order) - BUF_PAGE_HDR_SIZE;
>  }
>  
> +/* The number of bits for static buffer ids */
> +#define RB_STATIC_BITS	30
> +
>  /*
>   * Note, the buffer_page list must be first. The buffer pages
>   * are allocated in cache lines, which means that each buffer
> @@ -350,7 +353,7 @@ struct buffer_page {
>  	local_t		 entries;	/* entries on this page */
>  	unsigned long	 real_end;	/* real end of data */
>  	unsigned	 order;		/* order of the page */
> -	u32		 id:30;		/* ID for external mapping */
> +	u32		 id:RB_STATIC_BITS; /* ID for external mapping */
>  	u32		 range:1;	/* Mapped via a range */
>  	struct buffer_data_page *page;	/* Actual data page */
>  };
> @@ -663,7 +666,7 @@ static unsigned long rb_static_max_pages(void)
>  	 * Static ring buffers are using bpage::id and must account for the
>  	 * reader page.
>  	 */
> -	return (1UL << 30) - 1;
> +	return (1UL << RB_STATIC_BITS) - 1;
>  }
>  
>  struct ring_buffer_iter {
> -- 
> 2.53.0
>

Reviewed-by: Vincent Donnefort <vdonnefort@google.com>

-- 
Vincent