Re: [PATCH v1] ring-buffer: Rename ring_buffer_size() to ring_buffer_capacity()

[Vincent Donnefort <vdonnefort@google.com>]

On Mon, Sep 07, 2026 at 10:42:38AM +0100, Vincent Donnefort wrote:
> Since commit 8a5f63637890 ("ring-buffer: Fix subbuf resize race with ring
> buffer readers"), "capacity" refers to the memory available for events
> (excluding subbuffer headers) while "size" refers to the raw allocation.
> ring_buffer_size() actually calculates this event capacity. Rename it to
> ring_buffer_capacity() to align with this convention.
> 
> Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
> 
> diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
> index afc7daa6ee7d..9e23ab66176b 100644
> --- a/include/linux/ring_buffer.h
> +++ b/include/linux/ring_buffer.h
> @@ -165,7 +165,7 @@ void ring_buffer_iter_reset(struct ring_buffer_iter *iter);
>  int ring_buffer_iter_empty(struct ring_buffer_iter *iter);
>  bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter);
>  
> -unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu);
> +unsigned long ring_buffer_capacity(struct trace_buffer *buffer, int cpu);
>  unsigned long ring_buffer_max_event_size(struct trace_buffer *buffer);
>  
>  void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu);
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 9c03a555a6ba..2940ff763354 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -6547,18 +6547,23 @@ void ring_buffer_iter_advance(struct ring_buffer_iter *iter)
>  EXPORT_SYMBOL_GPL(ring_buffer_iter_advance);
>  
>  /**
> - * ring_buffer_size - return the size of the ring buffer (in bytes)
> + * ring_buffer_capacity - return the capacity of the ring buffer (in bytes)
>   * @buffer: The ring buffer.
> - * @cpu: The CPU to get ring buffer size from.
> + * @cpu: The CPU to get ring buffer capacity from.
> + *
> + * Capacity is the total memory available for recording event data in the
> + * ring buffer. It excludes subbufer headers.

Of course, I manage to do a typo... "subbuffer" 

-- 
Vincent

> + *
> + * Returns the capacity in bytes, or 0 if the CPU is not set in the buffer mask.
>   */
> -unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu)
> +unsigned long ring_buffer_capacity(struct trace_buffer *buffer, int cpu)
>  {
>  	if (!cpumask_test_cpu(cpu, buffer->cpumask))
>  		return 0;
>  
>  	return rb_subbuf_capacity(buffer) * buffer->buffers[cpu]->nr_pages;
>  }
> -EXPORT_SYMBOL_GPL(ring_buffer_size);
> +EXPORT_SYMBOL_GPL(ring_buffer_capacity);
>  
>  /**
>   * ring_buffer_max_event_size - return the max data size of an event
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 8658cad53cb5..f0251788ec75 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -4712,9 +4712,9 @@ void trace_set_buffer_entries(struct array_buffer *buf, unsigned long val)
>  static void update_buffer_entries(struct array_buffer *buf, int cpu)
>  {
>  	if (cpu == RING_BUFFER_ALL_CPUS) {
> -		trace_set_buffer_entries(buf, ring_buffer_size(buf->buffer, 0));
> +		trace_set_buffer_entries(buf, ring_buffer_capacity(buf->buffer, 0));
>  	} else {
> -		per_cpu_ptr(buf->data, cpu)->entries = ring_buffer_size(buf->buffer, cpu);
> +		per_cpu_ptr(buf->data, cpu)->entries = ring_buffer_capacity(buf->buffer, cpu);
>  	}
>  }
>  
> @@ -8476,7 +8476,7 @@ int allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int
>  
>  	/* Allocate the first page for all buffers */
>  	trace_set_buffer_entries(&tr->array_buffer,
> -				 ring_buffer_size(tr->array_buffer.buffer, 0));
> +				 ring_buffer_capacity(tr->array_buffer.buffer, 0));
>  
>  	return 0;
>  }
> 
> base-commit: df2908090cda368b01ff43709f51890076c56157
> -- 
> 2.55.0.979.g7e5102b832-goog
>