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 <[email protected]>
>
> 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
>
