Re: [PATCH v5 07/14] gtrace: Add function to copy into perf AUX buffer

[Zane Leung]

On 8/10/2026 11:22 PM, Mayuresh Chitale wrote:

> From: Anup Patel <anup.patel@xxxxxxxxxxxxxxxx>
>
> The RISC-V trace ramsink will need a mechanism to copy trace data
> into the perf AUX buffer. Add gtrace_path_copyto_auxbuf() function
> and corresponding trace driver callback copyto_auxbuf() for this
> purpose.
>
> Co-developed-by: Mayuresh Chitale <mayuresh.chitale@xxxxxxxxxxxxxxxx>
> Signed-off-by: Mayuresh Chitale <mayuresh.chitale@xxxxxxxxxxxxxxxx>
> Signed-off-by: Anup Patel <anup.patel@xxxxxxxxxxxxxxxx>
> ---
>  drivers/hwtracing/gtrace/gtrace-core.c | 22 ++++++++++++++++++++++
>  include/linux/gtrace.h                 | 24 ++++++++++++++++++++++++
>  2 files changed, 46 insertions(+)
>
> diff --git a/drivers/hwtracing/gtrace/gtrace-core.c b/drivers/hwtracing/gtrace/gtrace-core.c
> index 6ff1b3087947..53a3679ba69f 100644
> --- a/drivers/hwtracing/gtrace/gtrace-core.c
> +++ b/drivers/hwtracing/gtrace/gtrace-core.c
> @@ -626,6 +626,28 @@ int gtrace_path_stop(struct gtrace_path *path)
>  }
>  EXPORT_SYMBOL_GPL(gtrace_path_stop);
>  
> +int gtrace_path_copyto_auxbuf(struct gtrace_path *path,
> +			      struct gtrace_perf_auxbuf *buf,
> +			      size_t *bytes_copied, u64 *format)
> +{
> +	const struct gtrace_driver *gtdrv;
> +	struct gtrace_component *comp;
> +	struct gtrace_path_node *node;
> +
> +	list_for_each_entry(node, &path->comp_list, head) {
> +		comp = node->comp;
> +		gtdrv = to_gtrace_driver(comp->dev.driver);
> +		if (!gtdrv->copyto_auxbuf)
> +			continue;
> +
> +		*bytes_copied = gtdrv->copyto_auxbuf(comp, buf, format);
> +		return 0;
> +	}
> +
> +	return -EOPNOTSUPP;
> +}
> +EXPORT_SYMBOL_GPL(gtrace_path_copyto_auxbuf);

Is it really necessary to introduce `gtrace_path_copyto_auxbuf`? The buffer copy logic should be
exclusive to the sink component.
A cleaner approach would be to delegate this directly to the sink instance:
```
struct gtrace_component *sink = gtrace_path_sink(path);
size = sink->copyto_auxbuf(sink, &event_data->buf, &format);
```

> +
>  struct gtrace_path *gtrace_create_path(struct gtrace_component *source,
>  				       struct gtrace_component *sink,
>  				       enum gtrace_component_mode mode)
> diff --git a/include/linux/gtrace.h b/include/linux/gtrace.h
> index 78e2ead3db8e..bc82814e2738 100644
> --- a/include/linux/gtrace.h
> +++ b/include/linux/gtrace.h
> @@ -257,9 +257,30 @@ void gtrace_destroy_path(struct gtrace_path *path);
>  int gtrace_path_start(struct gtrace_path *path);
>  int gtrace_path_stop(struct gtrace_path *path);
>  
> +/**
> + * struct gtrace_perf_auxbuf - Representation of the perf AUX buffer.
> + * @length:   Size of the AUX buffer.
> + * @nr_pages: Number of pages of the AUX buffer.
> + * @base:     Start address of AUX buffer.
> + * @pos:      Position in the AUX buffer to commit traced data.
> + */
> +struct gtrace_perf_auxbuf {
> +	size_t length;
> +	int nr_pages;
> +	void *base;
> +	long pos;
> +};
> +
> +int gtrace_path_copyto_auxbuf(struct gtrace_path *path,
> +			      struct gtrace_perf_auxbuf *buf,
> +			      size_t *bytes_copied, u64 *format);
> +
>  /**
>   * struct gtrace_driver - Representation of a trace driver.
>   * @id_table:      Table to match components handled by the driver.
> + * @copyto_auxbuf: Callback to copy data into perf AUX buffer. The driver
> + *                 reports the PMU specific trace format of the copied data
> + *                 via @format (see PERF_AUX_FLAG_PMU_FORMAT_TYPE_MASK).
>   * @start:         Callback to start tracing.
>   * @stop:          Callback to stop tracing.
>   * @probe:         Driver probe() function.
> @@ -270,6 +291,9 @@ int gtrace_path_stop(struct gtrace_path *path);
>   */
>  struct gtrace_driver {
>  	const struct gtrace_component_id *id_table;
> +	size_t			(*copyto_auxbuf)(struct gtrace_component *comp,
> +						 struct gtrace_perf_auxbuf *buf,
> +						 u64 *format);
>  	int			(*start)(struct gtrace_component *comp);
>  	int			(*stop)(struct gtrace_component *comp);
>  	int			(*probe)(struct gtrace_component *comp);