linux-kernel - Re: [PATCH] kernel: trace: pass export pointer as argument to ->write()

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Date:   Wed, 17 May 2017 09:43:32 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Felipe Balbi <felipe.balbi@...ux.intel.com>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Chunyan Zhang <zhang.chunyan@...aro.org>
Subject: Re: [PATCH] kernel: trace: pass export pointer as argument to
 ->write()

On Wed, 17 May 2017 11:05:54 +0300
Felipe Balbi <felipe.balbi@...ux.intel.com> wrote:

> That way, users don't need to keep a global static pointer and can
> rely on container_of() to fetch their own structure.
> 
> Signed-off-by: Felipe Balbi <felipe.balbi@...ux.intel.com>

Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve

> ---
> 
> I'm working on exposing this data over a USB peripheral controller and
> I really can't have a global pointer there.
> 
>  drivers/hwtracing/stm/ftrace.c | 6 ++++--
>  include/linux/trace.h          | 2 +-
>  kernel/trace/trace.c           | 2 +-
>  3 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hwtracing/stm/ftrace.c b/drivers/hwtracing/stm/ftrace.c
> index bd126a7c6da2..371b8333d9ae 100644
> --- a/drivers/hwtracing/stm/ftrace.c
> +++ b/drivers/hwtracing/stm/ftrace.c
> @@ -42,9 +42,11 @@ static struct stm_ftrace {
>   * @len:	length of the data packet
>   */
>  static void notrace
> -stm_ftrace_write(const void *buf, unsigned int len)
> +stm_ftrace_write(struct trace_export *export, const void *buf, unsigned int len)
>  {
> -	stm_source_write(&stm_ftrace.data, STM_FTRACE_CHAN, buf, len);
> +	struct stm_ftrace *stm = container_of(export, struct stm_ftrace, ftrace);
> +
> +	stm_source_write(stm->data, STM_FTRACE_CHAN, buf, len);
>  }
>  
>  static int stm_ftrace_link(struct stm_source_data *data)
> diff --git a/include/linux/trace.h b/include/linux/trace.h
> index 9330a58e2651..477aed6f0caa 100644
> --- a/include/linux/trace.h
> +++ b/include/linux/trace.h
> @@ -17,7 +17,7 @@
>   */
>  struct trace_export {
>  	struct trace_export __rcu	*next;
> -	void (*write)(const void *, unsigned int);
> +	void (*write)(struct trace_export *, const void *, unsigned int);
>  };
>  
>  int register_ftrace_export(struct trace_export *export);
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index c4536c449021..6a96652a3b0f 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2317,7 +2317,7 @@ trace_process_export(struct trace_export *export,
>  
>  	entry = ring_buffer_event_data(event);
>  	size = ring_buffer_event_length(event);
> -	export->write(entry, size);
> +	export->write(export, entry, size);
>  }
>  
>  static DEFINE_MUTEX(ftrace_export_lock);