linux-kernel - Re: [PATCH v2 2/6] tracing: add flag to control different traces

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Date:   Mon, 27 Jul 2020 14:45:50 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Tingwei Zhang <tingwei@...eaurora.org>
Cc:     Ingo Molnar <mingo@...hat.com>, tsoni@...eaurora.org,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Mao Jinlong <jinlmao@...eaurora.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/6] tracing: add flag to control different traces

On Sun, 26 Jul 2020 10:59:27 +0800
Tingwei Zhang <tingwei@...eaurora.org> wrote:


> diff --git a/include/linux/trace.h b/include/linux/trace.h
> index 7fd86d3c691f..d2fdf9be84b5 100644
> --- a/include/linux/trace.h
> +++ b/include/linux/trace.h
> @@ -3,6 +3,9 @@
>  #define _LINUX_TRACE_H
>  
>  #ifdef CONFIG_TRACING
> +
> +#define TRACE_EXPORT_FUNCTION	BIT_ULL(0)

All the flags variables below are defined as "int". Why the BIT_ULL()?
BIT(0) should work just fine. The ULL makes one think these flags will
be used for unsigned long variables, which it is not.

-- Steve


> +

>  struct trace_export {
>  	struct trace_export __rcu	*next;
>  	void (*write)(struct trace_export *, const void *, unsigned int);
> +	int flags;
>  };
>  
>  int register_ftrace_export(struct trace_export *export);
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index bb62269724d5..8f1e66831e9e 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2747,33 +2747,37 @@ trace_buffer_unlock_commit_nostack(struct trace_buffer *buffer,
>  
>  static void
>  trace_process_export(struct trace_export *export,
> -	       struct ring_buffer_event *event)
> +	       struct ring_buffer_event *event, int flag)
>  {
>  	struct trace_entry *entry;
>  	unsigned int size = 0;
>  
> -	entry = ring_buffer_event_data(event);
> -	size = ring_buffer_event_length(event);
> -	export->write(export, entry, size);
> +	if (export->flags & flag) {
> +		entry = ring_buffer_event_data(event);
> +		size = ring_buffer_event_length(event);
> +		export->write(export, entry, size);
> +	}
>  }