Re: [PATCH 1/3] Add tracing_off_event() to stop tracing when a bug or warning occur

[Steven Rostedt <rostedt@goodmis.org>]

[ Expanded the Cc list ]

On Thu, 2010-03-18 at 09:48 -0400, Chase Douglas wrote:
> The tracing_off_event() function calls tracing_off() to stop tracing
> when an event occurs. By default, only BUG-type events stop tracing,
> while WARNING type events do not. This is controlled through the
> tracing_off={none,warn,bug} commandline parameter.
> 
> Call this function from bug and warning event handlers to enable a user
> to debug their kernel by starting a trace, hitting an event, and then
> retrieving trace info knowing that the trace was stopped right after the
> event was hit.
> 
> Signed-off-by: Chase Douglas <chase.douglas@canonical.com>
> ---
>  include/linux/kernel.h     |    5 +++++
>  kernel/trace/ring_buffer.c |   34 ++++++++++++++++++++++++++++++++++
>  2 files changed, 39 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 7f07074..107091f 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -478,16 +478,21 @@ static inline char *pack_hex_byte(char *buf, u8 byte)
>   *
>   * Most likely, you want to use tracing_on/tracing_off.
>   */
> +#define TRACE_EVENT_BUG 0
> +#define TRACE_EVENT_WARN 1

This should probably be an enum.

> +
>  #ifdef CONFIG_RING_BUFFER
>  void tracing_on(void);
>  void tracing_off(void);
>  /* trace_off_permanent stops recording with no way to bring it back */
>  void tracing_off_permanent(void);
> +void tracing_off_event(long event);
>  int tracing_is_on(void);
>  #else
>  static inline void tracing_on(void) { }
>  static inline void tracing_off(void) { }
>  static inline void tracing_off_permanent(void) { }
> +static inline void tracing_off_event(long event) { }
>  static inline int tracing_is_on(void) { return 0; }
>  #endif
>  #ifdef CONFIG_TRACING
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 0287f9f..b148862 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -193,6 +193,40 @@ void tracing_off_permanent(void)
>  	set_bit(RB_BUFFERS_DISABLED_BIT, &ring_buffer_flags);
>  }
>  
> +static long tracing_event_mask = TRACE_EVENT_BUG;

That's a bad name. It does not seem to be a mask but seems to be a
control setting. Maybe call it tracing_event_off_ctrl ?

-- Steve


> +
> +/**
> + * tracing_off_event - turn off tracing depending on event type
> + *
> + * This function checks the event type to determine whether tracing should be
> + * disabled. Useful for disabling tracing on bugs or warnings.
> + */
> +void tracing_off_event(long event)
> +{
> +	if (event <= tracing_event_mask)
> +		tracing_off();
> +}
> +EXPORT_SYMBOL_GPL(tracing_off_event);
> +
> +static int __init tracing_off_event_setup(char *str)
> +{
> +	if (!strcmp("none", str))
> +		tracing_event_mask = -1;
> +	else if (!strcmp("bug", str))
> +		tracing_event_mask = TRACE_EVENT_BUG;
> +	else if (!strcmp("warn", str))
> +		tracing_event_mask = TRACE_EVENT_WARN;
> +	else
> +	{
> +		printk(KERN_NOTICE "Invalid value passed for tracing_off parameter\n");
> +		return 1;
> +	}
> +
> +	return 0;
> +}
> +
> +__setup("tracing_off=", tracing_off_event_setup);
> +
>  /**
>   * tracing_is_on - show state of ring buffers enabled
>   */