Re: [PATCH 5/5] tracing: New functions for kernel access to Ftrace instances

[Steven Rostedt]

On Wed, 14 Aug 2019 10:55:27 -0700
Divya Indi <divya.indi@xxxxxxxxxx> wrote:

> Adding 2 new functions -
> 1) trace_array_lookup : Look up and return a trace array, given its
> name.
> 2) trace_array_set_clr_event : Enable/disable event recording to the
> given trace array.
> 
> NOTE: trace_array_lookup returns a trace array and also increments the
> reference counter associated with the returned trace array. Make sure to
> call trace_array_put() once the use is done so that the instance can be
> removed at a later time.
> 
> Example use:
> 
> tr = trace_array_lookup("foo-bar");

Should probably be renamed to: trace_array_get_by_name("foo-bar")

As the name should show that it adds a ref count.

But if we make the change I suggested before, where we do not need to
do the put before calling the destroy, we should have:


> if (!tr)
{
> 	tr = trace_array_create("foo-bar");
	trace_array_get(tr);
}


> // Log to tr
> // Enable/disable events to tr
> trace_array_set_clr_event(tr, _THIS_IP,"system","event",1);

What's with the __THIS_IP?


> 
> // Done using tr
> trace_array_put(tr);
> ..
> 
> Also, use trace_array_set_clr_event to enable/disable events to a trace array.
> So now we no longer need to have ftrace_set_clr_event as an exported
> API.
> 
> Signed-off-by: Divya Indi <divya.indi@xxxxxxxxxx>
> ---
>  include/linux/trace.h        |  2 ++
>  include/linux/trace_events.h |  3 ++-
>  kernel/trace/trace.c         | 28 ++++++++++++++++++++++++++++
>  kernel/trace/trace_events.c  | 23 ++++++++++++++++++++++-
>  4 files changed, 54 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/trace.h b/include/linux/trace.h
> index 2c782d5..05164bb 100644
> --- a/include/linux/trace.h
> +++ b/include/linux/trace.h
> @@ -32,6 +32,8 @@ int trace_array_printk(struct trace_array *tr, unsigned long ip,
>  struct trace_array *trace_array_create(const char *name);
>  int trace_array_destroy(struct trace_array *tr);
>  void trace_array_put(struct trace_array *tr);
> +struct trace_array *trace_array_lookup(const char *name);
> +
>  #endif	/* CONFIG_TRACING */
>  
>  #endif	/* _LINUX_TRACE_H */
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 8a62731..05a7514 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -540,7 +540,8 @@ extern int trace_define_field(struct trace_event_call *call, const char *type,
>  #define is_signed_type(type)	(((type)(-1)) < (type)1)
>  
>  int trace_set_clr_event(const char *system, const char *event, int set);
> -
> +int trace_array_set_clr_event(struct trace_array *tr, const char *system,
> +		const char *event, int set);
>  /*
>   * The double __builtin_constant_p is because gcc will give us an error
>   * if we try to allocate the static variable to fmt if it is not a
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 7b6a37a..e394d55 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -8514,6 +8514,34 @@ static int instance_rmdir(const char *name)
>  	return ret;
>  }
>  
> +/**
> + * trace_array_lookup - Lookup the trace array, given its name.
> + * @name: The name of the trace array to be looked up.
> + *
> + * Lookup and return the trace array associated with @name.
> + *
> + * NOTE: The reference counter associated with the returned trace array is
> + * incremented to ensure it is not freed when in use. Make sure to call
> + * "trace_array_put" for this trace array when its use is done.
> + */
> +struct trace_array *trace_array_lookup(const char *name)
> +{
> +	struct trace_array *tr;
> +
> +	mutex_lock(&trace_types_lock);
> +
> +	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
> +		if (tr->name && strcmp(tr->name, name) == 0) {
> +			tr->ref++;
> +			mutex_unlock(&trace_types_lock);
> +			return tr;
> +		}
> +	}
> +	mutex_unlock(&trace_types_lock);
> +	return NULL;
> +}
> +EXPORT_SYMBOL_GPL(trace_array_lookup);
> +
>  static __init void create_trace_instances(struct dentry *d_tracer)
>  {
>  	trace_instance_dir = tracefs_create_instance_dir("instances", d_tracer,
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 2621995..96dd997 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -834,7 +834,6 @@ static int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set)
>  
>  	return ret;
>  }
> -EXPORT_SYMBOL_GPL(ftrace_set_clr_event);
>  
>  /**
>   * trace_set_clr_event - enable or disable an event
> @@ -859,6 +858,28 @@ int trace_set_clr_event(const char *system, const char *event, int set)
>  }
>  EXPORT_SYMBOL_GPL(trace_set_clr_event);
>  
> +/**
> + * trace_array_set_clr_event - enable or disable an event for a trace array
> + * @system: system name to match (NULL for any system)
> + * @event: event name to match (NULL for all events, within system)
> + * @set: 1 to enable, 0 to disable

We probably should make this a boolean.

-- Steve

> + *
> + * This is a way for other parts of the kernel to enable or disable
> + * event recording to instances.
> + *
> + * Returns 0 on success, -EINVAL if the parameters do not match any
> + * registered events.
> + */
> +int trace_array_set_clr_event(struct trace_array *tr, const char *system,
> +		const char *event, int set)
> +{
> +	if (!tr)
> +		return -ENOENT;
> +
> +	return __ftrace_set_clr_event(tr, NULL, system, event, set);
> +}
> +EXPORT_SYMBOL_GPL(trace_array_set_clr_event);
> +
>  /* 128 should be much more than enough */
>  #define EVENT_BUF_SIZE		127
>