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Subject: Re: [RFC PATCH -v2 1/4] trace events: Interface to add files to
 debugfs
From: Steven Rostedt <rostedt@goodmis.org>
To: Borislav Petkov <bp@amd64.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Borislav Petkov <borislav.petkov@amd.com>
Date: Thu, 16 Aug 2012 18:06:48 -0400
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	 <1345139123-15212-2-git-send-email-bp@amd64.org>
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On Thu, 2012-08-16 at 19:45 +0200, Borislav Petkov wrote:
> From: Borislav Petkov <borislav.petkov@amd.com>
> 
> This generic interface is supposed to be used to add files to
> (debugfs)/tracing/events/<subsys>/<event_name>/ which are supposed to
> export additional events functionality to users.
> 
> For example, the file descriptor of a persistent event can be exported
> like this in the 'pers' node:
> 
> /mnt/dbg/tracing/events/mce/mce_record/
> |-- enable
> |-- filter
> |-- format
> |-- id
> `-- persistent

This looks rather hacky :-/

Can't this be added to the perf syscall, and have the user query the
event instead?

Note, this code will change drastically soon, and this change will
break. I'll talk more about what will change at plumbers.

-- Steve

> 
> So that userspace tools can read it out and map it directly.
> 
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
> ---
>  include/linux/ftrace_event.h |  3 +++
>  kernel/trace/trace.c         |  4 ++++
>  kernel/trace/trace.h         |  1 +
>  kernel/trace/trace_events.c  | 35 +++++++++++++++++++++++++++++++++++
>  4 files changed, 43 insertions(+)
> 
> diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
> index 642928cf57b4..f4f283954cbf 100644
> --- a/include/linux/ftrace_event.h
> +++ b/include/linux/ftrace_event.h
> @@ -265,6 +265,9 @@ extern int trace_define_field(struct ftrace_event_call *call, const char *type,
>  			      int is_signed, int filter_type);
>  extern int trace_add_event_call(struct ftrace_event_call *call);
>  extern void trace_remove_event_call(struct ftrace_event_call *call);
> +extern struct dentry *
> +trace_add_file(const char *dir_name, const char *fname, umode_t mode,
> +		void *data, const struct file_operations *fops);
>  
>  #define is_signed_type(type)	(((type)(-1)) < 0)
>  
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 5c38c81496ce..e45479572328 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -4641,6 +4641,10 @@ struct dentry *trace_create_file(const char *name,
>  	return ret;
>  }
>  
> +void trace_remove_file(struct dentry *d)
> +{
> +	return debugfs_remove(d);
> +}
>  
>  static struct dentry *trace_options_init_dentry(void)
>  {
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 55e1f7f0db12..fd639f45c425 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -338,6 +338,7 @@ struct dentry *trace_create_file(const char *name,
>  				 struct dentry *parent,
>  				 void *data,
>  				 const struct file_operations *fops);
> +void trace_remove_file(struct dentry *d);
>  
>  struct dentry *tracing_init_dentry(void);
>  
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 29111da1d100..5eda4f584380 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -1199,6 +1199,41 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events,
>  	return 0;
>  }
>  
> +static struct dentry *__trace_add_file(struct ftrace_event_call *call,
> +				       const char *fname, umode_t mode,
> +				       void *data,
> +				       const struct file_operations *fops)
> +{
> +	struct dentry *ret;
> +
> +	mutex_lock(&event_mutex);
> +	ret = trace_create_file(fname, mode, call->dir, data, fops);
> +	mutex_unlock(&event_mutex);
> +
> +	return ret;
> +}
> +
> +/*
> + * Assumptions:
> + * - event debugfs dir is already initialized
> + * - trace event is not declared in a module
> + */
> +struct dentry *trace_add_file(const char *dir_name, const char *fname,
> +			      umode_t mode, void *data,
> +			      const struct file_operations *fops)
> +{
> +	struct ftrace_event_call *call;
> +
> +	if (!strlen(fname))
> +		return NULL;
> +
> +	list_for_each_entry(call, &ftrace_events, list) {
> +		if (!strncmp(call->name, dir_name, strlen(dir_name)))
> +			return __trace_add_file(call, fname, mode, data, fops);
> +	}
> +	return NULL;
> +}
> +
>  static int
>  __trace_add_event_call(struct ftrace_event_call *call, struct module *mod,
>  		       const struct file_operations *id,


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