Re: [PATCH] libtracefs: Add new API for open trace marker file

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 19 Feb 2021 07:53:53 +0200
"Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com> wrote:

> Added new API for opening trace_marker file of given instance:
>    tracefs_trace_marker_get_fd();
> 
> Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
> ---
>

As I wrote the perf-trace.c program, I was thinking what we really should
have is the following API. We can keep this API, but what would be nice is:


	int tracefs_print_init(struct tracefs_instance *instance);

	int tracefs_print(struct tracefs_instance *instance,
			 const char *fmt, ...);

	int tracefs_vprint(struct tracefs_instance *instance,
			   const char *fmt, va_list ap);

	void tracefs_print_reset(struct tracefs_instance *instance);

Where tracefs_print_init() will open the trace_marker for that instance
(NULL being the top level), and storing it in the instance structure.

tracefs_print() and tracefs_vprint() will check if the trace_marker file
has already been opened (tracefs_print_init() was previously called), and
if not, it will open it and keep it open. Then it will write to the
trace_marker file the passed in print data after formatting it (see my
trace_print in perf-trace.c).

The tracefs_print_reset() will simply close the trace_marker file if it was
previously opened, note, so will any of the destructors of the instance.

We could also have:

	int tracefs_raw_print_init(struct tracefs_instance *instance);

	int tracefs_raw_print(struct tracefs_instance *instance,
			  void *data, int len);

	void tracefs_raw_print_reset(struct tracefs_instance *instance);


That is the same, but instead of writing string data to the trace_marker,
it would write in memory into trace_marker_raw.

-- Steve