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From:   Tao Zhou <tao.zhou@linux.dev>
To:     Daniel Bristot de Oliveira <bristot@kernel.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Tom Zanussi <zanussi@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Clark Williams <williams@redhat.com>,
        John Kacur <jkacur@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Tao Zhou <tao.zhou@linux.dev>, linux-rt-users@vger.kernel.org,
        linux-trace-devel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V8 02/14] rtla: Helper functions for rtla
Message-ID: <YaneZTnR+leNRzNN@geo.homenetwork>
References: <cover.1638182284.git.bristot@kernel.org>
 <8fbb0e5ab5b39ba3c981fc97a3f93471d291cffc.1638182284.git.bristot@kernel.org>
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On Mon, Nov 29, 2021 at 12:07:40PM +0100,
Daniel Bristot de Oliveira wrote:

> +/*
> + * enable_tracer_by_name - enable a tracer on the given instance
> + */
> +int enable_tracer_by_name(struct tracefs_instance *inst, const char *tracer)
> +{ 
> +	enum tracefs_tracers t;
> +	int retval;
> +
> +	t = TRACEFS_TRACER_CUSTOM;
> +
> +	debug_msg("enabling %s tracer\n", tracer);
> +
> +	retval = tracefs_tracer_set(inst, t, tracer);

The comment of parameters used for tracefs_tracer_set() says:

'
 * tracefs_set_tracer - function to set the tracer
 * @instance: ftrace instance, can be NULL for top tracing instance
 * @tracer: The tracer enum that defines the tracer to be set
 * @t: A tracer name if TRACEFS_TRACER_CUSTOM is passed in for @tracer
'

tracefs_tracer_set(inst, tracer, t); @tracer is enum and @t is tracer
name. this is not important.

> +	if (retval < 0) {
> +		if (errno == ENODEV)
> +			err_msg("tracer %s not found!\n", tracer);
> +
> +		err_msg("failed to enable the tracer %s\n", tracer);
> +		return -1;
> +	}
> +
> +	return 0;
> +}