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Commit 2fd196ec authored by Hiraku Toyooka's avatar Hiraku Toyooka Committed by Steven Rostedt
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tracing: Replace static old_tracer check of tracer name 

Currently the trace buffer read functions use a static variable
"old_tracer" for detecting if the current tracer changes. This
was suitable for a single trace file ("trace"), but to add a
snapshot feature that will use the same function for its file,
a check against a static variable is not sufficient.

To use the output functions for two different files, instead of
storing the current tracer in a static variable, as the trace
iterator descriptor contains a pointer to the original current
tracer's name, that pointer can now be used to check if the
current tracer has changed between different reads of the trace
file.

Link: http://lkml.kernel.org/r/20121226025252.3252.9276.stgit@liselsia



Signed-off-by: default avatarHiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 5e67b51e

kernel/trace/trace.c

+9 −13
Original line number Diff line number Diff line
@@ -1948,18 +1948,20 @@ void tracing_iter_reset(struct trace_iterator *iter, int cpu) 
static void *s_start(struct seq_file *m, loff_t *pos)

{

	struct trace_iterator *iter = m->private;

	static struct tracer *old_tracer;

	int cpu_file = iter->cpu_file;

	void *p = NULL;

	loff_t l = 0;

	int cpu;



	/* copy the tracer to avoid using a global lock all around */

	/*

	 * copy the tracer to avoid using a global lock all around.

	 * iter->trace is a copy of current_trace, the pointer to the

	 * name may be used instead of a strcmp(), as iter->trace->name

	 * will point to the same string as current_trace->name.

	 */

	mutex_lock(&trace_types_lock);

	if (unlikely(old_tracer != current_trace && current_trace)) {

		old_tracer = current_trace;

	if (unlikely(current_trace && iter->trace->name != current_trace->name))

		*iter->trace = *current_trace;

	}

	mutex_unlock(&trace_types_lock);



	atomic_inc(&trace_record_cmdline_disabled);
@@ -3494,7 +3496,6 @@ tracing_read_pipe(struct file *filp, char __user *ubuf, 
		  size_t cnt, loff_t *ppos)

{

	struct trace_iterator *iter = filp->private_data;

	static struct tracer *old_tracer;

	ssize_t sret;



	/* return any leftover data */
@@ -3506,10 +3507,8 @@ tracing_read_pipe(struct file *filp, char __user *ubuf, 


	/* copy the tracer to avoid using a global lock all around */

	mutex_lock(&trace_types_lock);

	if (unlikely(old_tracer != current_trace && current_trace)) {

		old_tracer = current_trace;

	if (unlikely(current_trace && iter->trace->name != current_trace->name))

		*iter->trace = *current_trace;

	}

	mutex_unlock(&trace_types_lock);



	/*
@@ -3665,7 +3664,6 @@ static ssize_t tracing_splice_read_pipe(struct file *filp, 
		.ops		= &tracing_pipe_buf_ops,

		.spd_release	= tracing_spd_release_pipe,

	};

	static struct tracer *old_tracer;

	ssize_t ret;

	size_t rem;

	unsigned int i;
@@ -3675,10 +3673,8 @@ static ssize_t tracing_splice_read_pipe(struct file *filp, 


	/* copy the tracer to avoid using a global lock all around */

	mutex_lock(&trace_types_lock);

	if (unlikely(old_tracer != current_trace && current_trace)) {

		old_tracer = current_trace;

	if (unlikely(current_trace && iter->trace->name != current_trace->name))

		*iter->trace = *current_trace;

	}

	mutex_unlock(&trace_types_lock);



	mutex_lock(&iter->mutex);