Commit 06e0a548 authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

tracing: Do not disable tracing when reading the trace file 

When opening the "trace" file, it is no longer necessary to disable tracing.

Note, a new option is created called "pause-on-trace", when set, will cause
the trace file to emulate its original behavior.

Link: http://lkml.kernel.org/r/20200317213416.903351225@goodmis.org



Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 1039221c

Documentation/trace/ftrace.rst

+6 −0
Original line number Diff line number Diff line
@@ -1125,6 +1125,12 @@ Here are the available options: 
	the trace displays additional information about the

	latency, as described in "Latency trace format".



  pause-on-trace

	When set, opening the trace file for read, will pause

	writing to the ring buffer (as if tracing_on was set to zero).

	This simulates the original behavior of the trace file.

	When the file is closed, tracing will be enabled again.



  record-cmd

	When any event or tracer is enabled, a hook is enabled

	in the sched_switch trace point to fill comm cache

kernel/trace/trace.c

+6 −3
Original line number Diff line number Diff line
@@ -4273,8 +4273,11 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot) 
	if (trace_clocks[tr->clock_id].in_ns)

		iter->iter_flags |= TRACE_FILE_TIME_IN_NS;



	/* stop the trace while dumping if we are not opening "snapshot" */

	if (!iter->snapshot)

	/*

	 * If pause-on-trace is enabled, then stop the trace while

	 * dumping, unless this is the "snapshot" file

	 */

	if (!iter->snapshot && (tr->trace_flags & TRACE_ITER_PAUSE_ON_TRACE))

		tracing_stop_tr(tr);



	if (iter->cpu_file == RING_BUFFER_ALL_CPUS) {
@@ -4371,7 +4374,7 @@ static int tracing_release(struct inode *inode, struct file *file) 
	if (iter->trace && iter->trace->close)

		iter->trace->close(iter);



	if (!iter->snapshot)

	if (!iter->snapshot && tr->stop_count)

		/* reenable tracing if it was previously enabled */

		tracing_start_tr(tr);

kernel/trace/trace.h

+1 −0
Original line number Diff line number Diff line
@@ -1302,6 +1302,7 @@ extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf, 
		C(IRQ_INFO,		"irq-info"),		\

		C(MARKERS,		"markers"),		\

		C(EVENT_FORK,		"event-fork"),		\

		C(PAUSE_ON_TRACE,	"pause-on-trace"),	\

		FUNCTION_FLAGS					\

		FGRAPH_FLAGS					\

		STACK_FLAGS					\

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