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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: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (VMware) 2020-03-17 17:32:31 -04:00
parent 1039221cc2
commit 06e0a548ba
3 changed files with 13 additions and 3 deletions
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6
Documentation/trace/ftrace.rst
View File

@ -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

9
kernel/trace/trace.c
View File

@ -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);

1
kernel/trace/trace.h
View File

@ -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 \