tracing: Add a way to soft disable trace events
In order to let triggers enable or disable events, we need a 'soft'
method for doing so. For example, if a function probe is added that
lets a user enable or disable events when a function is called, that
change must be done without taking locks or a mutex, and definitely
it can't sleep. But the full enabling of a tracepoint is expensive.
By adding a 'SOFT_DISABLE' flag, and converting the flags to be updated
without the protection of a mutex (using set/clear_bit()), this soft
disable flag can be used to allow critical sections to enable or disable
events from being traced (after the event has been placed into "SOFT_MODE").
Some caveats though: The comm recorder (to map pids with a comm) can not
be soft disabled (yet). If you disable an event with with a "soft"
disable and wait a while before reading the trace, the comm cache may be
replaced and you'll get a bunch of <...> for comms in the trace.
Reading the "enable" file for an event that is disabled will now give
you "0*" where the '*' denotes that the tracepoint is still active but
the event itself is "disabled".
[ fixed _BIT used in & operation : thanks to Dan Carpenter and smatch ]
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index bbf09c2..4bda044 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -413,6 +413,10 @@
* int __data_size;
* int pc;
*
+ * if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT,
+ * &ftrace_file->flags))
+ * return;
+ *
* local_save_flags(irq_flags);
* pc = preempt_count();
*
@@ -518,6 +522,10 @@
int __data_size; \
int pc; \
\
+ if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, \
+ &ftrace_file->flags)) \
+ return; \
+ \
local_save_flags(irq_flags); \
pc = preempt_count(); \
\