ftrace: Use counters to enable functions to trace

Every function has its own record that stores the instruction
pointer and flags for the function to be traced. There are only
two flags: enabled and free. The enabled flag states that tracing
for the function has been enabled (actively traced), and the free
flag states that the record no longer points to a function and can
be used by new functions (loaded modules).

These flags are now moved to the MSB of the flags (actually just
the top 32bits). The rest of the bits (30 bits) are now used as
a ref counter. Everytime a tracer register functions to trace,
those functions will have its counter incremented.

When tracing is enabled, to determine if a function should be traced,
the counter is examined, and if it is non-zero it is set to trace.

When a ftrace_ops is registered to trace functions, its hashes
are examined. If the ftrace_ops filter_hash count is zero, then
all functions are set to be traced, otherwise only the functions
in the hash are to be traced. The exception to this is if a function
is also in the ftrace_ops notrace_hash. Then that function's counter
is not incremented for this ftrace_ops.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 6658a51390fe..ab1c46e70bb6 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -37,6 +37,7 @@ struct ftrace_ops {
 #ifdef CONFIG_DYNAMIC_FTRACE
         struct ftrace_hash              *notrace_hash;
         struct ftrace_hash              *filter_hash;
+        unsigned long                   flags;
 #endif
 };
 
@@ -152,10 +153,13 @@ extern void unregister_ftrace_function_probe_all(char *glob);
 extern int ftrace_text_reserved(void *start, void *end);
 
 enum {
-        FTRACE_FL_FREE          = (1 << 0),
-        FTRACE_FL_ENABLED       = (1 << 1),
+        FTRACE_FL_ENABLED       = (1 << 30),
+        FTRACE_FL_FREE          = (1 << 31),
 };
 
+#define FTRACE_FL_MASK          (0x3UL << 30)
+#define FTRACE_REF_MAX          ((1 << 30) - 1)
+
 struct dyn_ftrace {
         union {
                 unsigned long           ip; /* address of mcount call-site */