1 files changed, 67 insertions, 3 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 79fdd80a42d4..2dac79c39199 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -486,6 +486,8 @@ enum ftrace_dump_mode {
 void tracing_on(void);
 void tracing_off(void);
 int tracing_is_on(void);
+void tracing_snapshot(void);
+void tracing_snapshot_alloc(void);
 
 extern void tracing_start(void);
 extern void tracing_stop(void);
@@ -515,10 +517,32 @@ do {									\
  *
  * This is intended as a debugging tool for the developer only.
  * Please refrain from leaving trace_printks scattered around in
- * your code.
+ * your code. (Extra memory is used for special buffers that are
+ * allocated when trace_printk() is used)
+ *
+ * A little optization trick is done here. If there's only one
+ * argument, there's no need to scan the string for printf formats.
+ * The trace_puts() will suffice. But how can we take advantage of
+ * using trace_puts() when trace_printk() has only one argument?
+ * By stringifying the args and checking the size we can tell
+ * whether or not there are args. __stringify((__VA_ARGS__)) will
+ * turn into "()\0" with a size of 3 when there are no args, anything
+ * else will be bigger. All we need to do is define a string to this,
+ * and then take its size and compare to 3. If it's bigger, use
+ * do_trace_printk() otherwise, optimize it to trace_puts(). Then just
+ * let gcc optimize the rest.
  */
 
-#define trace_printk(fmt, args...)                                      \
+#define trace_printk(fmt, ...)                          \
+do {                                                    \
+        char _______STR[] = __stringify((__VA_ARGS__)); \
+        if (sizeof(_______STR) > 3)                     \
+                do_trace_printk(fmt, ##__VA_ARGS__);    \
+        else                                            \
+                trace_puts(fmt);                        \
+} while (0)
+
+#define do_trace_printk(fmt, args...)                                   \
 do {                                                                    \
         static const char *trace_printk_fmt                             \
                 __attribute__((section("__trace_printk_fmt"))) =        \
@@ -538,7 +562,45 @@ int __trace_bprintk(unsigned long ip, const char *fmt, ...);
 extern __printf(2, 3)
 int __trace_printk(unsigned long ip, const char *fmt, ...);
 
-extern void trace_dump_stack(void);
+/**
+ * trace_puts - write a string into the ftrace buffer
+ * @str: the string to record
+ *
+ * Note: __trace_bputs is an internal function for trace_puts and
+ *       the @ip is passed in via the trace_puts macro.
+ *
+ * This is similar to trace_printk() but is made for those really fast
+ * paths that a developer wants the least amount of "Heisenbug" affects,
+ * where the processing of the print format is still too much.
+ *
+ * This function allows a kernel developer to debug fast path sections
+ * that printk is not appropriate for. By scattering in various
+ * printk like tracing in the code, a developer can quickly see
+ * where problems are occurring.
+ *
+ * This is intended as a debugging tool for the developer only.
+ * Please refrain from leaving trace_puts scattered around in
+ * your code. (Extra memory is used for special buffers that are
+ * allocated when trace_puts() is used)
+ *
+ * Returns: 0 if nothing was written, positive # if string was.
+ *  (1 when __trace_bputs is used, strlen(str) when __trace_puts is used)
+ */
+
+extern int __trace_bputs(unsigned long ip, const char *str);
+extern int __trace_puts(unsigned long ip, const char *str, int size);
+#define trace_puts(str) ({                                              \
+        static const char *trace_printk_fmt                             \
+                __attribute__((section("__trace_printk_fmt"))) =        \
+                __builtin_constant_p(str) ? str : NULL;                 \
+                                                                        \
+        if (__builtin_constant_p(str))                                  \
+                __trace_bputs(_THIS_IP_, trace_printk_fmt);             \
+        else                                                            \
+                __trace_puts(_THIS_IP_, str, strlen(str));              \
+})
+
+extern void trace_dump_stack(int skip);
 
 /*
  * The double __builtin_constant_p is because gcc will give us an error
@@ -573,6 +635,8 @@ static inline void trace_dump_stack(void) { }
 static inline void tracing_on(void) { }
 static inline void tracing_off(void) { }
 static inline int tracing_is_on(void) { return 0; }
+static inline void tracing_snapshot(void) { }
+static inline void tracing_snapshot_alloc(void) { }
 
 static inline __printf(1, 2)
 int trace_printk(const char *fmt, ...)