tracing: add __print_flags for events

Developers have been asking for the ability in the ftrace event tracer
to display names of bits in a flags variable.

Instead of printing out c2, it would be easier to read FOO|BAR|GOO,
assuming that FOO is bit 1, BAR is bit 6 and GOO is bit 7.

Some examples where this would be useful are the state flags in a context
switch, kmalloc flags, and even permision flags in accessing files.

[
  v2 changes include:

  Frederic Weisbecker's idea of using a mask instead of bits,
  thus we can output GFP_KERNEL instead of GPF_WAIT|GFP_IO|GFP_FS.

  Li Zefan's idea of allowing the caller of __print_flags to add their
  own delimiter (or no delimiter) where we can get for file permissions
  rwx instead of r|w|x.
]

[
  v3 changes:

   Christoph Hellwig's idea of using an array instead of va_args.
]

[ Impact: better displaying of flags in trace output ]

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

2 files changed, 26 insertions, 1 deletions

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index bae51ddfabd3..4b58cf1a11c2 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -3,12 +3,23 @@
 
 #include <linux/trace_seq.h>
 #include <linux/ring_buffer.h>
-
+#include <linux/percpu.h>
 
 struct trace_array;
 struct tracer;
 struct dentry;
 
+DECLARE_PER_CPU(struct trace_seq, ftrace_event_seq);
+
+struct trace_print_flags {
+        unsigned long           mask;
+        const char              *name;
+};
+
+const char *ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
+                                   unsigned long flags,
+                                   const struct trace_print_flags *flag_array);
+
 /*
  * The trace entry - the most basic unit of tracing. This is what
  * is printed in the end as a single line in the trace output, such as:
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index b5ff2e8229ec..22c94719c569 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -87,6 +87,7 @@
  *      struct trace_seq *s = &iter->seq;
  *      struct ftrace_raw_<call> *field; <-- defined in stage 1
  *      struct trace_entry *entry;
+ *      struct trace_seq *p;
  *      int ret;
  *
  *      entry = iter->ent;
@@ -98,7 +99,9 @@
  *
  *      field = (typeof(field))entry;
  *
+ *      p = get_cpu_var(ftrace_event_seq);
  *      ret = trace_seq_printf(s, <TP_printk> "\n");
+ *      put_cpu();
  *      if (!ret)
  *              return TRACE_TYPE_PARTIAL_LINE;
  *
@@ -119,6 +122,14 @@
 #undef __get_str
 #define __get_str(field)        ((char *)__entry + __entry->__str_loc_##field)
 
+#undef __print_flags
+#define __print_flags(flag, delim, flag_array...)                       \
+        ({                                                              \
+                static const struct trace_print_flags flags[] =         \
+                        { flag_array, { -1, NULL }};                    \
+                ftrace_print_flags_seq(p, delim, flag, flags);          \
+        })
+
 #undef TRACE_EVENT
 #define TRACE_EVENT(call, proto, args, tstruct, assign, print)          \
 enum print_line_t                                                       \
@@ -127,6 +138,7 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags)	\
         struct trace_seq *s = &iter->seq;                               \
         struct ftrace_raw_##call *field;                                \
         struct trace_entry *entry;                                      \
+        struct trace_seq *p;                                            \
         int ret;                                                        \
                                                                         \
         entry = iter->ent;                                              \
@@ -138,7 +150,9 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags)	\
                                                                         \
         field = (typeof(field))entry;                                   \
                                                                         \
+        p = &get_cpu_var(ftrace_event_seq);                             \
         ret = trace_seq_printf(s, #call ": " print);                    \
+        put_cpu();                                                      \
         if (!ret)                                                       \
                 return TRACE_TYPE_PARTIAL_LINE;                         \
                                                                         \