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>

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index bae51dd..4b58cf1 100644 (file)
--- 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 b5ff2e8..22c9471 100644 (file)
--- 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;                         \
                                                                        \

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 7136420..a4840c2 100644 (file)
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -15,6 +15,9 @@
 #define EVENT_HASHSIZE 128
 
 static DECLARE_RWSEM(trace_event_mutex);
+
+DEFINE_PER_CPU(struct trace_seq, ftrace_event_seq);
+
 static struct hlist_head event_hash[EVENT_HASHSIZE] __read_mostly;
 
 static int next_event_type = __TRACE_LAST_TYPE + 1;
@@ -212,6 +215,42 @@ int trace_seq_path(struct trace_seq *s, struct path *path)
        return 0;
 }
 
+const char *
+ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
+                      unsigned long flags,
+                      const struct trace_print_flags *flag_array)
+{
+       unsigned long mask;
+       const char *str;
+       int i;
+
+       trace_seq_init(p);
+
+       for (i = 0;  flag_array[i].name && flags; i++) {
+
+               mask = flag_array[i].mask;
+               if ((flags & mask) != mask)
+                       continue;
+
+               str = flag_array[i].name;
+               flags &= ~mask;
+               if (p->len && delim)
+                       trace_seq_puts(p, delim);
+               trace_seq_puts(p, str);
+       }
+
+       /* check for left over flags */
+       if (flags) {
+               if (p->len && delim)
+                       trace_seq_puts(p, delim);
+               trace_seq_printf(p, "0x%lx", flags);
+       }
+
+       trace_seq_putc(p, 0);
+
+       return p->buffer;
+}
+
 #ifdef CONFIG_KRETPROBES
 static inline const char *kretprobed(const char *name)
 {