tracing: Add a method to pass in trace_array descriptor to option files

In preparation of having the multi buffer instances having their own trace
option flags, the trace option files needs a way to not only pass in the
flag they represent, but also the trace_array descriptor.

A new field is added to the trace_array descriptor called trace_flags_index,
which is a 32 byte character array representing a bit. This array is simply
filled with the index of the array, where

  index_array[n] = n;

Then the address of this array is passed to the file callbacks instead of
the index of the flag index. Then to retrieve both the flag index and the
trace_array descriptor:

  data is the passed in argument.

  index = *(unsigned char *)data;

  data -= index;

  /* Now data points to the address of the array in the trace_array */

  tr = container_of(data, struct trace_array, trace_flags_index);

Suggested-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index eda4e6f8159b..423cb48a1d6d 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -168,6 +168,8 @@ struct trace_buffer {
 	int				cpu;
 };
 
+#define TRACE_FLAGS_MAX_SIZE		32
+
 /*
  * The trace array - an array of per-CPU trace arrays. This is the
  * highest level data structure that individual tracers deal with.
@@ -218,6 +220,7 @@ struct trace_array {
 	int			clock_id;
 	struct tracer		*current_trace;
 	unsigned int		trace_flags;
+	unsigned char		trace_flags_index[TRACE_FLAGS_MAX_SIZE];
 	unsigned int		flags;
 	raw_spinlock_t		start_lock;
 	struct dentry		*dir;