perf header: Add is_perf_magic() func

With this function, other modules can basically check whether a file is
a legal perf data file by checking its first 8 bytes against all
possible perf magic numbers.

Change the function name from check_perf_magic to more meaningful
is_perf_magic as suggested by acme.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1351569369-26732-7-git-send-email-feng.tang@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/header.c

@@ -2341,6 +2341,16 @@ static int try_all_pipe_abis(uint64_t hdr_sz, struct perf_header *ph)
 	return -1;
 }
 
+bool is_perf_magic(u64 magic)
+{
+	if (!memcmp(&magic, __perf_magic1, sizeof(magic))
+		|| magic == __perf_magic2
+		|| magic == __perf_magic2_sw)
+		return true;
+
+	return false;
+}
+
 static int check_magic_endian(u64 magic, uint64_t hdr_sz,
 			      bool is_pipe, struct perf_header *ph)
 {

tools/perf/util/header.h

@@ -154,6 +154,7 @@ int perf_event__synthesize_build_id(struct perf_tool *tool,
 int perf_event__process_build_id(struct perf_tool *tool,
 				 union perf_event *event,
 				 struct perf_session *session);
+bool is_perf_magic(u64 magic);
 
 /*
  * arch specific callback