ftrace: Simplify ftrace_match_record() even more

rostedt · rostedt · commit 77c0eddeeeee · 2017-05-03T22:15:13.000-04:00
Dan Carpenter sent a patch to remove a check in ftrace_match_record()
because the logic of the code made the check redundant. I looked deeper into
the code, and made the following logic table, with the three variables and
the result of the original code.

modname        mod_matches     exclude_mod         result
-------        -----------     -----------         ------
  0                 0               0              return 0
  0                 0               1              func_match
  0                 1               *             &lt; cannot exist &gt;
  1                 0               0              return 0
  1                 0               1              func_match
  1                 1               0              func_match
  1                 1               1              return 0

Notice that when mod_matches == exclude mod, the result is always to
return 0, and when mod_matches != exclude_mod, then the result is to test
the function. This means we only need test if mod_matches is equal to
exclude_mod.

Cc: Dan Carpenter &lt;dan.carpenter@oracle.com&gt;
Signed-off-by: Steven Rostedt (VMware) &lt;rostedt@goodmis.org&gt;
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
@@ -3631,22 +3631,20 @@ ftrace_match_record(struct dyn_ftrace *rec, struct ftrace_glob *func_g,
 		/* blank module name to match all modules */
 		if (!mod_g->len) {
 			/* blank module globbing: modname xor exclude_mod */
-			if ((!exclude_mod) != (!modname))
+			if (!exclude_mod != !modname)
 				goto func_match;
 			return 0;
 		}
 
-		/* not matching the module */
-		if (!modname || !mod_matches) {
-			if (exclude_mod)
-				goto func_match;
-			else
-				return 0;
-		}
-
-		if (exclude_mod)
+		/*
+		 * exclude_mod is set to trace everything but the given
+		 * module. If it is set and the module matches, then
+		 * return 0. If it is not set, and the module doesn't match
+		 * also return 0. Otherwise, check the function to see if
+		 * that matches.
+		 */
+		if (!mod_matches == !exclude_mod)
 			return 0;
-
 func_match:
 		/* blank search means to match all funcs in the mod */
 		if (!func_g->len)
