tracing: Use the return of str_has_prefix() to remove open coded numbers

There are several locations that compare constants to the beginning of
string variables to determine what commands should be done, then the
constant length is used to index into the string. This is error prone as the
hard coded numbers have to match the size of the constants. Instead, use the
len returned from str_has_prefix() and remove the open coded string length
sizes.

Cc: Joe Perches <joe@perches.com>
Acked-by: Masami  Hiramatsu <mhiramat@kernel.org> (for trace_probe part)
Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 9 insertions, 8 deletions

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 541375737403..9962cb5da8ac 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -186,19 +186,20 @@ int traceprobe_parse_event_name(const char **pevent, const char **pgroup,
 static int parse_probe_vars(char *arg, const struct fetch_type *t,
 			    struct fetch_insn *code, unsigned int flags)
 {
-	int ret = 0;
 	unsigned long param;
+	int ret = 0;
+	int len;
 
 	if (strcmp(arg, "retval") == 0) {
 		if (flags & TPARG_FL_RETURN)
 			code->op = FETCH_OP_RETVAL;
 		else
 			ret = -EINVAL;
-	} else if (str_has_prefix(arg, "stack")) {
-		if (arg[5] == '\0') {
+	} else if ((len = str_has_prefix(arg, "stack"))) {
+		if (arg[len] == '\0') {
 			code->op = FETCH_OP_STACKP;
-		} else if (isdigit(arg[5])) {
-			ret = kstrtoul(arg + 5, 10, &param);
+		} else if (isdigit(arg[len])) {
+			ret = kstrtoul(arg + len, 10, &param);
 			if (ret || ((flags & TPARG_FL_KERNEL) &&
 				    param > PARAM_MAX_STACK))
 				ret = -EINVAL;
@@ -213,10 +214,10 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
 #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
 	} else if (((flags & TPARG_FL_MASK) ==
 		    (TPARG_FL_KERNEL | TPARG_FL_FENTRY)) &&
-		   str_has_prefix(arg, "arg")) {
-		if (!isdigit(arg[3]))
+		   (len = str_has_prefix(arg, "arg"))) {
+		if (!isdigit(arg[len]))
 			return -EINVAL;
-		ret = kstrtoul(arg + 3, 10, &param);
+		ret = kstrtoul(arg + len, 10, &param);
 		if (ret || !param || param > PARAM_MAX_STACK)
 			return -EINVAL;
 		code->op = FETCH_OP_ARG;