params: make dashes and underscores in parameter names truly equal

The user may use "foo-bar" for a kernel parameter defined as "foo_bar".
Make sure it works the other way around too.

Apply the equality of dashes and underscores on early_params and __setup
params as well.

The example given in Documentation/kernel-parameters.txt indicates that
this is the intended behaviour.

With the patch the kernel accepts "log-buf-len=1M" as expected.
https://bugzilla.redhat.com/show_bug.cgi?id=744545

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (neatened implementations)

include/linux/moduleparam.h

@@ -262,6 +262,26 @@ static inline void __kernel_param_unlock(void)
 			    .str = &__param_string_##name, 0, perm);	\
 	__MODULE_PARM_TYPE(name, "string")
 
+/**
+ * parameq - checks if two parameter names match
+ * @name1: parameter name 1
+ * @name2: parameter name 2
+ *
+ * Returns true if the two parameter names are equal.
+ * Dashes (-) are considered equal to underscores (_).
+ */
+extern bool parameq(const char *name1, const char *name2);
+
+/**
+ * parameqn - checks if two parameter names match
+ * @name1: parameter name 1
+ * @name2: parameter name 2
+ * @n: the length to compare
+ *
+ * Similar to parameq(), except it compares @n characters.
+ */
+extern bool parameqn(const char *name1, const char *name2, size_t n);
+
 /* Called on module insert or kernel boot */
 extern int parse_args(const char *name,
 		      char *args,

init/main.c

@@ -163,7 +163,7 @@ static int __init obsolete_checksetup(char *line)
 	p = __setup_start;
 	do {
 		int n = strlen(p->str);
-		if (!strncmp(line, p->str, n)) {
+		if (parameqn(line, p->str, n)) {
 			if (p->early) {
 				/* Already done in parse_early_param?
 				 * (Needs exact match on param part).
@@ -392,7 +392,7 @@ static int __init do_early_param(char *param, char *val)
 	const struct obs_kernel_param *p;
 
 	for (p = __setup_start; p < __setup_end; p++) {
-		if ((p->early && strcmp(param, p->str) == 0) ||
+		if ((p->early && parameq(param, p->str)) ||
 		    (strcmp(param, "console") == 0 &&
 		     strcmp(p->str, "earlycon") == 0)
 		) {

kernel/params.c

@@ -67,20 +67,27 @@ static void maybe_kfree_parameter(void *param)
 	}
 }
 
-static inline char dash2underscore(char c)
+static char dash2underscore(char c)
 {
 	if (c == '-')
 		return '_';
 	return c;
 }
 
-static inline int parameq(const char *input, const char *paramname)
+bool parameqn(const char *a, const char *b, size_t n)
 {
-	unsigned int i;
-	for (i = 0; dash2underscore(input[i]) == paramname[i]; i++)
-		if (input[i] == '\0')
-			return 1;
-	return 0;
+	size_t i;
+
+	for (i = 0; i < n; i++) {
+		if (dash2underscore(a[i]) != dash2underscore(b[i]))
+			return false;
+	}
+	return true;
+}
+
+bool parameq(const char *a, const char *b)
+{
+	return parameqn(a, b, strlen(a)+1);
 }
 
 static int parse_one(char *param,