param: add a free hook to kernel_param_ops.

This allows us to generalize the KPARAM_KMALLOCED flag, by calling a function
on every parameter when a module is unloaded.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Phil Carmody <ext-phil.2.carmody@nokia.com>

include/linux/moduleparam.h

@@ -36,6 +36,8 @@ struct kernel_param_ops {
 	int (*set)(const char *val, const struct kernel_param *kp);
 	/* Returns length written or -errno.  Buffer is 4k (ie. be short!) */
 	int (*get)(char *buffer, const struct kernel_param *kp);
+	/* Optional function to free kp->arg when module unloaded. */
+	void (*free)(void *arg);
 };
 
 /* Flag bits for kernel_param.flags */

kernel/params.c

@@ -399,9 +399,20 @@ static int param_array_get(char *buffer, const struct kernel_param *kp)
 	return off;
 }
 
+static void param_array_free(void *arg)
+{
+	unsigned int i;
+	const struct kparam_array *arr = arg;
+
+	if (arr->ops->free)
+		for (i = 0; i < (arr->num ? *arr->num : arr->max); i++)
+			arr->ops->free(arr->elem + arr->elemsize * i);
+}
+
 struct kernel_param_ops param_array_ops = {
 	.set = param_array_set,
 	.get = param_array_get,
+	.free = param_array_free,
 };
 EXPORT_SYMBOL(param_array_ops);
 
@@ -634,7 +645,11 @@ void module_param_sysfs_remove(struct module *mod)
 
 void destroy_params(const struct kernel_param *params, unsigned num)
 {
-	/* FIXME: This should free kmalloced charp parameters.  It doesn't. */
+	unsigned int i;
+
+	for (i = 0; i < num; i++)
+		if (params[i].ops->free)
+			params[i].ops->free(params[i].arg);
 }
 
 static void __init kernel_add_sysfs_param(const char *name,