aufs: module parameter, debug

This parameter is available only when CONFIG_AUFS_DEBUG is enabled, and
its default value is 0. Setting 1 will enable the various verifications
and debug outputs.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

fs/aufs/Makefile

@@ -8,3 +8,6 @@ ccflags-y += -include ${srctree}/include/uapi/linux/aufs_type.h
 obj-$(CONFIG_AUFS_FS) += aufs.o
 aufs-y := module.o super.o \
 	iinfo.o
+
+# all are boolean
+aufs-$(CONFIG_AUFS_DEBUG) += debug.o

fs/aufs/aufs.h

@@ -12,6 +12,14 @@
 
 #ifdef __KERNEL__
 
+#define AuStub(type, name, body, ...) \
+	static inline type name(__VA_ARGS__) { body; }
+
+#define AuStubVoid(name, ...) \
+	AuStub(void, name, , __VA_ARGS__)
+#define AuStubInt0(name, ...) \
+	AuStub(int, name, return 0, __VA_ARGS__)
+
 #include "debug.h"
 
 #include "inode.h"

fs/aufs/debug.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2005-2019 Junjiro R. Okajima
+ */
+
+/*
+ * debug print functions
+ */
+
+#include "aufs.h"
+
+/* Returns 0, or -errno.  arg is in kp->arg. */
+static int param_atomic_t_set(const char *val, const struct kernel_param *kp)
+{
+	int err, n;
+
+	err = kstrtoint(val, 0, &n);
+	if (!err) {
+		if (n > 0)
+			au_debug_on();
+		else
+			au_debug_off();
+	}
+	return err;
+}
+
+/* Returns length written or -errno.  Buffer is 4k (ie. be short!) */
+static int param_atomic_t_get(char *buffer, const struct kernel_param *kp)
+{
+	atomic_t *a;
+
+	a = kp->arg;
+	return sprintf(buffer, "%d", atomic_read(a));
+}
+
+static struct kernel_param_ops param_ops_atomic_t = {
+	.set = param_atomic_t_set,
+	.get = param_atomic_t_get
+	/* void (*free)(void *arg) */
+};
+
+atomic_t aufs_debug = ATOMIC_INIT(0);
+MODULE_PARM_DESC(debug, "debug print");
+module_param_named(debug, aufs_debug, atomic_t, 0664);

fs/aufs/debug.h

@@ -12,11 +12,35 @@
 
 #ifdef __KERNEL__
 
+#include <linux/atomic.h>
+#include <linux/module.h>
+
 #ifdef CONFIG_AUFS_DEBUG
 #define AuDebugOn(a)		BUG_ON(a)
+
+/* module parameter */
+extern atomic_t aufs_debug;
+static inline void au_debug_on(void)
+{
+	atomic_inc(&aufs_debug);
+}
+static inline void au_debug_off(void)
+{
+	atomic_dec_if_positive(&aufs_debug);
+}
+
+static inline int au_debug_test(void)
+{
+	return atomic_read(&aufs_debug) > 0;
+}
 #else
 #define AuDebugOn(a)		do {} while (0)
+AuStubVoid(au_debug_on, void)
+AuStubVoid(au_debug_off, void)
+AuStubInt0(au_debug_test, void)
 #endif /* CONFIG_AUFS_DEBUG */
 
+#define param_check_atomic_t(name, p) __param_check(name, p, atomic_t)
+
 #endif /* __KERNEL__ */
 #endif /* __AUFS_DEBUG_H__ */