kref: add kref structure to kernel tree.

Based on the kobject structure, but much smaller and simpler to use.

include/linux/kref.h

+/*
+ * kref.c - library routines for handling generic reference counted objects
+ *
+ * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
+ * Copyright (C) 2004 IBM Corp.
+ *
+ * based on kobject.h which was:
+ * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
+ * Copyright (C) 2002-2003 Open Source Development Labs
+ *
+ * This file is released under the GPLv2.
+ *
+ */
+
+#if defined(__KERNEL__) && !defined(_KREF_H_)
+#define _KREF_H_
+
+#include <linux/types.h>
+#include <asm/atomic.h>
+
+
+struct kref {
+	atomic_t refcount;
+	void (*release)(struct kref *kref);
+};
+
+void kref_init(struct kref *kref, void (*release)(struct kref *));
+struct kref *kref_get(struct kref *kref);
+void kref_put(struct kref *kref);
+
+
+#endif /* _KREF_H_ */

lib/Makefile

@@ -8,6 +8,9 @@ lib-y := errno.o ctype.o string.o vsprintf.o cmdline.o \
 	 kobject.o idr.o div64.o parser.o int_sqrt.o \
 	 bitmap.o extable.o
 
+# hack for now till some static code uses krefs, then it can move up above...
+obj-y += kref.o
+
 lib-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o
 lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
 

lib/kref.c

+/*
+ * kref.c - library routines for handling generic reference counted objects
+ *
+ * Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
+ * Copyright (C) 2004 IBM Corp.
+ *
+ * based on lib/kobject.c which was:
+ * Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
+ *
+ * This file is released under the GPLv2.
+ *
+ */
+
+/* #define DEBUG */
+
+#include <linux/kref.h>
+#include <linux/module.h>
+
+/**
+ * kref_init - initialize object.
+ * @kref: object in question.
+ * @release: pointer to a function that will clean up the object
+ *	     when the last reference to the object is released.
+ *	     This pointer is required.
+ */
+void kref_init(struct kref *kref, void (*release)(struct kref *kref))
+{
+	WARN_ON(release == NULL);
+	atomic_set(&kref->refcount,1);
+	kref->release = release;
+}
+
+/**
+ * kref_get - increment refcount for object.
+ * @kref: object.
+ */
+struct kref *kref_get(struct kref *kref)
+{
+	WARN_ON(!atomic_read(&kref->refcount));
+	atomic_inc(&kref->refcount);
+	return kref;
+}
+
+/**
+ * kref_put - decrement refcount for object.
+ * @kref: object.
+ *
+ * Decrement the refcount, and if 0, call kref->release().
+ */
+void kref_put(struct kref *kref)
+{
+	if (atomic_dec_and_test(&kref->refcount)) {
+		pr_debug("kref cleaning up\n");
+		kref->release(kref);
+	}
+}
+
+EXPORT_SYMBOL(kref_init);
+EXPORT_SYMBOL(kref_get);
+EXPORT_SYMBOL(kref_put);