[patch] Add kref_read and kref_put_last primitives

[Ravikiran G Thirumalai <kiran@in.ibm.com>]

Greg,
Here is a patch to add kref_read and kref_put_last.
These primitives were needed to change files_struct.f_count
refcounter to use kref api.

kref_put_last is needed sometimes when a refcount might
have an unconventional release which needs more than
the refcounted object to process object release-- like in the
files_struct.f_count conversion patch at __aio_put_req().
The following patch depends on kref shrinkage patches.
(which you have already included).

Please include.

Thanks,
Kiran

Signed-off-by: Ravikiran Thirumalai <kiran@in.ibm.com>

diff -ruN -X dontdiff2 linux-kref-2.6.7/include/linux/kref.h files_struct-kref-2.6.7/include/linux/kref.h
--- linux-kref-2.6.7/include/linux/kref.h	2004-07-26 18:53:24.000000000 +0530
+++ files_struct-kref-2.6.7/include/linux/kref.h	2004-07-26 18:48:43.543549752 +0530
@@ -26,6 +26,8 @@
 void kref_init(struct kref *kref);
 struct kref *kref_get(struct kref *kref);
 void kref_put(struct kref *kref, void (*release) (struct kref *kref));
+int kref_read(struct kref *kref);
+int kref_put_last(struct kref *kref);
 
 
 #endif /* _KREF_H_ */
diff -ruN -X dontdiff2 linux-kref-2.6.7/lib/kref.c files_struct-kref-2.6.7/lib/kref.c
--- linux-kref-2.6.7/lib/kref.c	2004-07-26 18:53:24.228879096 +0530
+++ files_struct-kref-2.6.7/lib/kref.c	2004-07-26 19:02:20.782310576 +0530
@@ -54,6 +54,33 @@
 	}
 }
 
+/**
+ * kref_read - Return the refcount value.
+ * @kref: object.
+ */
+int kref_read(struct kref *kref)
+{
+	return atomic_read(&kref->refcount);
+}
+
+/**
+ * kref_put_last - decrement refcount for object.
+ * @kref: object.
+ *
+ * Decrement the refcount, and if 0 return true.
+ * Returns false otherwise.  
+ * Use this only if you cannot use kref_put -- when the 
+ * release function of kref_put needs more than just the 
+ * refcounted object. Use of kref_put_last when kref_put
+ * can do will be frowned upon.
+ */
+int kref_put_last(struct kref *kref)
+{
+	return atomic_dec_and_test(&kref->refcount);
+}
+
 EXPORT_SYMBOL(kref_init);
 EXPORT_SYMBOL(kref_get);
 EXPORT_SYMBOL(kref_put);
+EXPORT_SYMBOL(kref_read);
+EXPORT_SYMBOL(kref_put_last);