1 files changed, 71 insertions, 0 deletions

diff --git a/include/linux/lockref.h b/include/linux/lockref.h
new file mode 100644
index 000000000000..01233e01627a
--- /dev/null
+++ b/include/linux/lockref.h
@@ -0,0 +1,71 @@
+#ifndef __LINUX_LOCKREF_H
+#define __LINUX_LOCKREF_H
+
+/*
+ * Locked reference counts.
+ *
+ * These are different from just plain atomic refcounts in that they
+ * are atomic with respect to the spinlock that goes with them.  In
+ * particular, there can be implementations that don't actually get
+ * the spinlock for the common decrement/increment operations, but they
+ * still have to check that the operation is done semantically as if
+ * the spinlock had been taken (using a cmpxchg operation that covers
+ * both the lock and the count word, or using memory transactions, for
+ * example).
+ */
+
+#include <linux/spinlock.h>
+
+struct lockref {
+        spinlock_t lock;
+        unsigned int count;
+};
+
+/**
+ * lockref_get - Increments reference count unconditionally
+ * @lockcnt: pointer to lockref structure
+ *
+ * This operation is only valid if you already hold a reference
+ * to the object, so you know the count cannot be zero.
+ */
+static inline void lockref_get(struct lockref *lockref)
+{
+        spin_lock(&lockref->lock);
+        lockref->count++;
+        spin_unlock(&lockref->lock);
+}
+
+/**
+ * lockref_get_not_zero - Increments count unless the count is 0
+ * @lockcnt: pointer to lockref structure
+ * Return: 1 if count updated successfully or 0 if count is 0
+ */
+static inline int lockref_get_not_zero(struct lockref *lockref)
+{
+        int retval = 0;
+
+        spin_lock(&lockref->lock);
+        if (lockref->count) {
+                lockref->count++;
+                retval = 1;
+        }
+        spin_unlock(&lockref->lock);
+        return retval;
+}
+
+/**
+ * lockref_put_or_lock - decrements count unless count <= 1 before decrement
+ * @lockcnt: pointer to lockref structure
+ * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
+ */
+static inline int lockref_put_or_lock(struct lockref *lockref)
+{
+        spin_lock(&lockref->lock);
+        if (lockref->count <= 1)
+                return 0;
+        lockref->count--;
+        spin_unlock(&lockref->lock);
+        return 1;
+}
+
+#endif /* __LINUX_LOCKREF_H */