1 files changed, 105 insertions, 0 deletions
diff --git a/kernel/rwsem.c b/kernel/rwsem.c
new file mode 100644
index 000000000000..790a99bb25aa
--- /dev/null
+++ b/kernel/rwsem.c
@@ -0,0 +1,105 @@
+/* kernel/rwsem.c: R/W semaphores, public implementation
+ *
+ * Written by David Howells (dhowells@redhat.com).
+ * Derived from asm-i386/semaphore.h
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/rwsem.h>
+
+#include <asm/system.h>
+#include <asm/atomic.h>
+
+/*
+ * lock for reading
+ */
+void down_read(struct rw_semaphore *sem)
+{
+	might_sleep();
+	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
+
+	__down_read(sem);
+}
+
+EXPORT_SYMBOL(down_read);
+
+/*
+ * trylock for reading -- returns 1 if successful, 0 if contention
+ */
+int down_read_trylock(struct rw_semaphore *sem)
+{
+	int ret = __down_read_trylock(sem);
+
+	if (ret == 1)
+		rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
+	return ret;
+}
+
+EXPORT_SYMBOL(down_read_trylock);
+
+/*
+ * lock for writing
+ */
+void down_write(struct rw_semaphore *sem)
+{
+	might_sleep();
+	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
+
+	__down_write(sem);
+}
+
+EXPORT_SYMBOL(down_write);
+
+/*
+ * trylock for writing -- returns 1 if successful, 0 if contention
+ */
+int down_write_trylock(struct rw_semaphore *sem)
+{
+	int ret = __down_write_trylock(sem);
+
+	if (ret == 1)
+		rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
+	return ret;
+}
+
+EXPORT_SYMBOL(down_write_trylock);
+
+/*
+ * release a read lock
+ */
+void up_read(struct rw_semaphore *sem)
+{
+	rwsem_release(&sem->dep_map, 1, _RET_IP_);
+
+	__up_read(sem);
+}
+
+EXPORT_SYMBOL(up_read);
+
+/*
+ * release a write lock
+ */
+void up_write(struct rw_semaphore *sem)
+{
+	rwsem_release(&sem->dep_map, 1, _RET_IP_);
+
+	__up_write(sem);
+}
+
+EXPORT_SYMBOL(up_write);
+
+/*
+ * downgrade write lock to read lock
+ */
+void downgrade_write(struct rw_semaphore *sem)
+{
+	/*
+	 * lockdep: a downgraded write will live on as a write
+	 * dependency.
+	 */
+	__downgrade_write(sem);
+}
+
+EXPORT_SYMBOL(downgrade_write);