2 files changed, 91 insertions, 0 deletions

diff --git a/fs/char_dev.c b/fs/char_dev.c
index 44a240c4bb65..fb8507f521b2 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -471,6 +471,85 @@ int cdev_add(struct cdev *p, dev_t dev, unsigned count)
         return 0;
 }
 
+/**
+ * cdev_set_parent() - set the parent kobject for a char device
+ * @p: the cdev structure
+ * @kobj: the kobject to take a reference to
+ *
+ * cdev_set_parent() sets a parent kobject which will be referenced
+ * appropriately so the parent is not freed before the cdev. This
+ * should be called before cdev_add.
+ */
+void cdev_set_parent(struct cdev *p, struct kobject *kobj)
+{
+        WARN_ON(!kobj->state_initialized);
+        p->kobj.parent = kobj;
+}
+
+/**
+ * cdev_device_add() - add a char device and it's corresponding
+ *      struct device, linkink
+ * @dev: the device structure
+ * @cdev: the cdev structure
+ *
+ * cdev_device_add() adds the char device represented by @cdev to the system,
+ * just as cdev_add does. It then adds @dev to the system using device_add
+ * The dev_t for the char device will be taken from the struct device which
+ * needs to be initialized first. This helper function correctly takes a
+ * reference to the parent device so the parent will not get released until
+ * all references to the cdev are released.
+ *
+ * This helper uses dev->devt for the device number. If it is not set
+ * it will not add the cdev and it will be equivalent to device_add.
+ *
+ * This function should be used whenever the struct cdev and the
+ * struct device are members of the same structure whose lifetime is
+ * managed by the struct device.
+ *
+ * NOTE: Callers must assume that userspace was able to open the cdev and
+ * can call cdev fops callbacks at any time, even if this function fails.
+ */
+int cdev_device_add(struct cdev *cdev, struct device *dev)
+{
+        int rc = 0;
+
+        if (dev->devt) {
+                cdev_set_parent(cdev, &dev->kobj);
+
+                rc = cdev_add(cdev, dev->devt, 1);
+                if (rc)
+                        return rc;
+        }
+
+        rc = device_add(dev);
+        if (rc)
+                cdev_del(cdev);
+
+        return rc;
+}
+
+/**
+ * cdev_device_del() - inverse of cdev_device_add
+ * @dev: the device structure
+ * @cdev: the cdev structure
+ *
+ * cdev_device_del() is a helper function to call cdev_del and device_del.
+ * It should be used whenever cdev_device_add is used.
+ *
+ * If dev->devt is not set it will not remove the cdev and will be equivalent
+ * to device_del.
+ *
+ * NOTE: This guarantees that associated sysfs callbacks are not running
+ * or runnable, however any cdevs already open will remain and their fops
+ * will still be callable even after this function returns.
+ */
+void cdev_device_del(struct cdev *cdev, struct device *dev)
+{
+        device_del(dev);
+        if (dev->devt)
+                cdev_del(cdev);
+}
+
 static void cdev_unmap(dev_t dev, unsigned count)
 {
         kobj_unmap(cdev_map, dev, count);
@@ -482,6 +561,10 @@ static void cdev_unmap(dev_t dev, unsigned count)
  *
  * cdev_del() removes @p from the system, possibly freeing the structure
  * itself.
+ *
+ * NOTE: This guarantees that cdev device will no longer be able to be
+ * opened, however any cdevs already open will remain and their fops will
+ * still be callable even after cdev_del returns.
  */
 void cdev_del(struct cdev *p)
 {
@@ -570,5 +653,8 @@ EXPORT_SYMBOL(cdev_init);
 EXPORT_SYMBOL(cdev_alloc);
 EXPORT_SYMBOL(cdev_del);
 EXPORT_SYMBOL(cdev_add);
+EXPORT_SYMBOL(cdev_set_parent);
+EXPORT_SYMBOL(cdev_device_add);
+EXPORT_SYMBOL(cdev_device_del);
 EXPORT_SYMBOL(__register_chrdev);
 EXPORT_SYMBOL(__unregister_chrdev);
diff --git a/include/linux/cdev.h b/include/linux/cdev.h
index f8763615a5f2..408bc09ce497 100644
--- a/include/linux/cdev.h
+++ b/include/linux/cdev.h
@@ -4,6 +4,7 @@
 #include <linux/kobject.h>
 #include <linux/kdev_t.h>
 #include <linux/list.h>
+#include <linux/device.h>
 
 struct file_operations;
 struct inode;
@@ -26,6 +27,10 @@ void cdev_put(struct cdev *p);
 
 int cdev_add(struct cdev *, dev_t, unsigned);
 
+void cdev_set_parent(struct cdev *p, struct kobject *kobj);
+int cdev_device_add(struct cdev *cdev, struct device *dev);
+void cdev_device_del(struct cdev *cdev, struct device *dev);
+
 void cdev_del(struct cdev *);
 
 void cd_forget(struct inode *);