From: Lennart Poettering <lennart@poettering.net>
Date: Tue, 19 Nov 2013 00:15:31 +0000 (+0100)
Subject: libudev: always return NULL in _unref() APIs
X-Git-Tag: v209~1389
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=commitdiff_plain;h=725d7e6cebcafef3bd4adbf76c8fa73a9b18972e

libudev: always return NULL in _unref() APIs

Returning anything else but NULL would suggest the caller's reference
might still be valid, but it isn't, because the caller just invoked
_unref() after all.

This turns the return value into a typesafe shortcut that allows
unreffing and resetting a reference in one line. In contrast to
solutions for this which take a pointer to a pointer to accomplish the
same this solution is just syntactic sugar the developer can make use of
but doesn't have to, and this is particularly useful when immediately
unreffing objects returned by function calls.
---

diff --git a/src/libudev/libudev-device.c b/src/libudev/libudev-device.c
index b5b07fc5d..059a59060 100644
--- a/src/libudev/libudev-device.c
+++ b/src/libudev/libudev-device.c
@@ -1090,7 +1090,7 @@ _public_ struct udev_device *udev_device_ref(struct udev_device *udev_device)
  * Drop a reference of a udev device. If the refcount reaches zero,
  * the resources of the device will be released.
  *
- * Returns: the passed udev device if it has still an active reference, or #NULL otherwise.
+ * Returns: #NULL
  **/
 _public_ struct udev_device *udev_device_unref(struct udev_device *udev_device)
 {
@@ -1098,7 +1098,7 @@ _public_ struct udev_device *udev_device_unref(struct udev_device *udev_device)
                 return NULL;
         udev_device->refcount--;
         if (udev_device->refcount > 0)
-                return udev_device;
+                return NULL;
         if (udev_device->parent_device != NULL)
                 udev_device_unref(udev_device->parent_device);
         free(udev_device->syspath);
diff --git a/src/libudev/libudev-enumerate.c b/src/libudev/libudev-enumerate.c
index e71d766c0..48ffe83d3 100644
--- a/src/libudev/libudev-enumerate.c
+++ b/src/libudev/libudev-enumerate.c
@@ -122,7 +122,7 @@ _public_ struct udev_enumerate *udev_enumerate_ref(struct udev_enumerate *udev_e
  * Drop a reference of an enumeration context. If the refcount reaches zero,
  * all resources of the enumeration context will be released.
  *
- * Returns: the passed enumeration context if it has still an active reference, or #NULL otherwise.
+ * Returns: #NULL
  **/
 _public_ struct udev_enumerate *udev_enumerate_unref(struct udev_enumerate *udev_enumerate)
 {
@@ -132,7 +132,7 @@ _public_ struct udev_enumerate *udev_enumerate_unref(struct udev_enumerate *udev
                 return NULL;
         udev_enumerate->refcount--;
         if (udev_enumerate->refcount > 0)
-                return udev_enumerate;
+                return NULL;
         udev_list_cleanup(&udev_enumerate->sysattr_match_list);
         udev_list_cleanup(&udev_enumerate->sysattr_nomatch_list);
         udev_list_cleanup(&udev_enumerate->subsystem_match_list);
diff --git a/src/libudev/libudev-hwdb.c b/src/libudev/libudev-hwdb.c
index de1cb8318..b53b35ce4 100644
--- a/src/libudev/libudev-hwdb.c
+++ b/src/libudev/libudev-hwdb.c
@@ -334,14 +334,14 @@ _public_ struct udev_hwdb *udev_hwdb_ref(struct udev_hwdb *hwdb) {
  * Drop a reference of a hwdb context. If the refcount reaches zero,
  * all resources of the hwdb context will be released.
  *
- * Returns: the passed hwdb context if it has still an active reference, or #NULL otherwise.
+ * Returns: #NULL
  **/
 _public_ struct udev_hwdb *udev_hwdb_unref(struct udev_hwdb *hwdb) {
         if (!hwdb)
                 return NULL;
         hwdb->refcount--;
         if (hwdb->refcount > 0)
-                return hwdb;
+                return NULL;
         if (hwdb->map)
                 munmap((void *)hwdb->map, hwdb->st.st_size);
         if (hwdb->f)
diff --git a/src/libudev/libudev-monitor.c b/src/libudev/libudev-monitor.c
index 24efdc65e..56a6c5e39 100644
--- a/src/libudev/libudev-monitor.c
+++ b/src/libudev/libudev-monitor.c
@@ -408,7 +408,7 @@ _public_ struct udev_monitor *udev_monitor_ref(struct udev_monitor *udev_monitor
  * the bound socket will be closed, and the resources of the monitor
  * will be released.
  *
- * Returns: the passed udev monitor if it has still an active reference, or #NULL otherwise.
+ * Returns: #NULL
  **/
 _public_ struct udev_monitor *udev_monitor_unref(struct udev_monitor *udev_monitor)
 {
@@ -416,7 +416,7 @@ _public_ struct udev_monitor *udev_monitor_unref(struct udev_monitor *udev_monit
                 return NULL;
         udev_monitor->refcount--;
         if (udev_monitor->refcount > 0)
-                return udev_monitor;
+                return NULL;
         if (udev_monitor->sock >= 0)
                 close(udev_monitor->sock);
         udev_list_cleanup(&udev_monitor->filter_subsystem_list);
diff --git a/src/libudev/libudev-queue.c b/src/libudev/libudev-queue.c
index 0dd20313d..f67dba995 100644
--- a/src/libudev/libudev-queue.c
+++ b/src/libudev/libudev-queue.c
@@ -101,7 +101,7 @@ _public_ struct udev_queue *udev_queue_ref(struct udev_queue *udev_queue)
  * Drop a reference of a udev queue context. If the refcount reaches zero,
  * the resources of the queue context will be released.
  *
- * Returns: the passed queue context if it has still an active reference, or #NULL otherwise.
+ * Returns: #NULL
  **/
 _public_ struct udev_queue *udev_queue_unref(struct udev_queue *udev_queue)
 {
@@ -109,7 +109,7 @@ _public_ struct udev_queue *udev_queue_unref(struct udev_queue *udev_queue)
                 return NULL;
         udev_queue->refcount--;
         if (udev_queue->refcount > 0)
-                return udev_queue;
+                return NULL;
         udev_list_cleanup(&udev_queue->queue_list);
         free(udev_queue);
         return NULL;