[libcamera-devel] [RFC 08/11] libcamera: media_device: Restrict acquire() and release()

[Niklas Söderlund]

The only valid call site for acquire() and release() are inside the
PipelineHandler base class. Make them private to with a specific friend
clause to block specific pipeline handler implementations from calling
them.

Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
---
 src/libcamera/include/media_device.h        |  6 +-
 src/libcamera/media_device.cpp              | 85 +++++++++++----------
 test/v4l2_device/v4l2_device_test.cpp       |  5 --
 test/v4l2_subdevice/v4l2_subdevice_test.cpp | 10 ---
 4 files changed, 47 insertions(+), 59 deletions(-)

diff --git a/src/libcamera/include/media_device.h b/src/libcamera/include/media_device.h
index e513a2fee1b91a1b..5d28a7bb8214ef4a 100644
--- a/src/libcamera/include/media_device.h
+++ b/src/libcamera/include/media_device.h
@@ -26,8 +26,6 @@ public:
 	MediaDevice(const std::string &deviceNode);
 	~MediaDevice();
 
-	bool acquire();
-	void release();
 	bool busy() const { return acquired_; }
 
 	int populate();
@@ -62,6 +60,10 @@ private:
 	int open();
 	void close();
 
+	friend class PipelineHandler;
+	bool acquire();
+	void release();
+
 	std::map<unsigned int, MediaObject *> objects_;
 	MediaObject *object(unsigned int id);
 	bool addObject(MediaObject *object);
diff --git a/src/libcamera/media_device.cpp b/src/libcamera/media_device.cpp
index 0138be526f886c90..46931f52688f6c82 100644
--- a/src/libcamera/media_device.cpp
+++ b/src/libcamera/media_device.cpp
@@ -73,48 +73,6 @@ MediaDevice::~MediaDevice()
 	clear();
 }
 
-/**
- * \brief Claim a device for exclusive use
- *
- * The device claiming mechanism offers simple media device access arbitration
- * between multiple users. When the media device is created, it is available to
- * all users. Users can query the media graph to determine whether they can
- * support the device and, if they do, claim the device for exclusive use. Other
- * users are then expected to skip over media devices in use as reported by the
- * busy() function.
- *
- * Once claimed the device shall be released by its user when not needed anymore
- * by calling the release() function.
- *
- * Exclusive access is only guaranteed if all users of the media device abide by
- * the device claiming mechanism, as it isn't enforced by the media device
- * itself.
- *
- * \return true if the device was successfully claimed, or false if it was
- * already in use
- * \sa release(), busy()
- */
-bool MediaDevice::acquire()
-{
-	if (acquired_)
-		return false;
-
-	if (open())
-		return false;
-
-	acquired_ = true;
-	return true;
-}
-
-/**
- * \brief Release a device previously claimed for exclusive use
- * \sa acquire(), busy()
- */
-void MediaDevice::release()
-{
-	close();
-	acquired_ = false;
-}
 
 /**
  * \fn MediaDevice::busy()
@@ -420,6 +378,49 @@ void MediaDevice::close()
 	fd_ = -1;
 }
 
+/**
+ * \brief Claim a device for exclusive use
+ *
+ * The device claiming mechanism offers simple media device access arbitration
+ * between multiple users. When the media device is created, it is available to
+ * all users. Users can query the media graph to determine whether they can
+ * support the device and, if they do, claim the device for exclusive use. Other
+ * users are then expected to skip over media devices in use as reported by the
+ * busy() function.
+ *
+ * Once claimed the device shall be released by its user when not needed anymore
+ * by calling the release() function.
+ *
+ * Exclusive access is only guaranteed if all users of the media device abide by
+ * the device claiming mechanism, as it isn't enforced by the media device
+ * itself.
+ *
+ * \return true if the device was successfully claimed, or false if it was
+ * already in use
+ * \sa release(), busy()
+ */
+bool MediaDevice::acquire()
+{
+	if (acquired_)
+		return false;
+
+	if (open())
+		return false;
+
+	acquired_ = true;
+	return true;
+}
+
+/**
+ * \brief Release a device previously claimed for exclusive use
+ * \sa acquire(), busy()
+ */
+void MediaDevice::release()
+{
+	close();
+	acquired_ = false;
+}
+
 /**
  * \var MediaDevice::objects_
  * \brief Global map of media objects (entities, pads, links) keyed by their
diff --git a/test/v4l2_device/v4l2_device_test.cpp b/test/v4l2_device/v4l2_device_test.cpp
index 90e5f7a3ee0c0f2f..833038d56ea4631d 100644
--- a/test/v4l2_device/v4l2_device_test.cpp
+++ b/test/v4l2_device/v4l2_device_test.cpp
@@ -46,9 +46,6 @@ int V4L2DeviceTest::init()
 	if (!media_)
 		return TestSkip;
 
-	if (!media_->acquire())
-		return TestSkip;
-
 	MediaEntity *entity = media_->getEntityByName("vivid-000-vid-cap");
 	if (!entity)
 		return TestSkip;
@@ -62,8 +59,6 @@ int V4L2DeviceTest::init()
 
 void V4L2DeviceTest::cleanup()
 {
-	media_->release();
-
 	capture_->streamOff();
 	capture_->releaseBuffers();
 	capture_->close();
diff --git a/test/v4l2_subdevice/v4l2_subdevice_test.cpp b/test/v4l2_subdevice/v4l2_subdevice_test.cpp
index 31f3465a7ba3a5b1..0180698840cc2751 100644
--- a/test/v4l2_subdevice/v4l2_subdevice_test.cpp
+++ b/test/v4l2_subdevice/v4l2_subdevice_test.cpp
@@ -45,16 +45,9 @@ int V4L2SubdeviceTest::init()
 		return TestSkip;
 	}
 
-	if (!media_->acquire()) {
-		cerr << "Unable to acquire media device: "
-		     << media_->deviceNode() << endl;
-		return TestSkip;
-	}
-
 	MediaEntity *videoEntity = media_->getEntityByName("Scaler");
 	if (!videoEntity) {
 		cerr << "Unable to find media entity 'Scaler'" << endl;
-		media_->release();
 		return TestFail;
 	}
 
@@ -63,7 +56,6 @@ int V4L2SubdeviceTest::init()
 	if (ret) {
 		cerr << "Unable to open video subdevice "
 		     << scaler_->deviceNode() << endl;
-		media_->release();
 		return TestSkip;
 	}
 
@@ -72,7 +64,5 @@ int V4L2SubdeviceTest::init()
 
 void V4L2SubdeviceTest::cleanup()
 {
-	media_->release();
-
 	delete scaler_;
 }
-- 
2.21.0