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-rw-r--r--src/libcamera/include/media_device.h5
-rw-r--r--src/libcamera/media_device.cpp50
2 files changed, 54 insertions, 1 deletions
diff --git a/src/libcamera/include/media_device.h b/src/libcamera/include/media_device.h
index d787be39..3fcdb4b4 100644
--- a/src/libcamera/include/media_device.h
+++ b/src/libcamera/include/media_device.h
@@ -24,6 +24,10 @@ public:
MediaDevice(const std::string &devnode);
~MediaDevice();
+ bool acquire();
+ void release() { acquired_ = false; }
+ bool busy() const { return acquired_; }
+
int open();
void close();
@@ -41,6 +45,7 @@ private:
std::string devnode_;
int fd_;
bool valid_;
+ bool acquired_;
std::map<unsigned int, MediaObject *> objects_;
MediaObject *object(unsigned int id);
diff --git a/src/libcamera/media_device.cpp b/src/libcamera/media_device.cpp
index 1bd4f43a..73a866bb 100644
--- a/src/libcamera/media_device.cpp
+++ b/src/libcamera/media_device.cpp
@@ -53,6 +53,10 @@ namespace libcamera {
* This will not invalidate the media graph and all cached media objects remain
* valid and can be accessed normally. The device can then be later reopened if
* needed to perform other operations that interact with the device node.
+ *
+ * Media device can be claimed for exclusive use with acquire(), released with
+ * release() and tested with busy(). This mechanism is aimed at pipeline
+ * managers to claim media devices they support during enumeration.
*/
/**
@@ -63,7 +67,7 @@ namespace libcamera {
* populated with open() and populate() before the media graph can be queried.
*/
MediaDevice::MediaDevice(const std::string &devnode)
- : devnode_(devnode), fd_(-1), valid_(false)
+ : devnode_(devnode), fd_(-1), valid_(false), acquired_(false)
{
}
@@ -75,6 +79,50 @@ MediaDevice::~MediaDevice()
}
/**
+ * \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;
+
+ acquired_ = true;
+ return true;
+}
+
+/**
+ * \fn MediaDevice::release()
+ * \brief Release a device previously claimed for exclusive use
+ * \sa acquire(), busy()
+ */
+
+/**
+ * \fn MediaDevice::busy()
+ * \brief Check if a device is in use
+ * \return true if the device has been claimed for exclusive use, or false if it
+ * is available
+ * \sa acquire(), release()
+ */
+
+/**
* \brief Open a media device and retrieve device information
*
* Before populating the media graph or performing any operation that interact