libcamera: Add V4L2 Device object

Provide a helper V4L2 device object capable of interacting with the
V4L2 Linux Kernel APIs.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/include/v4l2_device.h

@@ -0,0 +1,60 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * v4l2_device.h - V4L2 Device
+ */
+#ifndef __LIBCAMERA_V4L2_DEVICE_H__
+#define __LIBCAMERA_V4L2_DEVICE_H__
+
+#include <string>
+
+#include <linux/videodev2.h>
+
+namespace libcamera {
+
+struct V4L2Capability final : v4l2_capability {
+	const char *driver() const
+	{
+		return reinterpret_cast<const char *>(v4l2_capability::driver);
+	}
+	const char *card() const
+	{
+		return reinterpret_cast<const char *>(v4l2_capability::card);
+	}
+	const char *bus_info() const
+	{
+		return reinterpret_cast<const char *>(v4l2_capability::bus_info);
+	}
+
+	bool isCapture() const { return capabilities & V4L2_CAP_VIDEO_CAPTURE; }
+	bool isOutput() const { return capabilities & V4L2_CAP_VIDEO_OUTPUT; }
+	bool hasStreaming() const { return capabilities & V4L2_CAP_STREAMING; }
+};
+
+class V4L2Device
+{
+public:
+	V4L2Device(const std::string &devnode);
+	V4L2Device(const V4L2Device &) = delete;
+	~V4L2Device();
+
+	void operator=(const V4L2Device &) = delete;
+
+	int open();
+	bool isOpen() const;
+	void close();
+
+	const char *driverName() const { return caps_.driver(); }
+	const char *deviceName() const { return caps_.card(); }
+	const char *busName() const { return caps_.bus_info(); }
+
+private:
+	std::string devnode_;
+	int fd_;
+	V4L2Capability caps_;
+};
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_V4L2_DEVICE_H__ */

src/libcamera/meson.build

@@ -11,6 +11,7 @@ libcamera_sources = files([
     'pipeline_handler.cpp',
     'signal.cpp',
     'timer.cpp',
+    'v4l2_device.cpp',
 ])
 
 libcamera_headers = files([
@@ -21,6 +22,7 @@ libcamera_headers = files([
     'include/media_object.h',
     'include/pipeline_handler.h',
     'include/utils.h',
+    'include/v4l2_device.h',
 ])
 
 libcamera_internal_includes =  include_directories('include')

src/libcamera/v4l2_device.cpp

@@ -0,0 +1,186 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * v4l2_device.cpp - V4L2 Device
+ */
+
+#include <fcntl.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "log.h"
+#include "v4l2_device.h"
+
+/**
+ * \file v4l2_device.h
+ * \brief V4L2 Device API
+ */
+namespace libcamera {
+
+/**
+ * \struct V4L2Capability
+ * \brief struct v4l2_capability object wrapper and helpers
+ *
+ * The V4L2Capability structure manages the information returned by the
+ * VIDIOC_QUERYCAP ioctl.
+ */
+
+/**
+ * \fn const char *V4L2Capability::driver()
+ * \brief Retrieve the driver module name
+ * \return The string containing the name of the driver module
+ */
+
+/**
+ * \fn const char *V4L2Capability::card()
+ * \brief Retrieve the device card name
+ * \return The string containing the device name
+ */
+
+/**
+ * \fn const char *V4L2Capability::bus_info()
+ * \brief Retrieve the location of the device in the system
+ * \return The string containing the device location
+ */
+
+/**
+ * \fn bool V4L2Capability::isCapture()
+ * \brief Identify if the device is capable of capturing video
+ * \return True if the device can capture video frames
+ */
+
+/**
+ * \fn bool V4L2Capability::isOutput()
+ * \brief Identify if the device is capable of outputting video
+ * \return True if the device can output video frames
+ */
+
+/**
+ * \fn bool V4L2Capability::hasStreaming()
+ * \brief Determine if the device can perform Streaming I/O
+ * \return True if the device provides Streaming I/O IOCTLs
+ */
+
+/**
+ * \class V4L2Device
+ * \brief V4L2Device object and API
+ *
+ * The V4L2 Device API class models an instance of a V4L2 device node.
+ * It is constructed with the path to a V4L2 video device node. The device node
+ * is only opened upon a call to open() which must be checked for success.
+ *
+ * The device capabilities are validated when the device is opened and the
+ * device is rejected if it is not a suitable V4L2 capture or output device, or
+ * if the device does not support streaming I/O.
+ *
+ * No API call other than open(), isOpen() and close() shall be called on an
+ * unopened device instance.
+ *
+ * Upon destruction any device left open will be closed, and any resources
+ * released.
+ */
+
+/**
+ * \brief Construct a V4L2Device
+ * \param devnode The file-system path to the video device node
+ */
+V4L2Device::V4L2Device(const std::string &devnode)
+	: devnode_(devnode), fd_(-1)
+{
+}
+
+V4L2Device::~V4L2Device()
+{
+	close();
+}
+
+/**
+ * \brief Open a V4L2 device and query its capabilities
+ * \return 0 on success, or a negative error code otherwise
+ */
+int V4L2Device::open()
+{
+	int ret;
+
+	if (isOpen()) {
+		LOG(Error) << "Device already open";
+		return -EBUSY;
+	}
+
+	ret = ::open(devnode_.c_str(), O_RDWR);
+	if (ret < 0) {
+		ret = -errno;
+		LOG(Error) << "Failed to open V4L2 device '" << devnode_
+			   << "': " << strerror(-ret);
+		return ret;
+	}
+	fd_ = ret;
+
+	ret = ioctl(fd_, VIDIOC_QUERYCAP, &caps_);
+	if (ret < 0) {
+		ret = -errno;
+		LOG(Error) << "Failed to query device capabilities: "
+			   << strerror(-ret);
+		return ret;
+	}
+
+	LOG(Debug) << "Opened '" << devnode_ << "' "
+		   << caps_.bus_info() << ": " << caps_.driver()
+		   << ": " << caps_.card();
+
+	if (!caps_.isCapture() && !caps_.isOutput()) {
+		LOG(Debug) << "Device is not a supported type";
+		return -EINVAL;
+	}
+
+	if (!caps_.hasStreaming()) {
+		LOG(Error) << "Device does not support streaming I/O";
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/**
+ * \brief Check if device is successfully opened
+ * \return True if the device is open, false otherwise
+ */
+bool V4L2Device::isOpen() const
+{
+	return fd_ != -1;
+}
+
+/**
+ * \brief Close the device, releasing any resources acquired by open()
+ */
+void V4L2Device::close()
+{
+	if (fd_ < 0)
+		return;
+
+	::close(fd_);
+	fd_ = -1;
+}
+
+/**
+ * \fn const char *V4L2Device::driverName()
+ * \brief Retrieve the name of the V4L2 device driver
+ * \return The string containing the driver name
+ */
+
+/**
+ * \fn const char *V4L2Device::deviceName()
+ * \brief Retrieve the name of the V4L2 device
+ * \return The string containing the device name
+ */
+
+/**
+ * \fn const char *V4L2Device::busName()
+ * \brief Retrieve the location of the device in the system
+ * \return The string containing the device location
+ */
+
+} /* namespace libcamera */