libcamera: Introduce V4L2Device base class

The V4L2 devices and subdevices share a few common operations,like
opening and closing a device node, and perform IOCTLs on the device.

With the forthcoming introduction of support for V4L2 controls, the
quantity of shared code will increase, as the control support
implementation is identical for the two derived classes.

To maximize code re-use and avoid duplications, provide a V4L2Device
base class which groups the common operations and members.

The newly introduced base class provides methods to open/close a device
node, access the file descriptor, and perform IOCTLs on the device.

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

1 files changed, 140 insertions, 0 deletions

diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
new file mode 100644
index 00000000..99621a72
--- /dev/null
+++ b/src/libcamera/v4l2_device.cpp
@@ -0,0 +1,140 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * v4l2_device.cpp - Common base for V4L2 video devices and subdevices
+ */
+
+#include "v4l2_device.h"
+
+#include <fcntl.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#include "log.h"
+
+/**
+ * \file v4l2_device.h
+ * \brief Common base for V4L2 devices and subdevices
+ */
+
+namespace libcamera {
+
+LOG_DEFINE_CATEGORY(V4L2)
+
+/**
+ * \class V4L2Device
+ * \brief Base class for V4L2VideoDevice and V4L2Subdevice
+ *
+ * The V4L2Device class groups together the methods and fields common to
+ * both the V4L2VideoDevice and V4L2Subdevice classes, and provides a base
+ * class whith methods to open and close the device node associated with the
+ * device and to perform IOCTL system calls on it.
+ *
+ * The V4L2Device class cannot be instantiated directly, as its constructor
+ * is protected. Users should instead create instances of one the derived
+ * classes to model either a V4L2 video device or a V4L2 subdevice.
+ */
+
+/**
+ * \brief Construct a V4L2Device
+ * \param[in] deviceNode The device node filesystem path
+ *
+ * Initialize the file descriptor to -1 and store the \a deviceNode to be used
+ * at open() time, and the \a logTag to prefix log messages with.
+ */
+V4L2Device::V4L2Device(const std::string &deviceNode)
+	: deviceNode_(deviceNode), fd_(-1)
+{
+}
+
+/**
+ * \brief Destroy a V4L2Device
+ */
+V4L2Device::~V4L2Device()
+{
+}
+
+/**
+ * \brief Open a V4L2 device node
+ * \param[in] flags Access mode flags
+ *
+ * Open the device node path with the provided access mode \a flags and
+ * initialize the file descriptor, which was initially set to -1.
+ *
+ * \return 0 on success or a negative error code otherwise
+ */
+int V4L2Device::open(unsigned int flags)
+{
+	if (isOpen()) {
+		LOG(V4L2, Error) << "Device already open";
+		return -EBUSY;
+	}
+
+	int ret = ::open(deviceNode_.c_str(), flags);
+	if (ret < 0) {
+		ret = -errno;
+		LOG(V4L2, Error) << "Failed to open V4L2 device: "
+				 << strerror(-ret);
+		return ret;
+	}
+
+	fd_ = ret;
+
+	return 0;
+}
+
+/**
+ * \brief Close the device node
+ *
+ * Reset the file descriptor to -1
+ */
+void V4L2Device::close()
+{
+	if (!isOpen())
+		return;
+
+	if (::close(fd_) < 0)
+		LOG(V4L2, Error) << "Failed to close V4L2 device: "
+				 << strerror(errno);
+	fd_ = -1;
+}
+
+/**
+ * \fn V4L2Device::isOpen()
+ * \brief Check if the V4L2 device node is open
+ * \return True if the V4L2 device node is open, false otherwise
+ */
+
+/**
+ * \brief Perform an IOCTL system call on the device node
+ * \param[in] request The IOCTL request code
+ * \param[in] argp A pointer to the IOCTL argument
+ * \return 0 on success or a negative error code otherwise
+ */
+int V4L2Device::ioctl(unsigned long request, void *argp)
+{
+	/*
+	 * Printing out an error message is usually better performed
+	 * in the caller, which can provide more context.
+	 */
+	if (::ioctl(fd_, request, argp) < 0)
+		return -errno;
+
+	return 0;
+}
+
+/**
+ * \fn V4L2Device::deviceNode()
+ * \brief Retrieve the device node path
+ * \return The device node path
+ */
+
+/**
+ * \fn V4L2Device::fd()
+ * \brief Retrieve the V4L2 device file descriptor
+ * \return The V4L2 device file descriptor, -1 if the device node is not open
+ */
+
+} /* namespace libcamera */