[libcamera-devel] [PATCH v4 1/5] libcamera: v4l2_device: Add method to lookup device path

[Niklas Söderlund]

Add a method to lookup a V4L2 devices path in sysfs.

Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>
---
* Changes since v3
- s/the device path/the device path in sysfs/
---
 include/libcamera/internal/v4l2_device.h |  1 +
 src/libcamera/v4l2_device.cpp            | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/libcamera/internal/v4l2_device.h b/include/libcamera/internal/v4l2_device.h
index bf643f2ec966bb33..3b605aab343b3b94 100644
--- a/include/libcamera/internal/v4l2_device.h
+++ b/include/libcamera/internal/v4l2_device.h
@@ -30,6 +30,7 @@ public:
 	int setControls(ControlList *ctrls);
 
 	const std::string &deviceNode() const { return deviceNode_; }
+	std::string devicePath() const;
 
 protected:
 	V4L2Device(const std::string &deviceNode);
diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
index 56ea1ddda2c1425f..1cb8181ab6fd5a8d 100644
--- a/src/libcamera/v4l2_device.cpp
+++ b/src/libcamera/v4l2_device.cpp
@@ -9,6 +9,7 @@
 
 #include <fcntl.h>
 #include <iomanip>
+#include <limits.h>
 #include <string.h>
 #include <sys/ioctl.h>
 #include <sys/syscall.h>
@@ -350,6 +351,29 @@ int V4L2Device::setControls(ControlList *ctrls)
 	return ret;
 }
 
+/**
+ * \brief Retrieve the device path in sysfs
+ *
+ * The device path in sysfs describes the device backing the V4L2 device.
+ *
+ * \todo When switching to C++17 use std::filesystem:: in the implementation.
+ * \todo Query udev for this information as the path created for vdev here
+ * migh not be correct.
+ *
+ * \return The device path in sysfs
+ */
+std::string V4L2Device::devicePath() const
+{
+	std::string vdev = basename(deviceNode_.c_str());
+	std::string sysfs = "/sys/class/video4linux/" + vdev + "/device";
+
+	char path[PATH_MAX];
+	if (!realpath(sysfs.c_str(), path))
+		LOG(V4L2, Fatal) << "Can not resolve path for " << deviceNode_;
+
+	return path;
+}
+
 /**
  * \brief Perform an IOCTL system call on the device node
  * \param[in] request The IOCTL request code
-- 
2.27.0