[libcamera-devel] [PATCH v8 3/9] 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: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>
---
* Changes since v7
- Expand comment
- Update error message

* Changes since v6
- Use sysfs:: helper.
- Do not try to return std::string { nullptr } on error.

* Changes since v5
- Expand documentation
- Use DeviceEnumerator interface to lookup device path
- Include stdlib.h
- Use realpath(..., nullptr); ...; free();

* Changes since v3
- s/the device path/the device path in sysfs/
---
 include/libcamera/internal/v4l2_device.h |  1 +
 src/libcamera/v4l2_device.cpp            | 31 ++++++++++++++++++++++++
 2 files changed, 32 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..65830d41f3cb6e9d 100644
--- a/src/libcamera/v4l2_device.cpp
+++ b/src/libcamera/v4l2_device.cpp
@@ -9,12 +9,15 @@
 
 #include <fcntl.h>
 #include <iomanip>
+#include <limits.h>
+#include <stdlib.h>
 #include <string.h>
 #include <sys/ioctl.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 
 #include "libcamera/internal/log.h"
+#include "libcamera/internal/sysfs.h"
 #include "libcamera/internal/utils.h"
 #include "libcamera/internal/v4l2_controls.h"
 
@@ -350,6 +353,34 @@ int V4L2Device::setControls(ControlList *ctrls)
 	return ret;
 }
 
+/**
+ * \brief Retrieve the device path in sysfs
+ *
+ * This function returns the sysfs path to the physical device backing the V4L2
+ * device. The path is guaranteed to be an absolute path, without any symbolic
+ * link.
+ *
+ * It includes the sysfs mount point prefix
+ *
+ * \return The device path in sysfs
+ */
+std::string V4L2Device::devicePath() const
+{
+	std::string devicePath = sysfs::charDevPath(deviceNode_) + "/device";
+
+	char *realPath = realpath(devicePath.c_str(), nullptr);
+	if (!realPath) {
+		LOG(V4L2, Fatal)
+			<< "Can not resolve device path for " << devicePath;
+		return {};
+	}
+
+	std::string path{ realPath };
+	free(realPath);
+
+	return path;
+}
+
 /**
  * \brief Perform an IOCTL system call on the device node
  * \param[in] request The IOCTL request code
-- 
2.28.0