libcamera: v4l2_videodevice: Pass FileDescriptor to open()

The V4L2VideoDevice::open() function that takes an open file handle
duplicates it internally, and leaves the original handle untouched. This
is documented but not enforced through language constructs. Fix it by
passing a FileDescriptor to the function.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

2 files changed, 10 insertions, 14 deletions

diff --git a/include/libcamera/internal/v4l2_videodevice.h b/include/libcamera/internal/v4l2_videodevice.h
index 80b66577..9f556f99 100644
--- a/include/libcamera/internal/v4l2_videodevice.h
+++ b/include/libcamera/internal/v4l2_videodevice.h
@@ -184,7 +184,7 @@ public:
 	~V4L2VideoDevice();
 
 	int open();
-	int open(int handle, enum v4l2_buf_type type);
+	int open(FileDescriptor handle, enum v4l2_buf_type type);
 	void close();
 
 	const char *driverName() const { return caps_.driver(); }
diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
index 3966483a..5f1cc6e2 100644
--- a/src/libcamera/v4l2_videodevice.cpp
+++ b/src/libcamera/v4l2_videodevice.cpp
@@ -612,16 +612,14 @@ int V4L2VideoDevice::open()
  * its type from the capabilities. This can be used to force a given device type
  * for memory-to-memory devices.
  *
- * The file descriptor \a handle is duplicated, and the caller is responsible
- * for closing the \a handle when it has no further use for it. The close()
- * function will close the duplicated file descriptor, leaving \a handle
- * untouched.
+ * The file descriptor \a handle is duplicated, no reference to the original
+ * handle is kept.
  *
  * \return 0 on success or a negative error code otherwise
  */
-int V4L2VideoDevice::open(int handle, enum v4l2_buf_type type)
+int V4L2VideoDevice::open(FileDescriptor handle, enum v4l2_buf_type type)
 {
-	UniqueFD newFd(dup(handle));
+	UniqueFD newFd = handle.dup();
 	if (!newFd.isValid()) {
 		LOG(V4L2, Error) << "Failed to duplicate file handle: "
 				 << strerror(errno);
@@ -1900,12 +1898,10 @@ int V4L2M2MDevice::open()
 
 	/*
 	 * The output and capture V4L2VideoDevice instances use the same file
-	 * handle for the same device node. The local file handle can be closed
-	 * as the V4L2VideoDevice::open() retains a handle by duplicating the
-	 * fd passed in.
+	 * handle for the same device node.
 	 */
-	UniqueFD fd(syscall(SYS_openat, AT_FDCWD, deviceNode_.c_str(),
-			    O_RDWR | O_NONBLOCK));
+	FileDescriptor fd(syscall(SYS_openat, AT_FDCWD, deviceNode_.c_str(),
+				  O_RDWR | O_NONBLOCK));
 	if (!fd.isValid()) {
 		ret = -errno;
 		LOG(V4L2, Error) << "Failed to open V4L2 M2M device: "
@@ -1913,11 +1909,11 @@ int V4L2M2MDevice::open()
 		return ret;
 	}
 
-	ret = output_->open(fd.get(), V4L2_BUF_TYPE_VIDEO_OUTPUT);
+	ret = output_->open(fd, V4L2_BUF_TYPE_VIDEO_OUTPUT);
 	if (ret)
 		goto err;
 
-	ret = capture_->open(fd.get(), V4L2_BUF_TYPE_VIDEO_CAPTURE);
+	ret = capture_->open(fd, V4L2_BUF_TYPE_VIDEO_CAPTURE);
 	if (ret)
 		goto err;