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+.. SPDX-License-Identifier: GPL-2.0
+
+V4L2 File handles
+-----------------
+
+struct v4l2_fh provides a way to easily keep file handle specific data that is
+used by the V4L2 framework. Its usage is mandatory in all drivers.
+
+struct v4l2_fh is allocated in the driver's ``open()`` file operation handler.
+It is typically embedded in a larger driver-specific structure. The
+:c:type:`v4l2_fh` must be initialized with a call to :c:func:`v4l2_fh_init`,
+and added to the video device with :c:func:`v4l2_fh_add`. This associates the
+:c:type:`v4l2_fh` with the :c:type:`file` by setting ``file->private_data`` to
+point to the :c:type:`v4l2_fh`.
+
+Similarly, the struct v4l2_fh is freed in the driver's ``release()`` file
+operation handler. It must be removed from the video device with
+:c:func:`v4l2_fh_del` and cleaned up with :c:func:`v4l2_fh_exit` before being
+freed.
+
+Drivers must not access ``file->private_data`` directly. They can retrieve the
+:c:type:`v4l2_fh` associated with a :c:type:`file` by calling
+:c:func:`file_to_v4l2_fh`. Drivers can extract their own file handle structure
+by using the container_of macro.
+
+Example:
+
+.. code-block:: c
+
+	struct my_fh {
+		int blah;
+		struct v4l2_fh fh;
+	};
+
+	...
+
+	int my_open(struct file *file)
+	{
+		struct my_fh *my_fh;
+		struct video_device *vfd;
+		int ret;
+
+		...
+
+		my_fh = kzalloc(sizeof(*my_fh), GFP_KERNEL);
+
+		...
+
+		v4l2_fh_init(&my_fh->fh, vfd);
+
+		...
+
+		v4l2_fh_add(&my_fh->fh, file);
+		return 0;
+	}
+
+	int my_release(struct file *file)
+	{
+		struct v4l2_fh *fh = file_to_v4l2_fh(file);
+		struct my_fh *my_fh = container_of(fh, struct my_fh, fh);
+
+		...
+		v4l2_fh_del(&my_fh->fh, file);
+		v4l2_fh_exit(&my_fh->fh);
+		kfree(my_fh);
+		return 0;
+	}
+
+Below is a short description of the :c:type:`v4l2_fh` functions used:
+
+:c:func:`v4l2_fh_init <v4l2_fh_init>`
+(:c:type:`fh <v4l2_fh>`, :c:type:`vdev <video_device>`)
+
+- Initialise the file handle. This **MUST** be performed in the driver's
+  :c:type:`v4l2_file_operations`->open() handler.
+
+:c:func:`v4l2_fh_add <v4l2_fh_add>`
+(:c:type:`fh <v4l2_fh>`, struct file \*filp)
+
+- Add a :c:type:`v4l2_fh` to :c:type:`video_device` file handle list.
+  Must be called once the file handle is completely initialized.
+
+:c:func:`v4l2_fh_del <v4l2_fh_del>`
+(:c:type:`fh <v4l2_fh>`, struct file \*filp)
+
+- Unassociate the file handle from :c:type:`video_device`. The file handle
+  exit function may now be called.
+
+:c:func:`v4l2_fh_exit <v4l2_fh_exit>`
+(:c:type:`fh <v4l2_fh>`)
+
+- Uninitialise the file handle. After uninitialisation the :c:type:`v4l2_fh`
+  memory can be freed.
+
+:c:func:`file_to_v4l2_fh <file_to_v4l2_fh>`
+(struct file \*filp)
+
+- Retrieve the :c:type:`v4l2_fh` instance associated with a :c:type:`file`.
+
+If struct v4l2_fh is not embedded, then you can use these helper functions:
+
+:c:func:`v4l2_fh_open <v4l2_fh_open>`
+(struct file \*filp)
+
+- This allocates a struct v4l2_fh, initializes it and adds it to
+  the struct video_device associated with the file struct.
+
+:c:func:`v4l2_fh_release <v4l2_fh_release>`
+(struct file \*filp)
+
+- This deletes it from the struct video_device associated with the
+  file struct, uninitialised the :c:type:`v4l2_fh` and frees it.
+
+These two functions can be plugged into the v4l2_file_operation's ``open()``
+and ``release()`` ops.
+
+Several drivers need to do something when the first file handle is opened and
+when the last file handle closes. Two helper functions were added to check
+whether the :c:type:`v4l2_fh` struct is the only open filehandle of the
+associated device node:
+
+:c:func:`v4l2_fh_is_singular <v4l2_fh_is_singular>`
+(:c:type:`fh <v4l2_fh>`)
+
+-  Returns 1 if the file handle is the only open file handle, else 0.
+
+:c:func:`v4l2_fh_is_singular_file <v4l2_fh_is_singular_file>`
+(struct file \*filp)
+
+- Same, but it calls v4l2_fh_is_singular with filp->private_data.
+
+
+V4L2 fh functions and data structures
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. kernel-doc:: include/media/v4l2-fh.h