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authorMauro Carvalho Chehab <mchehab+huawei@kernel.org>2020-03-04 10:50:14 +0100
committerMauro Carvalho Chehab <mchehab+huawei@kernel.org>2020-04-14 10:32:45 +0200
commitff768f596fa19e719c88fbc9bd65e13145d944e7 (patch)
tree8574b980ade74110380566b7f07f84710db37fcd /Documentation/media/kapi/v4l2-fh.rst
parentmedia: docs: move uAPI book to userspace-api/media (diff)
downloadwireguard-linux-ff768f596fa19e719c88fbc9bd65e13145d944e7.tar.xz
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media: docs: kAPI docs: move them to driver-api
All those documents describe the media driver API. So, move them to the right place within the Kernel documentation. Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
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-.. SPDX-License-Identifier: GPL-2.0
-
-V4L2 File handlers
-------------------
-
-struct :c:type:`v4l2_fh` provides a way to easily keep file handle specific
-data that is used by the V4L2 framework.
-
-.. attention::
- New drivers must use struct :c:type:`v4l2_fh`
- since it is also used to implement priority handling
- (:ref:`VIDIOC_G_PRIORITY`).
-
-The users of :c:type:`v4l2_fh` (in the V4L2 framework, not the driver) know
-whether a driver uses :c:type:`v4l2_fh` as its ``file->private_data`` pointer
-by testing the ``V4L2_FL_USES_V4L2_FH`` bit in :c:type:`video_device`->flags.
-This bit is set whenever :c:func:`v4l2_fh_init` is called.
-
-struct :c:type:`v4l2_fh` is allocated as a part of the driver's own file handle
-structure and ``file->private_data`` is set to it in the driver's ``open()``
-function by the driver.
-
-In many cases the struct :c:type:`v4l2_fh` will be embedded in a larger
-structure. In that case you should call:
-
-#) :c:func:`v4l2_fh_init` and :c:func:`v4l2_fh_add` in ``open()``
-#) :c:func:`v4l2_fh_del` and :c:func:`v4l2_fh_exit` in ``release()``
-
-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);
-
- ...
-
- file->private_data = &my_fh->fh;
- v4l2_fh_add(&my_fh->fh);
- return 0;
- }
-
- int my_release(struct file *file)
- {
- struct v4l2_fh *fh = file->private_data;
- struct my_fh *my_fh = container_of(fh, struct my_fh, fh);
-
- ...
- v4l2_fh_del(&my_fh->fh);
- 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>`)
-
-- 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>`)
-
-- 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.
-
-
-If struct :c:type:`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 :c:type:`v4l2_fh`, initializes it and adds it to
- the struct :c:type:`video_device` associated with the file struct.
-
-:c:func:`v4l2_fh_release <v4l2_fh_release>`
-(struct file \*filp)
-
-- This deletes it from the struct :c:type:`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