142 строки
3.8 KiB
ReStructuredText
142 строки
3.8 KiB
ReStructuredText
.. 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
|