[media] v4l2-fh.rst: add cross references and markups

Add cross-references with the kernel-doc functions/structs
and improve the markups.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
This commit is contained in:
Mauro Carvalho Chehab 2016-07-22 09:31:16 -03:00
parent 378d4a54ae
commit 46f74f1d3e

View file

@ -1,27 +1,35 @@
V4L2 File handlers
------------------
struct v4l2_fh provides a way to easily keep file handle specific data
that is used by the V4L2 framework. New drivers must use struct v4l2_fh
since it is also used to implement priority handling (VIDIOC_G/S_PRIORITY).
struct :c:type:`v4l2_fh` provides a way to easily keep file handle specific
data that is used by the V4L2 framework.
The users of v4l2_fh (in the V4L2 framework, not the driver) know
whether a driver uses v4l2_fh as its file->private_data pointer by
testing the V4L2_FL_USES_V4L2_FH bit in video_device->flags. This bit is
set whenever v4l2_fh_init() is called.
.. attention::
New drivers must use struct :c:type:`v4l2_fh`
since it is also used to implement priority handling
(:ref:`VIDIOC_G_PRIORITY`).
struct 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
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 :cpp: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 v4l2_fh will be embedded in a larger structure.
In that case you should call v4l2_fh_init+v4l2_fh_add in open() and
v4l2_fh_del+v4l2_fh_exit in release().
In many cases the struct :c:type:`v4l2_fh` will be embedded in a larger
structure. In that case you should call:
#) :cpp:func:`v4l2_fh_init` and :cpp:func:`v4l2_fh_add` in ``open()``
#) :cpp:func:`v4l2_fh_del` and :cpp:func:`v4l2_fh_exit` in ``release()``
Drivers can extract their own file handle structure by using the container_of
macro. Example:
macro.
.. code-block:: none
Example:
.. code-block:: c
struct my_fh {
int blah;
@ -63,73 +71,66 @@ macro. Example:
return 0;
}
Below is a short description of the v4l2_fh functions used:
Below is a short description of the :c:type:`v4l2_fh` functions used:
.. code-block:: none
:cpp:func:`v4l2_fh_init <v4l2_fh_init>`
(:c:type:`fh <v4l2_fh>`, :c:type:`vdev <video_device>`)
void v4l2_fh_init(struct v4l2_fh *fh, struct video_device *vdev)
Initialise the file handle. This *MUST* be performed in the driver's
v4l2_file_operations->open() handler.
- Initialise the file handle. This **MUST** be performed in the driver's
:c:type:`v4l2_file_operations`->open() handler.
.. code-block:: none
void v4l2_fh_add(struct v4l2_fh *fh)
:cpp:func:`v4l2_fh_add <v4l2_fh_add>`
(:c:type:`fh <v4l2_fh>`)
Add a v4l2_fh to video_device file handle list. Must be called once the
file handle is completely initialized.
- Add a :c:type:`v4l2_fh` to :c:type:`video_device` file handle list.
Must be called once the file handle is completely initialized.
.. code-block:: none
:cpp:func:`v4l2_fh_del <v4l2_fh_del>`
(:c:type:`fh <v4l2_fh>`)
void v4l2_fh_del(struct v4l2_fh *fh)
Unassociate the file handle from video_device(). The file handle
- Unassociate the file handle from :c:type:`video_device`. The file handle
exit function may now be called.
.. code-block:: none
:cpp:func:`v4l2_fh_exit <v4l2_fh_exit>`
(:c:type:`fh <v4l2_fh>`)
void v4l2_fh_exit(struct v4l2_fh *fh)
Uninitialise the file handle. After uninitialisation the v4l2_fh
- Uninitialise the file handle. After uninitialisation the :c:type:`v4l2_fh`
memory can be freed.
If struct v4l2_fh is not embedded, then you can use these helper functions:
If struct :c:type:`v4l2_fh` is not embedded, then you can use these helper functions:
.. code-block:: none
:cpp:func:`v4l2_fh_open <v4l2_fh_open>`
(struct file \*filp)
int 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.
This allocates a struct v4l2_fh, initializes it and adds it to the struct
video_device associated with the file struct.
:cpp:func:`v4l2_fh_release <v4l2_fh_release>`
(struct file \*filp)
.. code-block:: none
int v4l2_fh_release(struct file *filp)
This deletes it from the struct video_device associated with the file
struct, uninitialised the v4l2_fh and frees it.
These two functions can be plugged into the v4l2_file_operation's open() and
release() ops.
- 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 v4l2_fh struct is the only open filehandle of the associated
device node:
whether the :c:type:`v4l2_fh` struct is the only open filehandle of the
associated device node:
.. code-block:: none
:cpp:func:`v4l2_fh_is_singular <v4l2_fh_is_singular>`
(:c:type:`fh <v4l2_fh>`)
int v4l2_fh_is_singular(struct v4l2_fh *fh)
- Returns 1 if the file handle is the only open file handle, else 0.
Returns 1 if the file handle is the only open file handle, else 0.
:cpp:func:`v4l2_fh_is_singular_file <v4l2_fh_is_singular_file>`
(struct file \*filp)
.. code-block:: none
int v4l2_fh_is_singular_file(struct file *filp)
Same, but it calls v4l2_fh_is_singular with filp->private_data.
- Same, but it calls v4l2_fh_is_singular with filp->private_data.
V4L2 File Handler kAPI