blob: 9e87d5ca3e4ae80d47bd75eb1a249fb62d5e4cdb (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
|
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 :cpp:func:`v4l2_fh_add` in ``open()``
#) :c: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:
.. 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
|
