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| -rw-r--r-- | Documentation/video4linux/v4l2-framework.txt | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/Documentation/video4linux/v4l2-framework.txt b/Documentation/video4linux/v4l2-framework.txt index 5b9205a..48f0adf 100644 --- a/Documentation/video4linux/v4l2-framework.txt +++ b/Documentation/video4linux/v4l2-framework.txt @@ -608,3 +608,75 @@ scatter/gather method (videobuf-dma-sg), DMA with linear access Please see Documentation/video4linux/videobuf for more information on how to use the videobuf layer. + +struct v4l2_fh +-------------- + +struct v4l2_fh provides a way to easily keep file handle specific data +that is used by the V4L2 framework. Using v4l2_fh is optional for +drivers. + +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. + +Useful functions: + +- v4l2_fh_init() + + Initialise the file handle. This *MUST* be performed in the driver's + v4l2_file_operations->open() handler. + +- v4l2_fh_add() + + Add a v4l2_fh to video_device file handle list. May be called after + initialising the file handle. + +- v4l2_fh_del() + + Unassociate the file handle from video_device(). The file handle + exit function may now be called. + +- v4l2_fh_exit() + + Uninitialise the file handle. After uninitialisation the v4l2_fh + memory can be freed. + +struct v4l2_fh is allocated as a part of the driver's own file handle +structure and is set to file->private_data in the driver's open +function by the driver. Drivers can extract their own file handle +structure by using the container_of macro. Example: + +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; + + ... + + ret = v4l2_fh_init(&my_fh->fh, vfd); + if (ret) + return ret; + + v4l2_fh_add(&my_fh->fh); + + file->private_data = &my_fh->fh; + + ... +} + +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); + + ... +} |