From 378d4a54aec014b8d2e8ed2ac6bb985e7371c098 Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Fri, 22 Jul 2016 09:10:20 -0300 Subject: [PATCH] [media] v4l2-fh.rst: add fh contents from v4l2-framework.rst Move the v4l2_fh specific content from v4l2-framework.rst to v4l2-fh.rst. Signed-off-by: Mauro Carvalho Chehab --- Documentation/media/kapi/v4l2-fh.rst | 134 ++++++++++++++++++++ Documentation/media/kapi/v4l2-framework.rst | 133 ------------------- 2 files changed, 134 insertions(+), 133 deletions(-) diff --git a/Documentation/media/kapi/v4l2-fh.rst b/Documentation/media/kapi/v4l2-fh.rst index 9309c18e967a..f39374262d3f 100644 --- a/Documentation/media/kapi/v4l2-fh.rst +++ b/Documentation/media/kapi/v4l2-fh.rst @@ -1,3 +1,137 @@ +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). + +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. + +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 +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(). + +Drivers can extract their own file handle structure by using the container_of +macro. Example: + +.. code-block:: none + + 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 v4l2_fh functions used: + +.. code-block:: none + + 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. + +.. code-block:: none + + void v4l2_fh_add(struct v4l2_fh *fh) + + Add a v4l2_fh to video_device file handle list. Must be called once the + file handle is completely initialized. + +.. code-block:: none + + void v4l2_fh_del(struct v4l2_fh *fh) + + Unassociate the file handle from video_device(). The file handle + exit function may now be called. + +.. code-block:: none + + void v4l2_fh_exit(struct v4l2_fh *fh) + + Uninitialise the file handle. After uninitialisation the v4l2_fh + memory can be freed. + + +If struct v4l2_fh is not embedded, then you can use these helper functions: + +.. code-block:: none + + int v4l2_fh_open(struct file *filp) + + This allocates a struct v4l2_fh, initializes it and adds it to the struct + video_device associated with the file struct. + +.. 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. + + +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: + +.. code-block:: none + + int v4l2_fh_is_singular(struct v4l2_fh *fh) + + Returns 1 if the file handle is the only open file handle, else 0. + +.. code-block:: none + + int v4l2_fh_is_singular_file(struct file *filp) + + Same, but it calls v4l2_fh_is_singular with filp->private_data. + + V4L2 File Handler kAPI ^^^^^^^^^^^^^^^^^^^^^^ .. kernel-doc:: include/media/v4l2-fh.h diff --git a/Documentation/media/kapi/v4l2-framework.rst b/Documentation/media/kapi/v4l2-framework.rst index d46380ac7c1d..8b4f684e1a7a 100644 --- a/Documentation/media/kapi/v4l2-framework.rst +++ b/Documentation/media/kapi/v4l2-framework.rst @@ -80,139 +80,6 @@ The V4L2 framework also optionally integrates with the media framework. If a driver sets the struct v4l2_device mdev field, sub-devices and video nodes will automatically appear in the media framework as entities. -struct v4l2_fh --------------- - -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). - -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. - -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 -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(). - -Drivers can extract their own file handle structure by using the container_of -macro. Example: - -.. code-block:: none - - 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 v4l2_fh functions used: - -.. code-block:: none - - 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. - -.. code-block:: none - - void v4l2_fh_add(struct v4l2_fh *fh) - - Add a v4l2_fh to video_device file handle list. Must be called once the - file handle is completely initialized. - -.. code-block:: none - - void v4l2_fh_del(struct v4l2_fh *fh) - - Unassociate the file handle from video_device(). The file handle - exit function may now be called. - -.. code-block:: none - - void v4l2_fh_exit(struct v4l2_fh *fh) - - Uninitialise the file handle. After uninitialisation the v4l2_fh - memory can be freed. - - -If struct v4l2_fh is not embedded, then you can use these helper functions: - -.. code-block:: none - - int v4l2_fh_open(struct file *filp) - - This allocates a struct v4l2_fh, initializes it and adds it to the struct - video_device associated with the file struct. - -.. 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. - - -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: - -.. code-block:: none - - int v4l2_fh_is_singular(struct v4l2_fh *fh) - - Returns 1 if the file handle is the only open file handle, else 0. - -.. code-block:: none - - int v4l2_fh_is_singular_file(struct file *filp) - - Same, but it calls v4l2_fh_is_singular with filp->private_data. - V4L2 clocks ----------- -- 2.20.1