Message-ID: <e3250369-1a68-d061-3618-fd285f760315@collabora.com>
Date:   Mon, 3 Jul 2023 13:17:10 +0200
From:   Benjamin Gaignard <benjamin.gaignard@...labora.com>
To:     Hsia-Jun Li <Randy.Li@...aptics.com>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        p.zabel@...gutronix.de, ming.qian@....com,
        hverkuil-cisco@...all.nl, gregkh@...uxfoundation.org,
        ezequiel@...guardiasur.com.ar,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, nicolas.dufresne@...labora.com,
        linux-staging@...ts.linux.dev, kernel@...labora.com,
        mchehab@...nel.org, tfiga@...omium.org, m.szyprowski@...sung.com,
        ayaka <ayaka@...lik.info>
Subject: Re: [PATCH v3 10/11] media: v4l2: Add DELETE_BUF ioctl


Le 03/07/2023 à 13:02, Hsia-Jun Li a écrit :
>
>
> On 7/3/23 18:35, Benjamin Gaignard wrote:
>> CAUTION: Email originated externally, do not click links or open 
>> attachments unless you recognize the sender and know the content is 
>> safe.
>>
>>
>> Le 03/07/2023 à 11:20, Hsia-Jun Li a écrit :
>>>
>>> On 7/3/23 16:52, Benjamin Gaignard wrote:
>>>> CAUTION: Email originated externally, do not click links or open
>>>> attachments unless you recognize the sender and know the content is
>>>> safe.
>>>>
>>>>
>>>> Le 03/07/2023 à 10:19, Hsia-Jun Li a écrit :
>>>>>
>>>>> On 7/3/23 16:12, Benjamin Gaignard wrote:
>>>>>> CAUTION: Email originated externally, do not click links or open
>>>>>> attachments unless you recognize the sender and know the content is
>>>>>> safe.
>>>>>>
>>>>>>
>>>>>> Le 30/06/2023 à 11:43, Hsia-Jun Li a écrit :
>>>>>>>
>>>>>>> On 6/27/23 16:47, Hsia-Jun Li wrote:
>>>>>>>> CAUTION: Email originated externally, do not click links or open
>>>>>>>> attachments unless you recognize the sender and know the 
>>>>>>>> content is
>>>>>>>> safe.
>>>>>>>>
>>>>>>>>
>>>>>>>> On 6/27/23 16:43, Benjamin Gaignard wrote:
>>>>>>>>> CAUTION: Email originated externally, do not click links or open
>>>>>>>>> attachments unless you recognize the sender and know the 
>>>>>>>>> content is
>>>>>>>>> safe.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Le 27/06/2023 à 09:30, Hsia-Jun Li a écrit :
>>>>>>>>>>
>>>>>>>>>> On 6/22/23 21:13, Benjamin Gaignard wrote:
>>>>>>>>>>> CAUTION: Email originated externally, do not click links or 
>>>>>>>>>>> open
>>>>>>>>>>> attachments unless you recognize the sender and know the
>>>>>>>>>>> content is
>>>>>>>>>>> safe.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> VIDIOC_DELETE_BUF ioctl allows to delete a buffer from a queue.
>>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Benjamin Gaignard
>>>>>>>>>>> <benjamin.gaignard@...labora.com>
>>>>>>>>>>> ---
>>>>>>>>>>> .../userspace-api/media/v4l/user-func.rst | 1 +
>>>>>>>>>>> .../media/v4l/vidioc-delete-buf.rst | 51
>>>>>>>>>>> +++++++++++++++++++
>>>>>>>>>>> .../media/common/videobuf2/videobuf2-core.c | 33 ++++++++++++
>>>>>>>>>>> .../media/common/videobuf2/videobuf2-v4l2.c | 6 +++
>>>>>>>>>>> drivers/media/v4l2-core/v4l2-dev.c | 1 +
>>>>>>>>>>> drivers/media/v4l2-core/v4l2-ioctl.c | 10 ++++
>>>>>>>>>>> include/media/v4l2-ioctl.h | 4 ++
>>>>>>>>>>> include/media/videobuf2-core.h | 9 ++++
>>>>>>>>>>> include/media/videobuf2-v4l2.h | 11 ++++
>>>>>>>>>>> include/uapi/linux/videodev2.h | 2 +
>>>>>>>>>>>   10 files changed, 128 insertions(+)
>>>>>>>>>>>   create mode 100644
>>>>>>>>>>> Documentation/userspace-api/media/v4l/vidioc-delete-buf.rst
>>>>>>>>>>>
>>>>>>>>>>> diff --git 
>>>>>>>>>>> a/Documentation/userspace-api/media/v4l/user-func.rst
>>>>>>>>>>> b/Documentation/userspace-api/media/v4l/user-func.rst
>>>>>>>>>>> index 15ff0bf7bbe6..8c74016e12fd 100644
>>>>>>>>>>> --- a/Documentation/userspace-api/media/v4l/user-func.rst
>>>>>>>>>>> +++ b/Documentation/userspace-api/media/v4l/user-func.rst
>>>>>>>>>>> @@ -17,6 +17,7 @@ Function Reference
>>>>>>>>>>>       vidioc-dbg-g-chip-info
>>>>>>>>>>>       vidioc-dbg-g-register
>>>>>>>>>>>       vidioc-decoder-cmd
>>>>>>>>>>> +    vidioc-delete-buf
>>>>>>>>>>>       vidioc-dqevent
>>>>>>>>>>>       vidioc-dv-timings-cap
>>>>>>>>>>>       vidioc-encoder-cmd
>>>>>>>>>>> diff --git
>>>>>>>>>>> a/Documentation/userspace-api/media/v4l/vidioc-delete-buf.rst
>>>>>>>>>>> b/Documentation/userspace-api/media/v4l/vidioc-delete-buf.rst
>>>>>>>>>>> new file mode 100644
>>>>>>>>>>> index 000000000000..0e7ce58f91bc
>>>>>>>>>>> --- /dev/null
>>>>>>>>>>> +++ 
>>>>>>>>>>> b/Documentation/userspace-api/media/v4l/vidioc-delete-buf.rst
>>>>>>>>>>> @@ -0,0 +1,51 @@
>>>>>>>>>>> +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
>>>>>>>>>>> +.. c:namespace:: V4L
>>>>>>>>>>> +
>>>>>>>>>>> +.. _VIDIOC_DELETE_BUF:
>>>>>>>>>>> +
>>>>>>>>>>> +************************
>>>>>>>>>>> +ioctl VIDIOC_DELETE_BUF
>>>>>>>>>>> +************************
>>>>>>>>>>> +
>>>>>>>>>>> +Name
>>>>>>>>>>> +====
>>>>>>>>>>> +
>>>>>>>>>>> +VIDIOC_DELETE_BUF - Delete a buffer from a queue
>>>>>>>>>>> +
>>>>>>>>>>> +Synopsis
>>>>>>>>>>> +========
>>>>>>>>>>> +
>>>>>>>>>>> +.. c:macro:: VIDIOC_DELETE_BUF
>>>>>>>>>>> +
>>>>>>>>>>> +``int ioctl(int fd, VIDIOC_DELETE_BUF, struct v4l2_buffer
>>>>>>>>>>> *argp)``
>>>>>>>>>>> +
>>>>>>>>>>> +Arguments
>>>>>>>>>>> +=========
>>>>>>>>>>> +
>>>>>>>>>>> +``fd``
>>>>>>>>>>> +    File descriptor returned by :c:func:`open()`.
>>>>>>>>>>> +
>>>>>>>>>>> +``argp``
>>>>>>>>>>> +    Pointer to struct :c:type:`v4l2_buffer`.
>>>>>>>>>>> +
>>>>>>>>>>> +Description
>>>>>>>>>>> +===========
>>>>>>>>>>> +
>>>>>>>>>>> +Applications can optionally call the :ref:`VIDIOC_DELETE_BUF`
>>>>>>>>>>> ioctl to
>>>>>>>>>>> +delete a buffer from a queue.
>>>>>>>>>>> +
>>>>>>>>>>> +The struct :c:type:`v4l2_buffer` structure is specified in
>>>>>>>>>>> +:ref:`buffer`.
>>>>>>>>>>> +
>>>>>>>>>>> +Return Value
>>>>>>>>>>> +============
>>>>>>>>>>> +
>>>>>>>>>>> +On success 0 is returned, on error -1 and the ``errno``
>>>>>>>>>>> variable is
>>>>>>>>>>> set
>>>>>>>>>>> +appropriately. The generic error codes are described at the
>>>>>>>>>>> +:ref:`Generic Error Codes <gen-errors>` chapter.
>>>>>>>>>>> +
>>>>>>>>>>> +EBUSY
>>>>>>>>>>> +    File I/O is in progress.
>>>>>>>>>>> +
>>>>>>>>>>> +EINVAL
>>>>>>>>>>> +    The buffer ``index`` doesn't exist in the queue.
>>>>>>>>>>> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c
>>>>>>>>>>> b/drivers/media/common/videobuf2/videobuf2-core.c
>>>>>>>>>>> index 899783f67580..aa546c972c3d 100644
>>>>>>>>>>> --- a/drivers/media/common/videobuf2/videobuf2-core.c
>>>>>>>>>>> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
>>>>>>>>>>> @@ -1637,6 +1637,39 @@ int vb2_core_prepare_buf(struct 
>>>>>>>>>>> vb2_queue
>>>>>>>>>>> *q,
>>>>>>>>>>> unsigned int index, void *pb)
>>>>>>>>>>>   }
>>>>>>>>>>>   EXPORT_SYMBOL_GPL(vb2_core_prepare_buf);
>>>>>>>>>>>
>>>>>>>>>>> +int vb2_core_delete_buf(struct vb2_queue *q, unsigned int 
>>>>>>>>>>> index)
>>>>>>>>>>> +{
>>>>>>>>>>> +       struct vb2_buffer *vb;
>>>>>>>>>>> +
>>>>>>>>>>> +       vb = vb2_get_buffer(q, index);
>>>>>>>>>>> +       if (!vb) {
>>>>>>>>>>> +               dprintk(q, 1, "invalid buffer index %d\n",
>>>>>>>>>>> index);
>>>>>>>>>>> +               return -EINVAL;
>>>>>>>>>>> +       }
>>>>>>>>>>> +
>>>>>>>>>>> +       if (vb->state != VB2_BUF_STATE_DEQUEUED) {
>>>>>>>>>>> +               dprintk(q, 1, "can't delete non dequeued buffer
>>>>>>>>>>> index
>>>>>>>>>>> %d\n", index);
>>>>>>>>>>> +               return -EINVAL;
>>>>>>>>>>> +       }
>>>>>>>>>>> +
>>>>>>>>>> I know the driver could implement its own
>>>>>>>>>> v4l2_ioctl_ops->vidioc_delete_buf() that check whether a 
>>>>>>>>>> buffer is
>>>>>>>>>> used by the hardware as a future reference frame.
>>>>>>>>>> But I think we need a flag to let the user know which buffer is
>>>>>>>>>> still
>>>>>>>>>> used by the hardware.
>>>>>>>>>> Alternative ref case is safe, we only know it's existing when
>>>>>>>>>> it is
>>>>>>>>>> dequeued in current V4L2 buffer mechanism.
>>>>>>>>>> While the Golden reference frame, such long term reference frame
>>>>>>>>>> could
>>>>>>>>>> last much longer.
>>>>>>>>>
>>>>>>>>> It is up to userland stack to know frames life time, it got the
>>>>>>>>> information for that.
>>>>>>>>
>>>>>>>> That is true for the stateless codec driver.
>>>>>>>>
>>>>>>>> While application for stateful decoder could never do that. It 
>>>>>>>> also
>>>>>>>> breaks what the document said:
>>>>>>>>
>>>>>>>> "The backing memory of |CAPTURE| buffers that are used as 
>>>>>>>> reference
>>>>>>>> frames by the stream may be read by the hardware even after 
>>>>>>>> they are
>>>>>>>> dequeued. Consequently, the client should avoid writing into this
>>>>>>>> memory
>>>>>>>> while the |CAPTURE| queue is streaming. Failure to observe this 
>>>>>>>> may
>>>>>>>> result in corruption of decoded frames."
>>>>>>>>
>>>>>>>>>
>>>>>>>>>>> +       if (vb->planes[0].mem_priv)
>>>>>>>>>>> +               call_void_vb_qop(vb, buf_cleanup, vb);
>>>>>>>>>>> +
>>>>>>>>>>> +       /* Free MMAP buffers or release USERPTR buffers */
>>>>>>>>>>> +       if (q->memory == VB2_MEMORY_MMAP)
>>>>>>>>>>> +               __vb2_buf_mem_free(vb);
>>>>>>>
>>>>>>> Here is another problem for the existing application, the mmap() 
>>>>>>> from
>>>>>>> the mmap offset or exportbuffer fd would not create a reference to
>>>>>>> buffer in this step(while the exportbuffer would create one 
>>>>>>> itself).
>>>>>>>
>>>>>>> When you delete a buffer, you may not release it from its virtual
>>>>>>> memory space, leaving a corrupted virtual memory space. Also this
>>>>>>> behavior is right, because mmap(2) says:
>>>>>>>
>>>>>>> "After  the  mmap()  call has returned, the file descriptor, fd, 
>>>>>>> can
>>>>>>> be closed immediately without invalidating the map‐ping."
>>>>>>
>>>>>> Existing applications do not call DELETE_BUF ioctl and when call it
>>>>>> they will be aware that the buffer is removed.
>>>>>> I have done it in GStreamer:
>>>>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__gitlab.freedesktop.org_benjamin.gaignard1_gstreamer_-2D_commit_fca0fbc934f4440693ce0ff6c8dc8a2e5f5f17d9&d=DwIDaQ&c=7dfBJ8cXbWjhc0BhImu8wVIoUFmBzj1s88r8EGyM0UY&r=P4xb2_7biqBxD4LGGPrSV6j-jf3C3xlR7PXU-mLTeZE&m=TGH9toTzGRfO5aBsfaMvGbcOw-28q6cPmpX6vScbHjpCtaLtb-RuvBvsJ0z9RvAB&s=Ufl1ccfRZf2EhnfCBvnQzRJV9CDhGxl5spe9WNECspU&e= 
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>> I have read that.
>>>>>
>>>>> There is not a VP8 parser in Gstreamer, while a parser would not work
>>>>> when deal with the secure video(userspace can't access the data
>>>>> context at all).
>>>>>
>>>>> Besides, this adds extra work for the application for a stateful 
>>>>> codec
>>>>> driver. The application need to parser the bitstream and track the 
>>>>> dpb.
>>>>>
>>>>> I don't mind if you could fix the nonfiction mechanism for those
>>>>> non-display frame and internal reference state.
>>>>>
>>>>> That could be requirement for codec firmware that its driver could
>>>>> support this DELETE_BUF ioctl() feature.
>>>>
>>>> Sorry I don't see the link with my patches here...
>>>> I have work on non-secure VP9 on stateless codec.
>>>> DELETE_BUF ioctl is optional and the main goal is to offer a way to
>>>> applications
>>>> to save memory if they know when they could delete buffers without 
>>>> risk.
>>>
>>> I try to explain why I think this design in not "complete". One
>>> problem resolved, more problems would occur.
>>>
>>>
>>> For non-secure video, those applications have worked:
>>>
>>> - It would break what stateful means here, application need to
>>> acquire(parse) the information that driver should offer.
>>>
>>>   Or it would break the decoding model.
>>>
>>> - Your Gstreamer sample code or this design won't work for AV1.
>> why ?
>
> A frame in AV1 could be put to display order with a future frame. That 
> is quite different to those ITU codecs.
>
> Supposing a frame (we call it frame 0) without show_display frame, you 
> could delete it (just want to do that) once it is decoded.
>
> Actually, unless 7 future frames have came and parser has acknowledged 
> them, it is not safe to delete that frame.
>
> Or a show_exist that make frame 0 present.
>
> In my personal opinion, this feature could break many uAPI's, I have 
> said my worrying in the other emails.
>
Of course if the application delete a useful buffer it is a problem but an application issue.
I have test this code using GStreamer with VP9, VP8 and HEVC on Verisilicon driver without issues.
I will be happy if someone could test it on another driver and/or other userlands (like ffmpeg).

>>>
>>> For all the future possible secure video:
>>>
>>> - This feature could never be used from the current design.
>>>
>>>
>>>>
>>>>>
>>>>>>
>>>>>> Regards,
>>>>>> Benjamin
>>>>>>
>>>>>>>
>>>>>>>>>>> +       else if (q->memory == VB2_MEMORY_DMABUF)
>>>>>>>>>>> +               __vb2_buf_dmabuf_put(vb);
>>>>>>>>>>> +       else
>>>>>>>>>>> +               __vb2_buf_userptr_put(vb);
>>>>>>>>>>> +
>>>>>>>>>>> +       vb2_queue_remove_buffer(q, vb);
>>>>>>>>>>> +       kfree(vb);
>>>>>>>>>>> +
>>>>>>>>>>> +       dprintk(q, 2, "buffer %d deleted\n", index);
>>>>>>>>>>> +       return 0;
>>>>>>>>>>> +}
>>>>>>>>>>> +
>>>>>>>>>>>   /*
>>>>>>>>>>>    * vb2_start_streaming() - Attempt to start streaming.
>>>>>>>>>>>    * @q:         videobuf2 queue
>>>>>>>>>>> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c
>>>>>>>>>>> b/drivers/media/common/videobuf2/videobuf2-v4l2.c
>>>>>>>>>>> index 724135d41f7f..cea666c17b41 100644
>>>>>>>>>>> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
>>>>>>>>>>> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
>>>>>>>>>>> @@ -751,6 +751,12 @@ int vb2_prepare_buf(struct vb2_queue *q,
>>>>>>>>>>> struct
>>>>>>>>>>> media_device *mdev,
>>>>>>>>>>>   }
>>>>>>>>>>>   EXPORT_SYMBOL_GPL(vb2_prepare_buf);
>>>>>>>>>>>
>>>>>>>>>>> +int vb2_delete_buf(struct vb2_queue *q, struct v4l2_buffer *b)
>>>>>>>>>>> +{
>>>>>>>>>>> +       return vb2_core_delete_buf(q, b->index);
>>>>>>>>>>> +}
>>>>>>>>>>> +EXPORT_SYMBOL_GPL(vb2_delete_buf);
>>>>>>>>>>> +
>>>>>>>>>>>   int vb2_create_bufs(struct vb2_queue *q, struct
>>>>>>>>>>> v4l2_create_buffers
>>>>>>>>>>> *create)
>>>>>>>>>>>   {
>>>>>>>>>>>          unsigned requested_planes = 1;
>>>>>>>>>>> diff --git a/drivers/media/v4l2-core/v4l2-dev.c
>>>>>>>>>>> b/drivers/media/v4l2-core/v4l2-dev.c
>>>>>>>>>>> index f81279492682..80ace2e1e932 100644
>>>>>>>>>>> --- a/drivers/media/v4l2-core/v4l2-dev.c
>>>>>>>>>>> +++ b/drivers/media/v4l2-core/v4l2-dev.c
>>>>>>>>>>> @@ -720,6 +720,7 @@ static void determine_valid_ioctls(struct
>>>>>>>>>>> video_device *vdev)
>>>>>>>>>>>                  SET_VALID_IOCTL(ops, VIDIOC_PREPARE_BUF,
>>>>>>>>>>> vidioc_prepare_buf);
>>>>>>>>>>>                  SET_VALID_IOCTL(ops, VIDIOC_STREAMON,
>>>>>>>>>>> vidioc_streamon);
>>>>>>>>>>>                  SET_VALID_IOCTL(ops, VIDIOC_STREAMOFF,
>>>>>>>>>>> vidioc_streamoff);
>>>>>>>>>>> +               SET_VALID_IOCTL(ops, VIDIOC_DELETE_BUF,
>>>>>>>>>>> vidioc_delete_buf);
>>>>>>>>>>>          }
>>>>>>>>>>>
>>>>>>>>>>>          if (is_vid || is_vbi || is_meta) {
>>>>>>>>>>> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c
>>>>>>>>>>> b/drivers/media/v4l2-core/v4l2-ioctl.c
>>>>>>>>>>> index a858acea6547..1c737279d3ef 100644
>>>>>>>>>>> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
>>>>>>>>>>> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
>>>>>>>>>>> @@ -2156,6 +2156,15 @@ static int v4l_prepare_buf(const struct
>>>>>>>>>>> v4l2_ioctl_ops *ops,
>>>>>>>>>>>          return ret ? ret : ops->vidioc_prepare_buf(file, 
>>>>>>>>>>> fh, b);
>>>>>>>>>>>   }
>>>>>>>>>>>
>>>>>>>>>>> +static int v4l_delete_buf(const struct v4l2_ioctl_ops *ops,
>>>>>>>>>>> +                         struct file *file, void *fh, void 
>>>>>>>>>>> *arg)
>>>>>>>>>>> +{
>>>>>>>>>>> +       struct v4l2_buffer *b = arg;
>>>>>>>>>>> +       int ret = check_fmt(file, b->type);
>>>>>>>>>>> +
>>>>>>>>>>> +       return ret ? ret : ops->vidioc_delete_buf(file, fh, b);
>>>>>>>>>>> +}
>>>>>>>>>>> +
>>>>>>>>>>>   static int v4l_g_parm(const struct v4l2_ioctl_ops *ops,
>>>>>>>>>>>                                  struct file *file, void *fh,
>>>>>>>>>>> void
>>>>>>>>>>> *arg)
>>>>>>>>>>>   {
>>>>>>>>>>> @@ -2905,6 +2914,7 @@ static const struct v4l2_ioctl_info
>>>>>>>>>>> v4l2_ioctls[] = {
>>>>>>>>>>>          IOCTL_INFO(VIDIOC_ENUM_FREQ_BANDS, 
>>>>>>>>>>> v4l_enum_freq_bands,
>>>>>>>>>>> v4l_print_freq_band, 0),
>>>>>>>>>>>          IOCTL_INFO(VIDIOC_DBG_G_CHIP_INFO, 
>>>>>>>>>>> v4l_dbg_g_chip_info,
>>>>>>>>>>> v4l_print_dbg_chip_info, INFO_FL_CLEAR(v4l2_dbg_chip_info,
>>>>>>>>>>> match)),
>>>>>>>>>>>          IOCTL_INFO(VIDIOC_QUERY_EXT_CTRL, v4l_query_ext_ctrl,
>>>>>>>>>>> v4l_print_query_ext_ctrl, INFO_FL_CTRL |
>>>>>>>>>>> INFO_FL_CLEAR(v4l2_query_ext_ctrl, id)),
>>>>>>>>>>> +       IOCTL_INFO(VIDIOC_DELETE_BUF, v4l_delete_buf,
>>>>>>>>>>> v4l_print_buffer, INFO_FL_QUEUE),
>>>>>>>>>>>   };
>>>>>>>>>>>   #define V4L2_IOCTLS ARRAY_SIZE(v4l2_ioctls)
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/include/media/v4l2-ioctl.h
>>>>>>>>>>> b/include/media/v4l2-ioctl.h
>>>>>>>>>>> index edb733f21604..2f232ed884c7 100644
>>>>>>>>>>> --- a/include/media/v4l2-ioctl.h
>>>>>>>>>>> +++ b/include/media/v4l2-ioctl.h
>>>>>>>>>>> @@ -163,6 +163,8 @@ struct v4l2_fh;
>>>>>>>>>>>    *     :ref:`VIDIOC_CREATE_BUFS <vidioc_create_bufs>` ioctl
>>>>>>>>>>>    * @vidioc_prepare_buf: pointer to the function that 
>>>>>>>>>>> implements
>>>>>>>>>>>    *     :ref:`VIDIOC_PREPARE_BUF <vidioc_prepare_buf>` ioctl
>>>>>>>>>>> + * @vidioc_delete_buf: pointer to the function that implements
>>>>>>>>>>> + *     :ref:`VIDIOC_DELETE_BUF <vidioc_delete_buf>` ioctl
>>>>>>>>>>>    * @vidioc_overlay: pointer to the function that implements
>>>>>>>>>>>    *     :ref:`VIDIOC_OVERLAY <vidioc_overlay>` ioctl
>>>>>>>>>>>    * @vidioc_g_fbuf: pointer to the function that implements
>>>>>>>>>>> @@ -422,6 +424,8 @@ struct v4l2_ioctl_ops {
>>>>>>>>>>>                                    struct v4l2_create_buffers
>>>>>>>>>>> *b);
>>>>>>>>>>>          int (*vidioc_prepare_buf)(struct file *file, void *fh,
>>>>>>>>>>>                                    struct v4l2_buffer *b);
>>>>>>>>>>> +       int (*vidioc_delete_buf)(struct file *file, void *fh,
>>>>>>>>>>> +                                struct v4l2_buffer *b);
>>>>>>>>>>>
>>>>>>>>>>>          int (*vidioc_overlay)(struct file *file, void *fh,
>>>>>>>>>>> unsigned
>>>>>>>>>>> int i);
>>>>>>>>>>>          int (*vidioc_g_fbuf)(struct file *file, void *fh,
>>>>>>>>>>> diff --git a/include/media/videobuf2-core.h
>>>>>>>>>>> b/include/media/videobuf2-core.h
>>>>>>>>>>> index 080b783d608d..0f9e68f76b77 100644
>>>>>>>>>>> --- a/include/media/videobuf2-core.h
>>>>>>>>>>> +++ b/include/media/videobuf2-core.h
>>>>>>>>>>> @@ -840,6 +840,15 @@ int vb2_core_create_bufs(struct vb2_queue
>>>>>>>>>>> *q,
>>>>>>>>>>> enum vb2_memory memory,
>>>>>>>>>>>    */
>>>>>>>>>>>   int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int
>>>>>>>>>>> index,
>>>>>>>>>>> void *pb);
>>>>>>>>>>>
>>>>>>>>>>> +/**
>>>>>>>>>>> + * vb2_core_delete_buf() -
>>>>>>>>>>> + * @q: pointer to &struct vb2_queue with videobuf2 queue.
>>>>>>>>>>> + * @index:     id number of the buffer.
>>>>>>>>>>> + *
>>>>>>>>>>> + *  Return: returns zero on success; an error code otherwise.
>>>>>>>>>>> + */
>>>>>>>>>>> +int vb2_core_delete_buf(struct vb2_queue *q, unsigned int
>>>>>>>>>>> index);
>>>>>>>>>>> +
>>>>>>>>>>>   /**
>>>>>>>>>>>    * vb2_core_qbuf() - Queue a buffer from userspace
>>>>>>>>>>>    *
>>>>>>>>>>> diff --git a/include/media/videobuf2-v4l2.h
>>>>>>>>>>> b/include/media/videobuf2-v4l2.h
>>>>>>>>>>> index 88a7a565170e..3beeb4c735f0 100644
>>>>>>>>>>> --- a/include/media/videobuf2-v4l2.h
>>>>>>>>>>> +++ b/include/media/videobuf2-v4l2.h
>>>>>>>>>>> @@ -114,6 +114,17 @@ int vb2_create_bufs(struct vb2_queue *q,
>>>>>>>>>>> struct
>>>>>>>>>>> v4l2_create_buffers *create);
>>>>>>>>>>>    */
>>>>>>>>>>>   int vb2_prepare_buf(struct vb2_queue *q, struct media_device
>>>>>>>>>>> *mdev,
>>>>>>>>>>>                      struct v4l2_buffer *b);
>>>>>>>>>>> +/**
>>>>>>>>>>> + * vb2_delete_buf() - Delete the buffer from the queue
>>>>>>>>>>> + *
>>>>>>>>>>> + * @q:         pointer to &struct vb2_queue with videobuf2
>>>>>>>>>>> queue.
>>>>>>>>>>> + * @b:         buffer structure passed from userspace to
>>>>>>>>>>> + * &v4l2_ioctl_ops->vidioc_delete_buf handler in driver
>>>>>>>>>>> + *
>>>>>>>>>>> + * The return values from this function are intended to be
>>>>>>>>>>> directly
>>>>>>>>>>> returned
>>>>>>>>>>> + * from &v4l2_ioctl_ops->vidioc_delete_buf handler in driver.
>>>>>>>>>>> + */
>>>>>>>>>>> +int vb2_delete_buf(struct vb2_queue *q, struct v4l2_buffer 
>>>>>>>>>>> *b);
>>>>>>>>>>>
>>>>>>>>>>>   /**
>>>>>>>>>>>    * vb2_qbuf() - Queue a buffer from userspace
>>>>>>>>>>> diff --git a/include/uapi/linux/videodev2.h
>>>>>>>>>>> b/include/uapi/linux/videodev2.h
>>>>>>>>>>> index aee75eb9e686..31bba1915642 100644
>>>>>>>>>>> --- a/include/uapi/linux/videodev2.h
>>>>>>>>>>> +++ b/include/uapi/linux/videodev2.h
>>>>>>>>>>> @@ -2702,6 +2702,8 @@ struct v4l2_create_buffers {
>>>>>>>>>>>   #define VIDIOC_DBG_G_CHIP_INFO  _IOWR('V', 102, struct
>>>>>>>>>>> v4l2_dbg_chip_info)
>>>>>>>>>>>
>>>>>>>>>>>   #define VIDIOC_QUERY_EXT_CTRL  _IOWR('V', 103, struct
>>>>>>>>>>> v4l2_query_ext_ctrl)
>>>>>>>>>>> +#define VIDIOC_DELETE_BUF      _IOWR('V', 104, struct
>>>>>>>>>>> v4l2_buffer)
>>>>>>>>>>> +
>>>>>>>>>>>
>>>>>>>>>>>   /* Reminder: when adding new ioctls please add support for
>>>>>>>>>>> them to
>>>>>>>>>>> drivers/media/v4l2-core/v4l2-compat-ioctl32.c as well! */
>>>>>>>>>>> -- 
>>>>>>>>>>> 2.39.2
>>>>>>>>>>>
>>>>>>>> -- 
>>>>>>>> Hsia-Jun(Randy) Li
>>>>>>>>
> -- 
> Hsia-Jun(Randy) Li

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