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Date:   Fri, 30 Jun 2023 17:43:51 +0800
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Subject: Re: [PATCH v3 10/11] media: v4l2: Add DELETE_BUF ioctl
Content-Language: en-GB
From:   Hsia-Jun Li <Randy.Li@synaptics.com>
To:     Benjamin Gaignard <benjamin.gaignard@collabora.com>
Cc:     linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        p.zabel@pengutronix.de, ming.qian@nxp.com,
        hverkuil-cisco@xs4all.nl, gregkh@linuxfoundation.org,
        ezequiel@vanguardiasur.com.ar,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, linux-arm-msm@vger.kernel.org,
        linux-rockchip@lists.infradead.org, nicolas.dufresne@collabora.com,
        linux-staging@lists.linux.dev, kernel@collabora.com,
        mchehab@kernel.org, tfiga@chromium.org, m.szyprowski@samsung.com,
        ayaka <ayaka@soulik.info>
References: <20230622131349.144160-1-benjamin.gaignard@collabora.com>
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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@collabora.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."

>>>> +       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