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Date:   Mon, 17 Jul 2023 10:16:52 +0800
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Subject: Re: [PATCH v3 10/11] media: v4l2: Add DELETE_BUF ioctl
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To:     Tomasz Figa <tfiga@chromium.org>
Cc:     Benjamin Gaignard <benjamin.gaignard@collabora.com>,
        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, m.szyprowski@samsung.com,
        ayaka <ayaka@soulik.info>
References: <20230622131349.144160-1-benjamin.gaignard@collabora.com>
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 <54833256-7d88-9316-4f0f-b8c57552cd7b@synaptics.com>
 <20230713090944.3gxrxt7lqnozhu7r@chromium.org>
From:   Hsia-Jun Li <Randy.Li@synaptics.com>
In-Reply-To: <20230713090944.3gxrxt7lqnozhu7r@chromium.org>
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On 7/13/23 17:09, Tomasz Figa wrote:
> CAUTION: Email originated externally, do not click links or open attachments unless you recognize the sender and know the content is safe.
>
>
> On Fri, Jun 30, 2023 at 05:43:51PM +0800, Hsia-Jun Li wrote:
>> 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.
> What do you mean? __vb2_buf_mem_free() doesn't unconditionally free the
> memory, it just decrements a reference counter.

struct dma_buf_ops->mmap() may not increase a reference to its buffer.

While struct vb2_mem_ops->get_dmabuf() would.

> The VMA holds its own,
> so the buffer is only fully released when the application calls
> munmap().

DELETE_BUF ioctl() didn't answer to this problem. Should the DELETE_BUF 
ioctl() make the no other user could access to this.

>
> Best regards,
> Tomasz
>
>> 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
>>
-- 
Hsia-Jun(Randy) Li