Message-ID: <08588eb0-0e3f-828a-65be-50460560095d@synaptics.com>
Date:   Fri, 28 Jul 2023 15:26:28 +0800
From:   Hsia-Jun Li <Randy.Li@...aptics.com>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        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, m.szyprowski@...sung.com,
        ayaka <ayaka@...lik.info>
Subject: Re: [PATCH v3 10/11] media: v4l2: Add DELETE_BUF ioctl



On 7/28/23 14:57, 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 Mon, Jul 17, 2023 at 11:17 AM Hsia-Jun Li <Randy.Li@...aptics.com> wrote:
>>
>>
>> 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@...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.
>>> 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.
I think we are talking the same refcount.
That is vb2_vmarea_handler->refcount.
While, I am thinking about refcount from vb2_dc_buf.
> 
> Both V4L2 mmap() and DMA-buf mmap() of buffers exported from V4L2
> would increase a reference to the buffer. They both lead to
> vb2_{dc,sg,vmalloc}_mmap() which open the VMA, which in turn calls
> vb2_common_vm_open() that increases the buffer refcount.
> 
> Best regards,
> Tomasz
> 
>>
>> 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
>>

-- 
Hsia-Jun(Randy) Li

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