Re: [PATCH v3 10/11] media: v4l2: Add DELETE_BUF ioctl

[Benjamin Gaignard <benjamin.gaignard@collabora.com>]

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@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."

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://gitlab.freedesktop.org/benjamin.gaignard1/gstreamer/-/commit/fca0fbc934f4440693ce0ff6c8dc8a2e5f5f17d9

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
>>