Message-ID: <CAAFQd5Cvdm12h-HOyKaxpu+s9x5sHEZ+ShSd5twYNpWBDEzWig@mail.gmail.com>
Date:   Fri, 10 Nov 2023 18:19:49 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        mchehab@...nel.org, m.szyprowski@...sung.com, ming.qian@....com,
        ezequiel@...guardiasur.com.ar, p.zabel@...gutronix.de,
        gregkh@...uxfoundation.org, hverkuil-cisco@...all.nl,
        nicolas.dufresne@...labora.com, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, linux-staging@...ts.linux.dev,
        kernel@...labora.com
Subject: Re: [PATCH v14 54/56] media: v4l2: Add DELETE_BUFS ioctl

On Fri, Nov 10, 2023 at 6:14 PM Hans Verkuil <hverkuil@...all.nl> wrote:
>
> On 10/11/2023 09:58, Tomasz Figa wrote:
> > On Thu, Nov 9, 2023 at 7:10 PM Benjamin Gaignard
> > <benjamin.gaignard@...labora.com> wrote:
> >>
> >>
> >> Le 09/11/2023 à 10:30, Tomasz Figa a écrit :
> >>> On Tue, Oct 31, 2023 at 05:31:02PM +0100, Benjamin Gaignard wrote:
> >>>> VIDIOC_DELETE_BUFS ioctl allows to delete buffers from a queue.
> >>>> The number of buffers to delete in given by count field of
> >>>> struct v4l2_delete_buffers and the range start at the index
> >>>> specified in the same structure.
> >>>>
> >>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
> >>>> ---
> >>>>   .../userspace-api/media/v4l/user-func.rst     |  1 +
> >>>>   .../media/v4l/vidioc-delete-bufs.rst          | 80 +++++++++++++++++++
> >>>>   .../media/v4l/vidioc-reqbufs.rst              |  1 +
> >>>>   .../media/common/videobuf2/videobuf2-core.c   | 30 +++++++
> >>>>   .../media/common/videobuf2/videobuf2-v4l2.c   | 20 +++++
> >>>>   drivers/media/v4l2-core/v4l2-dev.c            |  1 +
> >>>>   drivers/media/v4l2-core/v4l2-ioctl.c          | 17 ++++
> >>>>   include/media/v4l2-ioctl.h                    |  4 +
> >>>>   include/media/videobuf2-core.h                | 12 +++
> >>>>   include/media/videobuf2-v4l2.h                | 13 +++
> >>>>   include/uapi/linux/videodev2.h                | 17 ++++
> >>>>   11 files changed, 196 insertions(+)
> >>>>   create mode 100644 Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst
> >>>>
> >>>> diff --git a/Documentation/userspace-api/media/v4l/user-func.rst b/Documentation/userspace-api/media/v4l/user-func.rst
> >>>> index 15ff0bf7bbe6..3fd567695477 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-bufs
> >>>>       vidioc-dqevent
> >>>>       vidioc-dv-timings-cap
> >>>>       vidioc-encoder-cmd
> >>>> diff --git a/Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst
> >>>> new file mode 100644
> >>>> index 000000000000..4791df1395d6
> >>>> --- /dev/null
> >>>> +++ b/Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst
> >>>> @@ -0,0 +1,80 @@
> >>>> +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
> >>>> +.. c:namespace:: V4L
> >>>> +
> >>>> +.. _VIDIOC_DELETE_BUFS:
> >>>> +
> >>>> +************************
> >>>> +ioctl VIDIOC_DELETE_BUFS
> >>>> +************************
> >>>> +
> >>>> +Name
> >>>> +====
> >>>> +
> >>>> +VIDIOC_DELETE_BUFS - Deletes buffers from a queue
> >>>> +Drivers using this feature must expose the ``V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS``
> >>>> +capability on the queue :c:func:`VIDIOC_REQBUFS` or :c:func:`VIDIOC_CREATE_BUFS`
> >>>> +are invoked.
> >>>> +
> >>>> +Synopsis
> >>>> +========
> >>>> +
> >>>> +.. c:macro:: VIDIOC_DELETE_BUFs
> >>>> +
> >>>> +``int ioctl(int fd, VIDIOC_DELETE_BUFs, struct v4l2_delete_buffers *argp)``
> >>>> +
> >>>> +Arguments
> >>>> +=========
> >>>> +
> >>>> +``fd``
> >>>> +    File descriptor returned by :c:func:`open()`.
> >>>> +
> >>>> +``argp``
> >>>> +    Pointer to struct :c:type:`v4l2_delete_buffers`.
> >>>> +
> >>>> +Description
> >>>> +===========
> >>>> +
> >>>> +Applications can optionally call the :ref:`VIDIOC_DELETE_BUFS` ioctl to
> >>>> +delete buffers from a queue.
> >>>> +
> >>>> +.. c:type:: v4l2_delete_buffers
> >>>> +
> >>>> +.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
> >>>> +
> >>>> +.. flat-table:: struct v4l2_delete_buffers
> >>>> +    :header-rows:  0
> >>>> +    :stub-columns: 0
> >>>> +    :widths:       1 1 2
> >>>> +
> >>>> +    * - __u32
> >>>> +      - ``index``
> >>>> +      - The starting buffer index to delete.
> >>>> +    * - __u32
> >>>> +      - ``count``
> >>>> +      - The number of buffers to be deleted with indices 'index' until 'index + count - 1'.
> >>>> +        All buffers in this range must be valid and in DEQUEUED state.
> >>> I wonder if this wouldn't be an inconvenience for the userspace. Would
> >>> there be anything wrong with allowing ranges with holes?
> >>> (Agreed about the DEQUEUED part of course.)
> >>
> >> For me a range as to be valid but the matter of taste.
> >>
> >
> > @Hans Verkuil do you have an opinion?
> > I could imagine that applications may want to just delete multiple
> > disjoint ranges in one ioctl, which wouldn't be possible if we
> > prohibit holes in the ranges.
>
> First of all I want to state that I am mostly concentrating on patches 1-50 to get
> those merged first. The actual delete_bufs patches will need more review from me.

Makes sense. Thanks for the heads up. I did review the implementation
and it looks reasonable to me. I think the initial refactoring did a
lot of good to the code to make it much easier to implement the actual
deletion.

>
> That said, while I do not have a very strong opinion on this, I do feel it is better
> to be strict about this. It can always be relaxed later. Deleting buffers is an
> important operation, and userspace should know what it is doing. Deleting non-existing
> buffers seems iffy to me.

I don't have a strong opinion, so I guess I'm okay with that, if you
feel strongly about it. I'm just curious if there would be any
practical issue with it. After all, even if we disallow holes in the
deleted range, there are still many ways the userspace can be buggy
about it, e.g. by deleting buffers belonging to two adjacent ranges.
(On the other hand, the less ways to make mistakes, the better, I
guess...)

>
> Regards,
>
>         Hans
>
> >
> >>>
> >>>> +        In error case errno is set to ``EINVAL`` error code and index returns the index of
> >>>> +        the invalid buffer.
> >>>> +        If count and index are set to 0 :ref:`VIDIOC_DELETE_BUFS` will return 0.
> >>> Hmm, do we care about index if count is zero?
> >>
> >> No we don't I will change that.
> >>
> >>>
> >>>> +    * - __u32
> >>>> +      - ``type``
> >>>> +      - Type of the stream or buffers, this is the same as the struct
> >>>> +    :c:type:`v4l2_format` ``type`` field. See
> >>>> +    :c:type:`v4l2_buf_type` for valid values.
> >>>> +    * - __u32
> >>>> +      - ``reserved``\ [13]
> >>>> +      - A place holder for future extensions. Drivers and applications
> >>>> +    must set the array to zero.
> >>>> +
> >>>> +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/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> >>>> index 0b3a41a45d05..14d4a49c2945 100644
> >>>> --- a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> >>>> +++ b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> >>>> @@ -121,6 +121,7 @@ aborting or finishing any DMA in progress, an implicit
> >>>>   .. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF:
> >>>>   .. _V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS:
> >>>>   .. _V4L2-BUF-CAP-SUPPORTS-MAX-NUM-BUFFERS:
> >>>> +.. _V4L2-BUF-CAP-SUPPORTS-DELETE-BUFS:
> >>>>
> >>>>   .. raw:: latex
> >>>>
> >>>> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> >>>> index 010a8bca0240..7068930a0ba6 100644
> >>>> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> >>>> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> >>>> @@ -1665,6 +1665,36 @@ int vb2_core_prepare_buf(struct vb2_queue *q, struct vb2_buffer *vb, void *pb)
> >>>>   }
> >>>>   EXPORT_SYMBOL_GPL(vb2_core_prepare_buf);
> >>>>
> >>>> +int vb2_core_delete_bufs(struct vb2_queue *q, unsigned int start, unsigned int count)
> >>>> +{
> >>>> +    unsigned int i, ret = 0;
> >>>> +
> >>>> +    if (start == 0 && count == 0)
> >>> I guess related to the earlier comment, but why do we care about start
> >>> being zero?
> >>>
> >>>> +            return 0;
> >>>> +
> >>>> +    mutex_lock(&q->mmap_lock);
> >>>> +
> >>>> +    for (i = start; i < start + count && i < q->max_num_buffers; i++) {
> >>>> +            struct vb2_buffer *vb = vb2_get_buffer(q, i);
> >>>> +
> >>>> +            if (!vb) {
> >>>> +                    ret = -EINVAL;
> >>>> +                    goto unlock;
> >>>> +            }
> >>>> +            if (vb->state != VB2_BUF_STATE_DEQUEUED) {
> >>>> +                    ret = -EINVAL;
> >>>> +                    goto unlock;
> >>>> +            }
> >>>> +    }
> >>>> +    __vb2_queue_free(q, start, count);
> >>>> +    dprintk(q, 2, "buffers deleted\n");
> >>>> +
> >>>> +unlock:
> >>>> +    mutex_unlock(&q->mmap_lock);
> >>>> +    return ret;
> >>>> +}
> >>>> +EXPORT_SYMBOL_GPL(vb2_core_delete_bufs);
> >>>> +
> >>>>   /*
> >>>>    * 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 56daf3b5b2ba..f003618efbc1 100644
> >>>> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> >>>> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> >>>> @@ -694,6 +694,8 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
> >>>>      if (q->supports_requests)
> >>>>              *caps |= V4L2_BUF_CAP_SUPPORTS_REQUESTS;
> >>>>   #endif
> >>>> +    if (q->supports_delete_bufs)
> >>>> +            *caps |= V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS;
> >>>>   }
> >>>>
> >>>>   static void validate_memory_flags(struct vb2_queue *q,
> >>>> @@ -751,6 +753,12 @@ int vb2_prepare_buf(struct vb2_queue *q, struct media_device *mdev,
> >>>>   }
> >>>>   EXPORT_SYMBOL_GPL(vb2_prepare_buf);
> >>>>
> >>>> +int vb2_delete_bufs(struct vb2_queue *q, struct v4l2_delete_buffers *d)
> >>>> +{
> >>>> +    return vb2_core_delete_bufs(q, d->index, d->count);
> >>>> +}
> >>>> +EXPORT_SYMBOL_GPL(vb2_delete_bufs);
> >>>> +
> >>>>   int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
> >>>>   {
> >>>>      unsigned requested_planes = 1;
> >>>> @@ -1012,6 +1020,18 @@ EXPORT_SYMBOL_GPL(vb2_poll);
> >>>>
> >>>>   /* vb2 ioctl helpers */
> >>>>
> >>>> +int vb2_ioctl_delete_bufs(struct file *file, void *priv,
> >>>> +                      struct v4l2_delete_buffers *p)
> >>>> +{
> >>>> +    struct video_device *vdev = video_devdata(file);
> >>>> +
> >>>> +    if (vb2_queue_is_busy(vdev->queue, file))
> >>>> +            return -EBUSY;
> >>>> +
> >>>> +    return vb2_delete_bufs(vdev->queue, p);
> >>>> +}
> >>>> +EXPORT_SYMBOL_GPL(vb2_ioctl_delete_bufs);
> >>>> +
> >>>>   int vb2_ioctl_reqbufs(struct file *file, void *priv,
> >>>>                        struct v4l2_requestbuffers *p)
> >>>>   {
> >>>> diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
> >>>> index f81279492682..215654fd6581 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_BUFS, vidioc_delete_bufs);
> >>>>      }
> >>>>
> >>>>      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 4d90424cbfc4..e9dcf439f9f3 100644
> >>>> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> >>>> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> >>>> @@ -489,6 +489,13 @@ static void v4l_print_create_buffers(const void *arg, bool write_only)
> >>>>      v4l_print_format(&p->format, write_only);
> >>>>   }
> >>>>
> >>>> +static void v4l_print_delete_buffers(const void *arg, bool write_only)
> >>>> +{
> >>>> +    const struct v4l2_delete_buffers *p = arg;
> >>>> +
> >>>> +    pr_cont("index=%u, count=%u\n", p->index, p->count);
> >>>> +}
> >>>> +
> >>>>   static void v4l_print_streamparm(const void *arg, bool write_only)
> >>>>   {
> >>>>      const struct v4l2_streamparm *p = arg;
> >>>> @@ -2161,6 +2168,15 @@ 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_bufs(const struct v4l2_ioctl_ops *ops,
> >>>> +                       struct file *file, void *fh, void *arg)
> >>>> +{
> >>>> +    struct v4l2_delete_buffers *delete = arg;
> >>>> +    int ret = check_fmt(file, delete->type);
> >>> Should we also have
> >>>
> >>>       memset_after(delete, 0, type);
> >>>
> >>> here similar to how other ioctl handlers clear the reserved fields?
> >>
> >> I will add it.
> >>
> >>>
> >>>> +
> >>>> +    return ret ? ret : ops->vidioc_delete_bufs(file, fh, delete);
> >>>> +}
> >>>> +
> >>>>   static int v4l_g_parm(const struct v4l2_ioctl_ops *ops,
> >>>>                              struct file *file, void *fh, void *arg)
> >>>>   {
> >>>> @@ -2910,6 +2926,7 @@ 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_BUFS, v4l_delete_bufs, v4l_print_delete_buffers, INFO_FL_PRIO | INFO_FL_QUEUE | INFO_FL_CLEAR(v4l2_delete_buffers, type)),
> >>>>   };
> >>>>   #define V4L2_IOCTLS ARRAY_SIZE(v4l2_ioctls)
> >>>>
> >>>> diff --git a/include/media/v4l2-ioctl.h b/include/media/v4l2-ioctl.h
> >>>> index edb733f21604..55afbde54211 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_bufs: pointer to the function that implements
> >>>> + *  :ref:`VIDIOC_DELETE_BUFS <vidioc_delete_bufs>` 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_bufs)(struct file *file, void *fh,
> >>>> +                              struct v4l2_delete_buffers *d);
> >>>>
> >>>>      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 288477075a0e..db3bd986624e 100644
> >>>> --- a/include/media/videobuf2-core.h
> >>>> +++ b/include/media/videobuf2-core.h
> >>>> @@ -507,6 +507,7 @@ struct vb2_buf_ops {
> >>>>    * @supports_requests: this queue supports the Request API.
> >>>>    * @requires_requests: this queue requires the Request API. If this is set to 1,
> >>>>    *         then supports_requests must be set to 1 as well.
> >>>> + * @supports_delete_bufs: this queue supports DELETE_BUFS ioctl.
> >>>>    * @uses_qbuf:     qbuf was used directly for this queue. Set to 1 the first
> >>>>    *         time this is called. Set to 0 when the queue is canceled.
> >>>>    *         If this is 1, then you cannot queue buffers from a request.
> >>>> @@ -595,6 +596,7 @@ struct vb2_queue {
> >>>>      unsigned int               quirk_poll_must_check_waiting_for_buffers:1;
> >>>>      unsigned int                    supports_requests:1;
> >>>>      unsigned int                    requires_requests:1;
> >>>> +    unsigned int                    supports_delete_bufs:1;
> >>>>      unsigned int                    uses_qbuf:1;
> >>>>      unsigned int                    uses_requests:1;
> >>>>      unsigned int                    allow_cache_hints:1;
> >>>> @@ -846,6 +848,16 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
> >>>>    */
> >>>>   int vb2_core_prepare_buf(struct vb2_queue *q, struct vb2_buffer *vb, void *pb);
> >>>>
> >>>> +/**
> >>>> + * vb2_core_delete_bufs() -
> >>>> + * @q:              pointer to &struct vb2_queue with videobuf2 queue.
> >>>> + * @start:  first index of the range of buffers to delete.
> >>>> + * @count:  number of buffers to delete.
> >>>> + *
> >>>> + *  Return: returns zero on success; an error code otherwise.
> >>>> + */
> >>>> +int vb2_core_delete_bufs(struct vb2_queue *q, unsigned int start, unsigned int count);
> >>>> +
> >>>>   /**
> >>>>    * vb2_core_qbuf() - Queue a buffer from userspace
> >>>>    *
> >>>> diff --git a/include/media/videobuf2-v4l2.h b/include/media/videobuf2-v4l2.h
> >>>> index 5a845887850b..79cea8459f52 100644
> >>>> --- a/include/media/videobuf2-v4l2.h
> >>>> +++ b/include/media/videobuf2-v4l2.h
> >>>> @@ -118,6 +118,17 @@ 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_bufs() - Delete buffers from the queue
> >>>> + *
> >>>> + * @q:              pointer to &struct vb2_queue with videobuf2 queue.
> >>>> + * @d:              delete parameter, passed from userspace to
> >>>> + *          &v4l2_ioctl_ops->vidioc_delete_bufs handler in driver
> >>>> + *
> >>>> + * The return values from this function are intended to be directly returned
> >>>> + * from &v4l2_ioctl_ops->vidioc_delete_bufs handler in driver.
> >>>> + */
> >>>> +int vb2_delete_bufs(struct vb2_queue *q, struct v4l2_delete_buffers *d);
> >>>>
> >>>>   /**
> >>>>    * vb2_qbuf() - Queue a buffer from userspace
> >>>> @@ -334,6 +345,8 @@ int vb2_ioctl_streamon(struct file *file, void *priv, enum v4l2_buf_type i);
> >>>>   int vb2_ioctl_streamoff(struct file *file, void *priv, enum v4l2_buf_type i);
> >>>>   int vb2_ioctl_expbuf(struct file *file, void *priv,
> >>>>      struct v4l2_exportbuffer *p);
> >>>> +int vb2_ioctl_delete_bufs(struct file *file, void *priv,
> >>>> +                      struct v4l2_delete_buffers *p);
> >>>>
> >>>>   /* struct v4l2_file_operations helpers */
> >>>>
> >>>> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> >>>> index 13ddb5abf584..96e105149906 100644
> >>>> --- a/include/uapi/linux/videodev2.h
> >>>> +++ b/include/uapi/linux/videodev2.h
> >>>> @@ -1036,6 +1036,7 @@ struct v4l2_requestbuffers {
> >>>>   #define V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF (1 << 5)
> >>>>   #define V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS             (1 << 6)
> >>>>   #define V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS              (1 << 7)
> >>>> +#define V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS           (1 << 8)
> >>>>
> >>>>   /**
> >>>>    * struct v4l2_plane - plane info for multi-planar buffers
> >>>> @@ -2622,6 +2623,20 @@ struct v4l2_create_buffers {
> >>>>      __u32                   reserved[5];
> >>>>   };
> >>>>
> >>>> +/**
> >>>> + * struct v4l2_delete_buffers - VIDIOC_DELETE_BUFS argument
> >>>> + * @index:  the first buffer to be deleted
> >>>> + * @count:  number of buffers to delete
> >>>> + * @type:   enum v4l2_buf_type
> >>>> + * @reserved:       future extensions
> >>>> + */
> >>>> +struct v4l2_delete_buffers {
> >>>> +    __u32                   index;
> >>>> +    __u32                   count;
> >>>> +    __u32                   type;
> >>>> +    __u32                   reserved[13];
> >>>> +};
> >>>> +
> >>>>   /*
> >>>>    * I O C T L   C O D E S   F O R   V I D E O   D E V I C E S
> >>>>    *
> >>>> @@ -2721,6 +2736,8 @@ 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_BUFS  _IOWR('V', 104, struct v4l2_delete_buffers)
> >>>> +
> >>>>
> >>>>   /* Reminder: when adding new ioctls please add support for them to
> >>>>      drivers/media/v4l2-core/v4l2-compat-ioctl32.c as well! */
> >>> Do we also need to add support for the new ioctl in there?
> >>
> >> It only use _u32, is aligned on cache boundary and doesn't use pointer.
> >> For me 32 and 64 bits structures are identical so it doesn't need to be convert.
> >> Maybe I'm wrong when testing it with pahole ?
> >
> > Ah, right. I double checked the compat code and indeed if an ioctl is
> > not listed there, it will just use the default copy_from_user, so we
> > should be good.
> >
> > Maybe one day we should update that comment to explain how to check if
> > it's necessary to add a compat handler.
> >
> > Best regards,
> > Tomasz
>

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