linux-kernel - Re: [PATCH v14 05/56] media: videobuf2: Access vb2_queue bufs array through helper functions

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Date:   Thu, 9 Nov 2023 13:27:22 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Benjamin Gaignard <benjamin.gaignard@...labora.com>
Cc:     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 05/56] media: videobuf2: Access vb2_queue bufs array
 through helper functions

On Wed, Nov 8, 2023 at 7:24 PM Benjamin Gaignard
<benjamin.gaignard@...labora.com> wrote:
>
>
> Le 08/11/2023 à 09:50, Tomasz Figa a écrit :
> > On Tue, Oct 31, 2023 at 05:30:13PM +0100, Benjamin Gaignard wrote:
> >> This patch adds 2 helpers functions to add and remove vb2 buffers
> >> from a queue. With these 2 and vb2_get_buffer(), bufs field of
> >> struct vb2_queue becomes like a private member of the structure.
> >>
> >> After each call to vb2_get_buffer() we need to be sure that we get
> >> a valid pointer in preparation for when buffers can be deleted.
> >>
> >> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
> >> ---
> >>   .../media/common/videobuf2/videobuf2-core.c   | 151 +++++++++++++-----
> >>   .../media/common/videobuf2/videobuf2-v4l2.c   |  50 ++++--
> >>   2 files changed, 149 insertions(+), 52 deletions(-)
> >>
> >> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> >> index 968b7c0e7934..b406a30a9b35 100644
> >> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> >> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> >> @@ -408,6 +408,31 @@ static void init_buffer_cache_hints(struct vb2_queue *q, struct vb2_buffer *vb)
> >>              vb->skip_cache_sync_on_finish = 1;
> >>   }
> >>
> >> +/**
> >> + * vb2_queue_add_buffer() - add a buffer to a queue
> >> + * @q:      pointer to &struct vb2_queue with videobuf2 queue.
> >> + * @vb:     pointer to &struct vb2_buffer to be added to the queue.
> >> + * @index: index where add vb2_buffer in the queue
> >> + */
> >> +static void vb2_queue_add_buffer(struct vb2_queue *q, struct vb2_buffer *vb, unsigned int index)
> >> +{
> >> +    WARN_ON(index >= VB2_MAX_FRAME || q->bufs[index]);
> > nit: Would it make sense to also ensure that vb->vb2_queue is NULL?
>
> Since vb->vb2_queue and q->bufs[index] are always set and clear in the same
> functions I don't think it is useful to test the both here.
>

Well, they are if the caller is not buggy. But I suppose the check is
to detect buggy callers?

For example, an m2m driver could accidentally call this on a buffer
that was already added to another queue.

Best regards,
Tomasz