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

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Message-ID: <20231108085016.3kmhmdroh4qs53f5@chromium.org>
Date:   Wed, 8 Nov 2023 08:50:16 +0000
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 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?

> +
> +	q->bufs[index] = vb;
> +	vb->index = index;
> +	vb->vb2_queue = q;
> +}
[snip]
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index d19d82a75ac6..2ffb097bf00a 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -377,6 +377,12 @@ static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct media_device *md
>  		return -EINVAL;
>  	}
>  
> +	vb = vb2_get_buffer(q, b->index);
> +	if (!vb) {
> +		dprintk(q, 1, "%s: buffer %u is NULL\n", opname,  b->index);
> +		return -EINVAL;
> +	}
> +

Is this a leftover from earlier revisions? I think it shouldn't be
needed anymore after the previous patch which changed the function to
get vb as an argument.

Best regards,
Tomasz