linux-kernel - Re: [PATCH v2 03/15] media: videobuf2: Allow exporting of a struct dmabuf

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Message-ID: <72f83177-cd34-480a-afcc-a79f85219751@gmx.net>
Date:   Tue, 14 Nov 2023 20:41:11 +0100
From:   Stefan Wahren <wahrenst@....net>
To:     Umang Jain <umang.jain@...asonboard.com>,
        linux-media@...r.kernel.org, kernel-list@...pberrypi.com,
        linux-kernel@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-staging@...ts.linux.dev
Cc:     Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        "Ricardo B . Marliere" <ricardo@...liere.net>,
        Dan Carpenter <error27@...il.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.org>
Subject: Re: [PATCH v2 03/15] media: videobuf2: Allow exporting of a struct
 dmabuf

Hi Umang,

Am 09.11.23 um 22:02 schrieb Umang Jain:
> From: Dave Stevenson <dave.stevenson@...pberrypi.org>
>
> videobuf2 only allowed exporting a dmabuf as a file descriptor,
> but there are instances where having the struct dma_buf is
> useful within the kernel.
>
> Split the current implementation into two, one step which
> exports a struct dma_buf, and the second which converts that
> into an fd.
>
> Signed-off-by: Dave Stevenson <dave.stevenson@...pberrypi.org>
> Signed-off-by: Umang Jain <umang.jain@...asonboard.com>
> ---

...

> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 4b6a9d2ea372..cba4e495f6a2 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -925,6 +925,21 @@ int vb2_core_streamon(struct vb2_queue *q, unsigned int type);
>    */
>   int vb2_core_streamoff(struct vb2_queue *q, unsigned int type);
>
> +/**
> + * vb2_core_expbuf_dmabuf() - Export a buffer as a dma_buf structure
> + * @q:         videobuf2 queue
> + * @type:      buffer type
> + * @index:     id number of the buffer
> + * @plane:     index of the plane to be exported, 0 for single plane queues
> + * @flags:     flags for newly created file, currently only O_CLOEXEC is
> + *             supported, refer to manual of open syscall for more details

i think "newly created file" could be confusing here

> + *
> + * Return: Returns the dmabuf pointer
> + */
> +struct dma_buf *vb2_core_expbuf_dmabuf(struct vb2_queue *q, unsigned int type,
> +				       unsigned int index, unsigned int plane,
> +				       unsigned int flags);
> +
>   /**
>    * vb2_core_expbuf() - Export a buffer as a file descriptor.
>    * @q:		pointer to &struct vb2_queue with videobuf2 queue.