linux-kernel - Re: [RFC 3/5] dma-buf/fence: add .get

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Date:	Thu, 23 Jun 2016 21:40:38 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Gustavo Padovan <gustavo@...ovan.org>
Cc:	dri-devel@...ts.freedesktop.org, marcheu@...gle.com,
	Daniel Stone <daniels@...labora.com>, seanpaul@...gle.com,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	linux-kernel@...r.kernel.org, laurent.pinchart@...asonboard.com,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	John Harrison <John.C.Harrison@...el.com>, m.chehab@...sung.com
Subject: Re: [RFC 3/5] dma-buf/fence: add .get_fences() ops

On Thu, Jun 23, 2016 at 12:29:48PM -0300, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
> 
> get_fences() should return a copy of all fences in the fence as some
> fence subclass (such as fence_array) can store more than one fence at
> time.
> 
> Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
> ---
>  drivers/dma-buf/fence.c | 14 ++++++++++++++
>  include/linux/fence.h   |  3 +++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/drivers/dma-buf/fence.c b/drivers/dma-buf/fence.c
> index 4e61afb..f4094fd 100644
> --- a/drivers/dma-buf/fence.c
> +++ b/drivers/dma-buf/fence.c
> @@ -185,6 +185,20 @@ void fence_release(struct kref *kref)
>  }
>  EXPORT_SYMBOL(fence_release);
>  
> +struct fence **fence_get_fences(struct fence *fence)

Returning an array, but not telling the caller how many elements in the
array?

> +{
> +	if (fence->ops->get_fences) {
> +		return fence->ops->get_fences(fence);
> +	} else {
> +		struct fence **fences = kmalloc(sizeof(**fences), GFP_KERNEL);

One too many * (=> sizeof(struct fence), not sizeof(struct fence *))

return kmemdup(&fence, sizeof(fence), GFP_KERNEL);

The documentation should emphasize that the fences in the
returned array have a "borrowed" reference (i.e. it does not return a
new reference to each fence).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre