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Subject: Re: [PATCH] dma-buf: remove restriction of IOCTL:DMA_BUF_SET_NAME
To:     guangming.cao@mediatek.com, Sumit Semwal <sumit.semwal@linaro.org>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@vger.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <dri-devel@lists.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@lists.linaro.org>,
        open list <linux-kernel@vger.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@lists.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@lists.infradead.org>
Cc:     wsd_upstream@mediatek.com
References: <20211009024733.65676-1-guangming.cao@mediatek.com>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <c23181a5-b75b-c04b-7cc4-020f2b2b44c1@infradead.org>
Date:   Fri, 8 Oct 2021 21:41:04 -0700
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On 10/8/21 7:47 PM, guangming.cao@mediatek.com wrote:
> From: Guangming Cao <Guangming.Cao@mediatek.com>
> 
> If dma-buf don't want userspace users to touch the dmabuf buffer,
> it seems we should add this restriction into dma_buf_ops.mmap,
> not in this IOCTL:DMA_BUF_SET_NAME.
> 
> With this restriction, we can only know the kernel users of the dmabuf
> by attachments.
> However, for many userspace users, such as userpsace users of dma_heap,
> they also need to mark the usage of dma-buf, and they don't care about
> who attached to this dmabuf, and seems it's no meaning to waitting for

                                                          to be waiting for

> IOCTL:DMA_BUF_SET_NAME rather than mmap.
> 
> Signed-off-by: Guangming Cao <Guangming.Cao@mediatek.com>
> ---
>   drivers/dma-buf/dma-buf.c | 14 ++------------
>   1 file changed, 2 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 511fe0d217a0..afbd0a226639 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -325,10 +325,8 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
>   
>   /**
>    * dma_buf_set_name - Set a name to a specific dma_buf to track the usage.
> - * The name of the dma-buf buffer can only be set when the dma-buf is not
> - * attached to any devices. It could theoritically support changing the
> - * name of the dma-buf if the same piece of memory is used for multiple
> - * purpose between different devices.
> + * It could theoritically support changing the name of the dma-buf if the same

                theoretically

(yes, it was incorrect before this change.)

> + * piece of memory is used for multiple purpose between different devices.
>    *
>    * @dmabuf: [in]     dmabuf buffer that will be renamed.
>    * @buf:    [in]     A piece of userspace memory that contains the name of
> @@ -346,19 +344,11 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
>   	if (IS_ERR(name))
>   		return PTR_ERR(name);
>   
> -	dma_resv_lock(dmabuf->resv, NULL);
> -	if (!list_empty(&dmabuf->attachments)) {
> -		ret = -EBUSY;
> -		kfree(name);
> -		goto out_unlock;
> -	}
>   	spin_lock(&dmabuf->name_lock);
>   	kfree(dmabuf->name);
>   	dmabuf->name = name;
>   	spin_unlock(&dmabuf->name_lock);
>   
> -out_unlock:
> -	dma_resv_unlock(dmabuf->resv);
>   	return ret;
>   }
>   
> 


-- 
~Randy