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Subject: Re: [PATCH] dma-buf: support users to change dma_buf.name
To:     guangming.cao@mediatek.com, Sumit Semwal <sumit.semwal@linaro.org>,
        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, caoguangming34@gmail.com
References: <20210714122954.71931-1-guangming.cao@mediatek.com>
From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
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Am 14.07.21 um 14:29 schrieb guangming.cao@mediatek.com:
> From: Guangming Cao <Guangming.Cao@mediatek.com>
>
> User space user can call DMA_BUF_SET_NAME to set dma_buf.name,
> also add a kernel api for users to do same thing at kernel side.

Well if you want to add a kernel API to set the name you also need to 
provide an user for this.

Christian.

>
> Signed-off-by: Guangming Cao <Guangming.Cao@mediatek.com>
> ---
>   drivers/dma-buf/dma-buf.c | 28 ++++++++++++++++++++++------
>   include/linux/dma-buf.h   |  1 +
>   2 files changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 511fe0d217a0..949af232c644 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -331,20 +331,20 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
>    * purpose between different devices.
>    *
>    * @dmabuf: [in]     dmabuf buffer that will be renamed.
> - * @buf:    [in]     A piece of userspace memory that contains the name of
> + * @buf:    [in]     A piece of memory that contains the name of
>    *                   the dma-buf.
>    *
>    * Returns 0 on success. If the dma-buf buffer is already attached to
>    * devices, return -EBUSY.
>    *
>    */
> -static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
> +long dma_buf_set_name(struct dma_buf *dmabuf, const char *buf)
>   {
> -	char *name = strndup_user(buf, DMA_BUF_NAME_LEN);
> +	char *name = kstrndup(buf, DMA_BUF_NAME_LEN, GFP_KERNEL);
>   	long ret = 0;
>   
> -	if (IS_ERR(name))
> -		return PTR_ERR(name);
> +	if (!name)
> +		return -ENOMEM;
>   
>   	dma_resv_lock(dmabuf->resv, NULL);
>   	if (!list_empty(&dmabuf->attachments)) {
> @@ -361,6 +361,22 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
>   	dma_resv_unlock(dmabuf->resv);
>   	return ret;
>   }
> +EXPORT_SYMBOL_GPL(dma_buf_set_name);
> +
> +static long
> +dma_buf_set_name_user(struct dma_buf *dmabuf, const char __user *buf)
> +{
> +	char *name = strndup_user(buf, DMA_BUF_NAME_LEN);
> +	long ret = 0;
> +
> +	if (IS_ERR(name))
> +		return PTR_ERR(name);
> +
> +	ret = dma_buf_set_name(dmabuf, name);
> +	kfree(name);
> +
> +	return ret;
> +}
>   
>   static long dma_buf_ioctl(struct file *file,
>   			  unsigned int cmd, unsigned long arg)
> @@ -403,7 +419,7 @@ static long dma_buf_ioctl(struct file *file,
>   
>   	case DMA_BUF_SET_NAME_A:
>   	case DMA_BUF_SET_NAME_B:
> -		return dma_buf_set_name(dmabuf, (const char __user *)arg);
> +		return dma_buf_set_name_user(dmabuf, (const char __user *)arg);
>   
>   	default:
>   		return -ENOTTY;
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index efdc56b9d95f..e6612ab59a59 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -507,4 +507,5 @@ int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *,
>   		 unsigned long);
>   int dma_buf_vmap(struct dma_buf *dmabuf, struct dma_buf_map *map);
>   void dma_buf_vunmap(struct dma_buf *dmabuf, struct dma_buf_map *map);
> +long dma_buf_set_name(struct dma_buf *dmabuf, const char *name);
>   #endif /* __DMA_BUF_H__ */