linux-kernel - Re: [PATCH v3] dma-buf: remove restriction of IOCTL:DMA_BUF_SET

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Message-ID: <0e062f12-7e79-5a05-1e7b-10dda8e353b7@amd.com>
Date:   Tue, 26 Oct 2021 13:18:53 +0200
From:   Christian König <christian.koenig@....com>
To:     guangming.cao@...iatek.com, sumit.semwal@...aro.org
Cc:     dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        matthias.bgg@...il.com, rdunlap@...radead.org,
        wsd_upstream@...iatek.com
Subject: Re: [PATCH v3] dma-buf: remove restriction of IOCTL:DMA_BUF_SET_NAME

Am 14.10.21 um 12:25 schrieb guangming.cao@...iatek.com:
> From: Guangming Cao <Guangming.Cao@...iatek.com>
>
> In this patch(https://patchwork.freedesktop.org/patch/310349),
> it add a new IOCTL to support dma-buf user to set debug name.
>
> But it also added a limitation of this IOCTL, it needs the
> attachments of dmabuf should be empty, otherwise it will fail.
>
> For the original series, the idea was that allowing name change
> mid-use could confuse the users about the dma-buf.
> However, the rest of the series also makes sure each dma-buf have a unique
> inode(https://patchwork.freedesktop.org/patch/310387/), and any accounting
> should probably use that, without relying on the name as much.
>
> So, removing this restriction will let dma-buf userspace users to use it
> more comfortably and without any side effect.
>
> Signed-off-by: Guangming Cao <Guangming.Cao@...iatek.com>

We could now cleanup the return value from dma_buf_set_name() into a 
void since that function can't fail any more as far as I can see.

But that isn't mandatory I think, patch is Reviewed-by: Christian König 
<christian.koenig@....com>

Regards,
Christian.

> ---
>   drivers/dma-buf/dma-buf.c | 17 +++--------------
>   1 file changed, 3 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 511fe0d217a0..5fbb3a2068a3 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 support changing the name of the dma-buf if the same
> + * 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
> @@ -341,25 +339,16 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
>   static long dma_buf_set_name(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);
>   
> -	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;
> +	return 0;
>   }
>   
>   static long dma_buf_ioctl(struct file *file,