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Subject: Re: [PATCH v3] dma-buf: remove restriction of IOCTL:DMA_BUF_SET_NAME
To:     guangming.cao@mediatek.com
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        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
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References: <0e062f12-7e79-5a05-1e7b-10dda8e353b7@amd.com>
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From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
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Date:   Thu, 28 Oct 2021 13:35:20 +0200
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Am 26.10.21 um 13:52 schrieb guangming.cao@mediatek.com:
> From: Guangming Cao <Guangming.Cao@mediatek.com>
>
> On Tue, 2021-10-26 at 13:18 +0200, Christian König wrote:
>> Am 14.10.21 um 12:25 schrieb guangming.cao@mediatek.com:
>>> From: Guangming Cao <Guangming.Cao@mediatek.com>
>>>
>>> In this patch(https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatchwork.freedesktop.org%2Fpatch%2F310349&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C6652f423b96547b8321308d998772121%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637708459727236977%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=4EFg60sCxQzNuMKB0VjhbpvoeGlcAbofErMtcjPtIfw%3D&amp;reserved=0),
>>> 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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatchwork.freedesktop.org%2Fpatch%2F310387%2F&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C6652f423b96547b8321308d998772121%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637708459727236977%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=c%2Bbso%2BSxiPjwlv%2B9tAzA4x0gf5UktREhSiAsODFkihk%3D&amp;reserved=0), 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@mediatek.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@amd.com>
>>
> So, here is no need to check return value of 'strndup_user',
> just return without error code if the almost impossible error occurs?

Good point, totally missed that one.

In that case I'm going to push the patch to drm-misc-next as is.

Regards,
Christian.

>
> Guangming.
>
>> 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,
>>