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

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Message-ID: <20211026115248.9564-1-guangming.cao@mediatek.com>
Date:   Tue, 26 Oct 2021 19:52:48 +0800
From:   <guangming.cao@...iatek.com>
To:     <christian.koenig@....com>
CC:     <dri-devel@...ts.freedesktop.org>, <guangming.cao@...iatek.com>,
        <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>, <sumit.semwal@...aro.org>,
        <wsd_upstream@...iatek.com>,
        Guangming Cao <Guangming.Cao@...iatek.com>
Subject: Re: [PATCH v3] dma-buf: remove restriction of IOCTL:DMA_BUF_SET_NAME

From: Guangming Cao <Guangming.Cao@...iatek.com>

On Tue, 2021-10-26 at 13:18 +0200, Christian König wrote:
> 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>
>

So, here is no need to check return value of 'strndup_user',
just return without error code if the almost impossible error occurs?

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,
> 
>