Hello Guangming, Christian,
On Tue, 12 Oct 2021, 14:09 , <guangming....@mediatek.com> wrote: > From: Guangming Cao <guangming....@mediatek.com> > > > Am 09.10.21 um 07:55 schrieb guangming....@mediatek.com: > > From: Guangming Cao <guangming....@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 be waiting > for > > > IOCTL:DMA_BUF_SET_NAME rather than mmap. > > > > Sounds valid to me, but I have no idea why this restriction was added in > > the first place. > > > > Can you double check the git history and maybe identify when that was > > added? Mentioning this change in the commit message then might make > > things a bit easier to understand. > > > > Thanks, > > Christian. > It was add in this patch: https://patchwork.freedesktop.org/patch/310349/. > However, there is no illustration about it. > I guess it wants users to set_name when no attachments on the dmabuf, > for case with attachments, we can find owner by device in attachments. > But just I said in commit message, this is might not a good idea. > > Do you have any idea? > 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, and any accounting should probably use that, without relying on the name as much. So I don't have an objection to this change. Best, Sumit. > > > > > > > > Signed-off-by: Guangming Cao <guangming....@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..db2f4efdec32 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 theoretically 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 > > > @@ -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; > > > } > > > >
