Hello Guangming, Christian,
On Tue, 12 Oct 2021, 14:09 , guangming.cao@mediatek.com wrote:
From: Guangming Cao Guangming.Cao@mediatek.com
Am 09.10.21 um 07:55 schrieb guangming.cao@mediatek.com: From: Guangming Cao Guangming.Cao@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.Cao@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; }