Anyone else but me that feels such a function could be useful?

My main use-case is that it would resolve the mutual refcounting problem:

1) drm buffer object caches a dma_buf pointer which it refcounts 2) The dma-buf holds a refcount to the buffer.

This is resolved today by having the user-space visible part of the drm-buffer holding the refcount to the dma_buf. When user-space closes the drm-buffer, the reference goes away, and eventually the buffer is freed, when all external dma-buf users are done with the dma-buf

However, this also means that the dma-buf remains for the buffer lifetime even when there are no external users, which bugs me a bit.

This can be resolved by viewing the drm buffer as a lookup structure that doesn't hold a refcount to the dma-buf, but that means that the lookup structure (buffer) would need to share locks with the dma-buf implementation, unless we have a get_dma_buf_unless_zero, which means we can use locks local to the lookup structure, the drm buffer. (See the last part of the kref documentation for a detailed discussion of this).

Now I don't think keeping the dma_buf for the drm buffer lifetime is a HUGE problem, but I just wanted to get people's views of this.

Thanks, Thomas