wlr-export-dmabuf synchronization
The current wlr-export-dmabuf protocol (and its wlr implementation) has a data race since the client doesn't tell the compositor when it's done with the dmabuf. Fixing this in wlr would at least require to extend the output interface to allow signaling it when an exported dmabuf can be used for rendering again. The protocol specification should first clarify though that frame.destroy means that the client has finished reading from all received dmabufs (or add a new request? @atomnuker). Apparently related to #1247, some things will change anyways when that is implemented.