i have now implemented unix domain sockets to share the file descriptors of the buffer_handle_t but for some reason gralloc->lock does not want to work in the renderer app on the transfered buffer handle, any ideas?
(testing on my jolla phone with a small test application which creates a buffer and sends the handle to the sfdroid application

EDIT: after reviewing the comments in the android source i noticed that i missed a call to gralloc->registerBuffer. sharing the buffer handle works now