I'm working on getting the Venus driver to work inside QEMU guests, but when I
tested `vkcube` in a Linux guest with `VN_DEBUG=init`, I got `stuck in ring
seqno wait with iter at {i}` with updating i at exponentially increasing
intervals. Taking a cursor glance at the code, it seems that this is due to:
the cs encoder's buffer list being empty, or the buffers having a reported size
of 0. Is this a potential bug in venus, or is there something I have to
implement on the QEMU side? The version of venus I'm testing is 23.0.2.
