the callback returns 0 to indicate that the buffer switch should not
occur yet, i.e. until the consumer has had a chance to read the
current set of ready sub-buffers. For the relay_buf_full() function
-to make sense, the consumer is reponsible for notifying the relay
+to make sense, the consumer is responsible for notifying the relay
interface when sub-buffers have been consumed via
relay_subbufs_consumed(). Any subsequent attempts to write into the
buffer will again invoke the subbuf_start() callback with the same