* description. That is, the lowest master that can be allocated to software
* writers is @sw_start and data from this writer will appear is @sw_start
* master in the STP stream.
+ *
+ * The @packet callback should adhere to the following rules:
+ * 1) it must return the number of bytes it consumed from the payload;
+ * 2) therefore, if it sent a packet that does not have payload (like FLAG),
+ * it must return zero;
+ * 3) if it does not support the requested packet type/flag combination,
+ * it must return -ENOTSUPP.
+ *
+ * The @unlink callback is called when there are no more active writers so
+ * that the master/channel can be quiesced.
*/
struct stm_data {
const char *name;