The datab structure describes the data of a STREAMS message. The actual data contained in a STREAMS message is stored in a data buffer pointed to by
this structure. A msgb (message block) structure includes a field that points to a datab structure.
Because a data block can have more than one message block pointing to it at one time, the db_ref member keeps track of a data block's references, preventing it from being deallocated until all message blocks are finished with it.
unsigned char *db_base; /* first byte of buffer */
unsigned char *db_lim; /* last byte (+1) of buffer */
dbref_t db_ref; /* # of message pointers to this data */
unsigned char db_type; /* message type */
