+ *
+ * 1. A tape drive is a unique-open device; we refuse opens when it is already.
+ * 2. We keep track of the current position on a block tape and seek
+ * before operations by forward/back spacing if necessary.
+ * 3. We remember if the last operation was a write on a tape, so if a tape
+ * is open read write and the last thing done is a write we can
+ * write a standard end of tape mark (two eofs).
+ * 4. We remember the status registers after the last command, using
+ * then internally and returning them to the SENSE ioctl.
+ * 5. We remember the last density the tape was used at. If it is
+ * not a BOT when we start using it and we are writing, we don't
+ * let the density be changed.