4.2 Unibus RL02 driver doesn't configure an off-line drive

[mogul at Su-Coyote.ARPA]

From:  Jeff Mogul <mogul at Su-Coyote.ARPA>

Description:
	If your system includes an RL02 drive (not that they are
	all that useful) but the drive is not loaded when the system
	is booted, the configuration procedure does not recogniz the
	drive and it cannot be used until the system is rebooted.
	
	Since the RL02 is a removable pack, and a darn small one at
	that, it's unpleasant to have to have a pack loaded whenever
	you boot the machine.
	
	The problem is that the distributed RL02 driver checks for
	a ready-to-use, loaded pack instead of simply checking that
	the drive is there.  This is probably being done because
	(as a comment in the code notes) the "Get Status" operation
	may return invalid data.  Presumably, the author felt that if
	the status is "all set to use", then it's valid.
	
Repeat-By:
	(You need a system with an RL02 that is NOT the root drive).
	Unload the RL02, reboot your system.
	Once it is running, load the RL02.  You won't be able to
	use it for anything.
Fix:
	The fix involves (1) assuming that after 8 tries, either the
	returned status is valid or if it isn't, we'll find out later
	anyway; (2) checking not for "Drive Error" (which is not set
	for either an off-line or a non-existant drive) but for "Composite
	Error", i.e., any error at all.
	
*** rl.c.old	Fri Jul 29 07:33:38 1983
--- rl.c	Mon Mar 26 18:13:05 1984
***************
*** 141,146
  	} while ((rladdr->rlmp.getstat&RLMP_STATUS) != RLMP_STATOK && ++ctr<8);
  	if ((rladdr->rlcs & RL_DE) || (ctr >= 8))
  		return (0);
  	if ((rladdr->rlmp.getstat & RLMP_DT) == 0 ) {
  		printf("rl%d: rl01's not supported\n", ui->ui_slave);
  		return(0);

--- 147,165 -----
  #ifdef	MUST_BE_ONLINE
  	if ((rladdr->rlcs & RL_DE) || (ctr >= 8))
  		return (0);
+ #else
+ 	/*
+ 	 * This code does NOT assume that the disk must be online
+ 	 * when the system boots.
+ 	 * 
+ 	 * We ignore the rlmp.getstat value; it only tells us if the pack
+ 	 * is loaded and online.  rlcs will show an OPI error if the drive
+ 	 * doesn't exist.  If an invalid status is returned on the eighth
+ 	 * try, we're erring on the side of optimism.
+ 	 */
+ 	if (rladdr->rlcs & RL_ERR)
+ 		return (0);
+ #endif	MUST_BE_ONLINE
  	if ((rladdr->rlmp.getstat & RLMP_DT) == 0 ) {
  		printf("rl%d: rl01's not supported\n", ui->ui_slave);
  		return(0);