.TITLE	FDHostTIMG - VAX/VMS VIRT DISK Host Process (image backup on tape)
	.IDENT	'V01-001c'
; Copyright 1991 Glenn C. Everhart
; all rights reserved
;
; FACILITY:
; 
; Host process for FD: unit that uses physical backed up image
; of a disk and treats it as if it were a disk. Device type
; or geometry must be specified, and the utility can either
; do its' access to a VMS Backup image of the disk, or to
; a straight dump of a disk, and can be told to skip files
; so that handling the Nth saveset on a tape is possible.
;
; Command format:
; FDHost/switches FDn: filespec
;
; FDHOST/CLEAR will zero the ref. count only...nothing more.
; Note deassign normally will NOT be via command (I don't see how a
; command could ever be read) but via exit AST. We could in principle arrange
; an I/O that fddrv would store somewhere, so that if this process exited the
; fddrv driver would be informed of it and could complete the I/O AND set
; itself offline, but I am uncomfortable with this kind of jiggery-pokery.
; Better to just let the ref count be zeroed, since that's the only "dirty" trace
; around. This may allow playing some games later with multiple hosts also.
;   The expectation is that an fd: unit being assigned will have FDHOST/CLEAR
; run on the FD: unit before assigning it if the unit was set incorrectly.
;
; Note: define VMS$V5 to build for Version 5.x of VMS.
;
vms$v5=0
; 
; AUTHOR:
; 
; G. EVERHART
; 11/17/1991 - Initial coding
; Notes: 100 block cache; see cachecnt parameter
; Initially no support for CRC or xor block checking (apart from
; skipping XOR blocks)
; Use crude factor 1.1 to adjust distances to blocks for xor
; blocks. This is the default and since we adjust position
; anyway it will not affect correct operation...only speed, and
; that not a whole lot.
;
; Revised to allow /cache:n switch to specify from 1 to 1000
; tape blocks. CRC checking "pencilled" in.
;--
	.PAGE
	.SBTTL	EXTERNAL AND LOCAL DEFINITIONS

	.LIBRARY /SYS$SHARE:LIB/
; 
; EXTERNAL SYMBOLS
; 

	$ADPDEF				;DEFINE ADAPTER CONTROL BLOCK
	$CRBDEF				;DEFINE CHANNEL REQUEST BLOCK
	$DCDEF				;DEFINE DEVICE CLASS
	$DDBDEF				;DEFINE DEVICE DATA BLOCK
	$DEVDEF				;DEFINE DEVICE CHARACTERISTICS
	$DPTDEF				;DEFINE DRIVER PROLOGUE TABLE
	$EMBDEF				;DEFINE ERROR MESSAGE BUFFER
	$IDBDEF				;DEFINE INTERRUPT DATA BLOCK
	$IODEF				;DEFINE I/O FUNCTION CODES
	$IRPDEF				;DEFINE I/O REQUEST PACKET
	$PRDEF				;DEFINE PROCESSOR REGISTERS
	$PCBDEF				;DEFINE PCB OFFSETS
	$SCSDEF
	$SBDEF
	$STSDEF
	$STSDEF		; Symbols for returned status.
	$DVIDEF		; Symbols for $GETDVI service.
	$DCDEF		; Symbols for device type.
	$SSDEF				;DEFINE SYSTEM STATUS CODES
	$UCBDEF				;DEFINE UNIT CONTROL BLOCK
	$VECDEF				;DEFINE INTERRUPT VECTOR BLOCK

; 
; No need for direct UCB access here; this is done via the driver
; itself. We just worry about the files, etc.
; 

	$FIBDEF			; Symbols for file information block.
	$IODEF			; Symbols for QIO functions.
	$DVIDEF			; Symbols for $GETDVI calls.
	$TPADEF			; Symbols for LIB$TPARSE calls.
; Macro to check return status of system calls.
;
	.MACRO	ON_ERR	THERE,?HERE
	BLBS	R0,HERE
	BRW	THERE
HERE:	.ENDM	ON_ERR
; definitions of offsets into vms backup savesets
bbh$w_size=0
bbh$w_opsys=2
bbh$w_subsys=4
bbh$w_applic=6	;1 => normal, 2 => xor block
bbh$l_number=8
;spares 20 bytes
bbh$w_structlev=32
bbh$w_volnum=34
bbh$l_crc=36
bbh$l_blocksize=40	; size of blocks in saveset (not data size; data+hdrs)
bbh$l_flags=44
; ignore the rest for now
brh$w_rsize=0	;record size
brh$w_rtype=2	;0=null, 1=summary, 2=volume, 3=file, 4=vbn, 5=physvol, 6=lbn, 7=fid
brh$l_flags=4
brh$l_address=8	;holds start lbn for lbn records
brh$l_spare=12
; data begins at offset 16 for rsize bytes
; block hdr length is exact. Add 16 to rec hdr length to get to next record.
; ignore the rest.
	.PSECT	FDHostD_DATA,RD,WRT,NOEXE,LONG

; Device geometry
; Use this table for "large" devices so that container files of
; sizes matching known geometry devices are made to appear to
; have exactly the known geometry. This will avoid a LOT of special
; case testing and allow insertion of more device geometries as we
; like
	.macro	Geotbl blks,cyl,trk,sect,id
	.irpc x,<id>
	.ascii /x/
	.endr
	.long	blks	;Number of blks on device
	.word	cyl	;number cylinders
	.byte	trk	;number tracks/cyl
	.byte	sect	;number sectors/track
	.endm
; Geoms MUST be in increasing order of size.
Geoms:
;		blks	cyl	trk	sect	id
	Geotbl  800,	1,	80,	10,	RX50
	Geotbl	4800,	200,	2,	12,	RK05
	Geotbl	10240,	256,	2,	40,	RL01 ;(sect=256 bytes)
	Geotbl	20480,	512,	2,	40,	RL02 ;(Sect=256 bytes)
	Geotbl	27126,	411,	3,	22,	RK06
	GeoTbl	53790,	815,	3,	22,	RK07
	GeoTbl	131680,	823,	5,	32,	RM03
	GeoTbl	138672,	1024,	8,	17,	RD53
	GeoTbl	171798,	411,	19,	22,	RP04
	GeoTbl	242606,	559,	14,	31,	RM80 ; (or RB80)
	GeoTbl	340670,	815,	19,	22,	RP06
	GeoTbl	500384,	823,	19,	32,	RM05
	GeoTbl	891072,	1248,	14,	51,	RA81
	GeoTbl	1008000,630,	32,	50,	RP07
	GeoTbl	1216665,1423,	15,	57,	RA82
	.Long	0,0,0,0,0		;list terminator
dvl:	.long	0
DESBLK:
	.LONG	0
	.ADDRESS	XITHDL		;EXIT HANDLER ADDRESS
	.long	0
	.address	dvl
	.LONG	0,0			;REST OF EXIT HANDLER CONTROL BLK
;
DEFAULT_DEVICE:
	.ASCID	/SYS$DISK/

	$ATRDEF
	$FABDEF
	$FATDEF
	$FIBDEF
	$IODEF
	$NAMDEF
	$RMSDEF
	$XABDEF
	.ALIGN LONG
DFAB_BLK: $FAB FNM=<FD0.DSK>,XAB=FNXAB,FAC=<BIO,get,put>,rfm=fix,DNM=<FDCONT.DSK>,mrs=512
DRAB_BLK: $RAB FAB=DFAB_BLK,BKT=0,RBF=RECBUF,UBF=RECBUF,USZ=512
	.align	long
RECBUF:	.BLKL	128	;512 BYTES = 128 LONGS
	.long	0,0	;safety
;
FNXAB:	$XABFHC	; XAB STUFF TO GET LBN, SIZE
	.BLKL	20 ;SAFETY
	.ALIGN LONG
IOSTATUS: .BLKQ 1

VDV_BUF:			; Buffer to hold device name for FD unit.
	.BLKB	40
VDV_BUF_SIZ = . - VDV_BUF

VDV_BUF_DESC:			; Descriptor pointing to VDVice name.
	.LONG	 VDV_BUF_SIZ
	.ADDRESS VDV_BUF

VPID:				; Owner of VDVice (if any).
	.BLKL	1

VDV_ITEM_LIST:			; VDVice list for $GETDVI.
	.WORD	 VDV_BUF_SIZ	; Make sure we a have a physical device name.
	.WORD	 DVI$_DEVNAM
	.ADDRESS VDV_BUF
	.ADDRESS VDV_BUF_DESC
	.WORD	 4		; See if someone has this device allocated.
	.WORD	 DVI$_PID
	.ADDRESS VPID
	.LONG	 0
	.WORD	 4
	.WORD	 DVI$_DEVCLASS	; Check for a terminal.
	.ADDRESS VDV_CLASS
	.LONG	 0
	.LONG	 0		; End if item list.

VDV_CLASS:
	.LONG	1

mbx_BUF:			; Buffer to hold mbxice name.
	.BLKB	40
mbx_BUF_SIZ = . - mbx_BUF

mbx_BUF_DESC:			; Descriptor pointing to mbxice name.
	.LONG	 mbx_BUF_SIZ
	.ADDRESS mbx_BUF

mPID:				; Owner of mbxice (if any).
	.BLKL	1

mbx_ITEM_LIST:			; mbxice list for $GETDVI.
	.WORD	 mbx_BUF_SIZ	; Make sure we a have a physical device name.
	.WORD	 DVI$_DEVNAM
	.ADDRESS mbx_BUF
	.ADDRESS mbx_BUF_DESC
	.WORD	 4		; See if someone has this device allocated.
	.WORD	 DVI$_PID
	.ADDRESS mPID
	.LONG	 0
	.WORD	 4
	.WORD	 DVI$_DEVCLASS	; Check for a terminal.
	.ADDRESS mbx_CLASS
	.LONG	 0
	.LONG	 0		; End if item list.

mbx_CLASS:
	.LONG	1

DEFNAM:

WRK:	.BLKL	4	;SCRATCH INTEGER
; descriptor string for getting numeric values read in
wrkstr:	.word	20	;length 
	.byte	dsc$k_dtype_t	;text
	.byte	1	;static
	.address	wrkdat
wrkdat:	.blkb	20
	.byte	0,0,0,0	;safety
; DESCRIPTOR FOR VDn: "FILENAME"
	.ALIGN LONG
VDFNM:	.WORD	 255.	;LENGTH
VDFTP:	.BYTE	DSC$K_DTYPE_T	;TEXT TYPE
	.BYTE	1	; STATIC STRING
	.ADDRESS	VDFNMD
VDFNMD:	.BLKB	256.	; DATA AREA
;
VDCHN:	.LONG	0	;CHANNEL HOLDERS
;
MBCHN:	.long	0	; channel for mailbox used to communicate with fddrv
MBUCB:	.long	0	; UCB address for mailbox
weakflg: .long	0	;1 if "weak" mode used
crcfg:	.long	0	;flag that crc is in use
xrg11:	.long	0	;counter for entries to xor block getgrp
rg11:	.long	0	;retry counter
joggle:	.long	0
icrcfg:	.long	0	;neg=ignore crc; 0=normal; pos=force crc use
ixorfg:	.long	0	;ignore xor flag, ignore if nonzero
cacds:	.ascid	/CACHE/	; use eventually for cache:n spec
icrcds:	.ascid	/IGNCRC/	;ignore CRC flag
fcrcds:	.ascid	/FRCCRC/	;force CRC flag
igxords: .ascid	/IGNXOR/	;ignore XOR groups if set
CLRDS:	.ASCID	/CLEAR/
BACDS:	.ASCID	/IMAGE/	;IMAG SWITCH, means not vms backup, just device image
SKIPds:	.ascid	/SKIP/	;SKIP NO. FILES BEFORE START
TYPDS:	.ASCID	/TYPE/	;DRIVE TYPE (FOR GEOMETRY)
TRKDS:	.ASCID	/TRK/	;TRACKS
CYLDS:	.ASCID	/CYL/
SECDS:	.ASCID	/SEC/
;ASDSC:	.ASCID	/ASSIGN/
fileds:	.ascid	/FILE/	;use if file, not tape
;DASDSC:	.ASCID	/DEASSIGN/
P1DSC:	.ASCID	/UNIT/
P2DSC:	.ASCID	/FNAM/
	.EVEN
; DESCRIPTOR FOR DVn:DSKFIL "FILENAME"
; (this will be a tape here most of the time)
	.ALIGN LONG
DDFNM:	.WORD	 255.	;LENGTH
DDFTP:	.BYTE	DSC$K_DTYPE_T	;TEXT TYPE
	.BYTE	1	; STATIC STRING
DDFNA:	.ADDRESS	DDFNMD
DDFNMD:	.BLKB	256.	; DATA AREA
DDCHN:	.LONG	0
;
;TYPE descriptor (GETS TEXT)
	.ALIGN LONG
TYPFNM:	.WORD	 255.	;LENGTH
KYFTP:	.BYTE	DSC$K_DTYPE_T	;TEXT TYPE
	.BYTE	1	; STATIC STRING
KYFNA:	.ADDRESS	TYPFNMD
TYPFNMD: .BLKB	256.	; DATA AREA
trks:	.long	0	;tracks/cyl
cyls:	.long	0	;cylinders
secs:	.long	0	;sectors/track
backfg:	.long	1	;backup mode flag
fsflg:	.long	0	;1 if file structured (i.e. using saveset file on disk)
skps:	.long	0	;files to skip
currec:	.long	0	;record on tape currently (in current file)
curlblk: .long	0	; lo blk in current record
opcnt:	.long	0	;count of operations (for LRU stuff)
xoradr:	.long	0	;start of xor area
xorsiz:	.long	0	;xor grp size
xormx=22
xseq1:	.long	0
xbadcrc: .long	0,0
xcnt:	.long	0
cachecntmx=1000+xormx
cachecnt: .long	100	;cache size (must be 1 or more)
; store cache tape offsets here with the format
;	tape-record	start LBN of data contained  end LBN	op count of last use
	.align long
cacheidx:
	.rept	cachecntmx
	.long	0,0,0,0
	.endr

;
;
; Data area for "disk"
;
	.align long
; This is needed for the first block read-in, since prior to that we don't
;know the block size on the tape. Once we get things started, we extend
;the region and start using the cache as buffers for our data directly.
fd_longs=16384		; maximal sized tape blk
fd_data::
	.BLKL fd_longs
	.blkl	128	;guard area for safety during debug...
fd_tbf:	.long	1	;block factor for tape blks in 512 byte units
fd_siz:	.long	0	;actual size of blks
; ucb data area
HSTUCB:	.LONG	0	;HOST UCB ADDRESS
;OURPID:	.LONG	0	;PID OF THIS PROCESS
iosb:	.long	0,0,0,0	;iosb
ioprog:	.long	0	; i/o in progress flag if nonzero
; BUFFER FOR COPIES OF DRIVR DATA
BUFHDR:	.LONG	0,0,0,0,0
BUF:	.BLKL	8192.	; DATA AREA
	.LONG	0,0	;SAFETY BUFFERS
SETFD:	.LONG	0	;DECLARE PROCESS
	.LONG	0	;PID
HSTFZ:	.LONG	1	;DISK SIZE
	.LONG	0,0,0,0	;EXTRA STUFF FOR OTHER CALLS
SETFDL=.-SETFD
	.LONG	0,0,0,0,0	;SAFETY
HSTFSZ:	.LONG	0	;DISK SIZE
vmsiz:	.long	0	; # bytes for memory area
vmloadr: .long	0	; low address
vmhiadr: .long	0	; high address
vmblks:	.long	0	; # blks in region
;
	.PSECT	FDHostD_CODE,RD,WRT,EXE,LONG
	.ENTRY	FDHostD,^M<R2,R3,R4,R5,R6,R7,R8,R9,R10,R11>
; only fdn: name on command line
	clrl	curlblk
	clrl	currec
	clrl	skps
	PUSHAB	WRK		;PUSH LONGWORD ADDR FOR RETLENGTH
	PUSHAB	VDFNM		;ADDRESS OF DESCRIPTOR TO RETURN
	PUSHAB	P1DSC		; GET P1 (VDn: UNIT)
	CALLS	#3,G^CLI$GET_VALUE	;GET VALUE OF NAME TO VDFNM
	ON_ERR	FDHostD_EXIT
290$:
	clrl	clrcnt	;flag clear count if 1
	PUSHAB	clrds	; 'CLEAR'
	CALLS	#1,G^CLI$PRESENT	; IS /CLEAR USED?
	CMPL	R0,#CLI$_PRESENT	; IF EQ YES
	BNEQ	293$
	incl	clrcnt			; FLAG CLEARING USAGE
	BRW	295$			;ON CLEAR DON'T BOTHER WITH 2ND FILENAME
293$:
	PUSHAB	WRK		; GET 2ND FILE (REAL FILE) LONGWORD FOR LEN
	PUSHAB	DDFNM		; & ITS DESCRIPTOR
	PUSHAB	P2DSC		; & PARAMETER NAME 'P2'
	CALLS	#3,G^CLI$GET_VALUE	; GET FNM
	ON_ERR	fdhostd_EXIT
	clrl	fsflg		;say not file structured
;	pushab	fileds	;see if /file
;	calls	#1,g^cli$_present
;	cmpl	r0,$cli$_present	;there?
;	bneq	150$			;in neq no
;	incl	fsflg
;150$:
;	tstl	fsflg			;if not fs, get channel
;	bneq	151$
; Initial version has file structured operations commented out or simply not
; yet filled in. I want to get it working with tapes first and will deal
; with disk savesets later.
	$ASSIGN_S -				; Get a channel to the 
		DEVNAM=DDFNM,-		; device for host file
		CHAN=DDCHN
	ON_ERR	fdhostd_EXIT
;	brw	151$
;150$:
;; Don't open the file unless using file-structured access..otherwise we just use
;; logical QIOW$ calls.
;; OPEN THE FILE, CHECK ITS INITIAL LBN
;; IF ERROR OR NOT CONTIG, EXIT...
;; DO VIA OPENING FILE AND READING ITS' STATBLOCK VIA
;; QIO...
;; SET UP FOR FILENAME WE REALLY FOUND IN FAB...
;	MOVL	DDFNA,DFAB_BLK+FAB$L_FNA	;SET UP FILENAME ADDR
;	MOVB	DDFNM,DFAB_BLK+FAB$B_FNS	;AND LENGTH
;	brb	159$
;149$:	brw	fdhostd_exit
;159$:
;	$OPEN	FAB=DFAB_BLK
;	BLBC	R0,149$		; FAILURE IF FILE WON'T OPEN
;; FNXAB HAS INFO ON LBN, SIZE
;;	MOVL	FNXAB+XAB$L_SBN,HSTLBN	; GET HOST'S start LBN (0 IF NON CONTIG.)
;	MOVL	FNXAB+XAB$L_HBK,HSTFSZ	; GET FILE SIZE. (CHECK THAT BELOW)
;; No need to decrement size, but must make it a multiple of 64
;; blocks for a 64-sector geometry.
;;	DECL	HSTFSZ		;;;COUNT DOWN 1 TO ACCOUNT FOR BOOT BLOCK
;	BICL2	#63,HSTFSZ	;;;MAKE A MULTIPLE OF 64 BLKS
;	MOVL	HSTFSZ,HSTFZ		;FILE SIZE
;	$CONNECT	RAB=DRAB_BLK	;FINISH OPEN
;	BLBC	R0,149$		; FAILURE IF FILE WON'T OPEN
;151$:
; got channel or file to tape or pseudotape saveset. Now get geometry
	movl	#0,secs	;default geometry
	movl	#0,trks		;is 64/1/n
	movl	#0,cyls
; Use these zeroes to flag that nothing has been entered so we can
; fill in backup file's info unless something was given explicitly.
;try and parse /type:dvtp for known geometry.
	PUSHAB	typds	; 'type'
	CALLS	#1,G^CLI$PRESENT	; IS /type USED?
	CMPL	R0,#CLI$_PRESENT	; IF EQ YES
	bneq	295$			; if no /type given, ignore
	PUSHAB	WRK		; GET LONGWORD FOR LEN of type
	PUSHAB	TYPFNM		; & ITS DESCRIPTOR
	PUSHAB	TYPDS		; & PARAMETER NAME 'TYPE'
	CALLS	#3,G^CLI$GET_VALUE	; GET FNM
	ON_ERR	fdhostd_EXIT
; now kyfnmd should contain data of key string as text
	movl	wrk,typfnm	;store data length of returned string
	movab	geoms,r2	;get tbl offset
152$:	cmpl	(r2)+,typfnmd	;all types are 4 chars long
	beql	153$		;if eql got the geom.
	addl2	#8,r2		;else pass to next entry
	tstl	4(r2)		;got to end of tbl?
	bneq	152$		;no, try next
	brw	295$		;if no find, skip /type processing
153$:	tstl	(r2)+		;pass no. blks
	movzwl	(r2)+,cyls	;store cylinders
	movzbl	(r2)+,trks	;trks/cyl
	movzbl	(r2)+,secs	;and sect/trk
295$:
	movl	#1,backfg		;set backup at first
	pushab	bacds	;'imag' ; defaulted in .cld file is /imag switch
	calls	#1,g^cli$present	;did user say /back
	cmpl	r0,#cli$_present	;if neql no
	bneq	154$			; so branch if no /back seen
	clrl	backfg	;/image switch means no vms backup
154$:
	clrl	icrcfg		;default crc treatment
	pushab	icrcds		;see if /igncrc spec'd
	calls	#1,g^cli$present	;did user say so?
	cmpl	r0,#cli$_present	;if eql yes
	bneq	601$
	decl	icrcfg		;if ignore crc spec'd flag is <0
601$:
	pushab	fcrcds		;/frccrc spec'd?
	calls	#1,g^cli$present	;did user say so?
	cmpl	r0,#cli$_present	;if eql yes
	bneq	602$
	incl	icrcfg		;if force crc spec'd flag is >0
602$:
	clrl	ixorfg
	pushab	igxords		;/ignxor spec'd?
	calls	#1,g^cli$present	;did user say so?
	cmpl	r0,#cli$_present	;if eql yes
	bneq	603$
	incl	ixorfg		;if ignore xor spec'd flag is >0
603$:
;check if user specified separate geometry
	pushab	cylds		;user specify a number of cylinders?
	CALLS	#1,G^CLI$PRESENT
	CMPL	R0,#CLI$_PRESENT
	bneq	155$		;if neq no /cyl:nnnn given
;get no. cyls.
	pushab	wrk		;ret length longword
	pushab	wrkstr		;scratch string
	pushab	cylds		;get nnnn from /cyl switch
	calls	#3,g^cli$get_value	;get value of lbn
	on_err fdhostd_Exit	;skip on error
; string in wrkdat
	pushl	#17		;mask, ignore blanks
	pushl	#4		;4 bytes in result
	pushab	cyls		;where to store result
	pushab	wrkstr
	calls	#4,g^ots$cvt_tu_l	;convert text to binary
	on_err fdhostd_Exit
155$:
	movl	#100,cachecnt
	pushab	cacds		;/cache:n spec'd?
	calls	#1,g^cli$present
	cmpl	r0,#cli$_present
	bneq	256$		;if not spec'd leave at default
	pushab	wrk
	pushab	wrkstr
	pushab	cacds		;get the value
	calls	#3,g^cli$get_value	;get value of cache
	on_err fdhostd_Exit	;skip on error
;convert to binary
	pushl	#17		;mask, ignore blanks
	pushl	#4		;4 bytes in result
	pushab	cachecnt		;where to store result
	pushab	wrkstr
	calls	#4,g^ots$cvt_tu_l	;convert text to binary
	on_err fdhostd_Exit
	cmpl	cachecnt,#1	;ensure in limits
	bgtr	257$
	movl	#1,cachecnt	;must have one buffer anyway
257$:
	cmpl	cachecnt,#xormx	;if too small can't do xor stuff
	bgeq	1258$
	incl	ixorfg		;flag can't do xors
	clrl	xorsiz
1258$:
	cmpl	cachecnt,#<cachecntmx-xormx>	;over max?
	blss	258$
	movl	#<cachecntmx-xormx>,cachecnt	;if so clamp
258$:
256$:
	pushab	trkds		;user specify a number of cylinders?
	CALLS	#1,G^CLI$PRESENT
	CMPL	R0,#CLI$_PRESENT
	bneq	156$		;if neq no /trk:nnnn given
;get no. trks.
	pushab	wrk		;ret length longword
	pushab	wrkstr		;scratch string
	pushab	trkds		;get nnnn from /trk switch
	calls	#3,g^cli$get_value	;get value of lbn
	on_err fdhostd_Exit	;skip on error
; string in wrkdat
	pushl	#17		;mask, ignore blanks
	pushl	#4		;4 bytes in result
	pushab	trks		;where to store result
	pushab	wrkstr
	calls	#4,g^ots$cvt_tu_l	;convert text to binary
	on_err fdhostd_Exit
156$:
	pushab	secds		;user specify a number of cylinders?
	CALLS	#1,G^CLI$PRESENT
	CMPL	R0,#CLI$_PRESENT
	bneq	157$		;if neq no /sec:nnnn given
;get no. sectors.
	pushab	wrk		;ret length longword
	pushab	wrkstr		;scratch string
	pushab	secds		;get nnnn from /sec switch
	calls	#3,g^cli$get_value	;get value of lbn
	on_err fdhostd_Exit	;skip on error
; string in wrkdat
	pushl	#17		;mask, ignore blanks
	pushl	#4		;4 bytes in result
	pushab	secs		;where to store result
	pushab	wrkstr
	calls	#4,g^ots$cvt_tu_l	;convert text to binary
	on_err fdhostd_Exit
157$:
	pushab	skipds		;user specify skips?
	CALLS	#1,G^CLI$PRESENT
	CMPL	R0,#CLI$_PRESENT
	bneq	158$		;if neq no /skip:nnnn given
;get no. skips
	pushab	wrk		;ret length longword
	pushab	wrkstr		;scratch string
	pushab	skipds		;get nnnn from /skip switch
	calls	#3,g^cli$get_value	;get value of string
	on_err fdhostd_Exit	;skip on error
; string in wrkdat
	pushl	#17		;mask, ignore blanks
	pushl	#4		;4 bytes in result
	pushab	skps		;where to store result
	pushab	wrkstr
	calls	#4,g^ots$cvt_tu_l	;convert text to binary
	on_err fdhostd_Exit
158$:

; MUST HAVE ASSIGNMENT TO VD: UNIT IN ANY CASE.
	$ASSIGN_S -
		DEVNAM=VDFNM,-	; GET CHANNEL FOR VDn:
		CHAN=VDCHN
	ON_ERR	FDHostD_EXIT	; SKIP OUT IF ERROR
	$GETDVI_S -
		CHAN=vdchn,-	; Command line has device name.
		ITMLST=VDV_ITEM_LIST
	BLBS	R0,140$
	BRW	FDHostd_EXIT
140$:
	tstl	clrcnt
	beql	1162$
	brw	162$
1162$:
;	bneq	162$		;if just clearing ref count, no need for mbx
; Set up mailbox channel
	$crembx_s prmflg=#0,chan=mbchn,maxmsg=#576,bufquo=#5760,-
		promsk=#0
	On_ERR	fdhostd_exit
; need to get UCB address here somehow...
	$GETDVI_S -
		CHAN=mbchn,-	; Command line has device name.
		ITMLST=mbx_item_list
	BLBS	R0,176$
161$:	BRW	FDHostd_EXIT
176$:
; This is a good time to set up the tape unit since we want it set up
; already by the time we start.
	clrl	currec		;set record zero
	clrl	curlblk		;lo blk=0 too
	$qiow_s	chan=ddchn,func=#io$_rewind,iosb=iosb	;rewind the tape first
	tstl	skps		;skipping any files
	beql	230$		;if eql no, so don't bother messing with tape
; skip "skps" files on tape
	movl	skps,r6		;count filoes to skip
	tstl	backfg		;vms backup mode?
	beql	231$		;if eql no
	mull2	#3,r6		;if not, skip 3n files
231$:
	movl	r6,wrk+4
;	$qiow_s	#2,ddchn,#io$_skipfile,iosb,,,wrk+4,,,,,
	clrq	-(sp)
	clrq	-(sp)
	pushl	#0
	pushl	r6
	clrq	-(sp)
	pushab	iosb
	movzwl	#io$_skipfile,-(sp)
	movzwl	ddchn,-(sp)
	pushl	#2
	calls	#12,g^sys$qiow
	On_ERR	fdhostd_exit
	movl	iosb,r0
	On_ERR	fdhostd_exit
;skip r6 files
230$:
	tstl	backfg		;backup must skip 1 more
	beql	232$
	movl	#1,wrk
	clrq	-(sp)
	clrq	-(sp)
	pushl	#0	;homemade qio because VMS macro is DUMB!! (Dos-11 and RSX macros
	pushl	#1	;were much smarter! The VMS macro-32 language is okm but the
	clrq	-(sp)	;$qiow_s macro is not well written)
	pushab	iosb
	movzwl	#io$_skipfile,-(sp)
	movzwl	ddchn,-(sp)
	pushl	#2
	calls	#12,g^sys$qiow
;	$qiow_s	#2,ddchn,#io$_skipfile,iosb,,,#1,,,,,
;	$qiow_s	chan=ddchn,func=#io$_skipfile,iosb=iosb,p1=wrk
	On_ERR	fdhostd_exit
	movl	iosb,r0
	On_ERR	fdhostd_exit
232$:
; tape is now positioned at start of the file we desire.
;now get blocksize by reading a record of tape
;	movab	fd_data,r5
;	movl	r5,wrk+4
	$qiow_s	chan=ddchn,func=#io$_readlblk,iosb=iosb,p1=fd_data,p2=#65535
	On_ERR	fdhostd_exit
; check iosb, if ok, get real count
	blbs	iosb,235$	;if low bit on, looks ok
	brw	fdhostd_exit
235$:
	movzwl	iosb+2,r5	;r5=count xferred
	movl	r5,fd_siz	;store
	tstl	backfg		;vms backup mode should subtract block header slop
	beql	234$
	cmpl	bbh$l_blocksize+fd_data,r5	;use recorded block count
	beql	236$
;recorded byte count not the same as we observed by reading. Doesn't look like
; a saveset! Skip out now.
	brw	fdhostd_exit	;skip out
236$:
; check crc (when we get more time and info; Backup uses CRC16 and autodin
; polynomials (120001 octal and hex edb88320) but I don't have exact info
; on which and where...nevertheless I *HAVE* found out...
	movab	fd_data,r9	;pass data address for block
; we can't use crc unless we know crc exists in the data. however, perhaps
; it is valid to say if crc is ok in initial block, it exists in the saveset and can
;be used.
	jsb	crcck		;check crc error
	movl	r0,crcfg
	decl	crcfg		;crc flag nonzero if first blk crc was off
	tstl	icrcfg		;/igncrc or /frccrc flags set?
	beql	604$		;if not skip
	blss	605$		;if <0 then disable crc
;flag was >0
	clrl	crcfg		;assume first forcing CRC use
	brb	604$
605$:	movl	#1,crcfg	;disable crc use
604$:
;	on_error fdhostd_Exit	;skip out via r0 code if bad CRC
; Note we HAVE to be more tolerant of CRC errors once we get going and try
; to get data from further down the tape.
	subl2	#512,r5		;rough data size
234$:	ashl	#-9,r5,r5		;shift off cruft
	movl	r5,fd_tbf	;save as (approx) blocking factor
; then skip back a record
	movl	#-1,wrk
;	$qiow_s	#2,ddchn,#io$_skiprecord,#iosb,#-1,,,,,
	clrq	-(sp)
	clrq	-(sp)
	pushl	#0
	pushl	wrk	;pass rec cnt by ref
	clrq	-(sp)
	pushab	iosb
	movzwl	#io$_skiprecord,-(sp)
	movzwl	ddchn,-(sp)
	pushl	#2
	calls	#12,g^sys$qiow
	On_ERR	fdhostd_exit
	movl	iosb,r0
	On_ERR	fdhostd_exit
; Now set up our cache by allocating amount desired.
; For this go-round, let us assume we want to cache 100 tape blocks.
; Use method suitable for really large caches since lib$get_vm is limited
; to a few hundred pages and that often will NOT be sufficient.
	movl	fd_Siz,r4	;get size of tape blocks (so we can read to cache
				; area directly, saving zillions of movc3's.)
	addl2	#511,r4		;round up to a full block
	ashl	#-9,r4,r4	;make block count
; handle space for xor blocks
;;;
; Since we want to handle xor areas as the top of the cache area in one
; $expreg, we must find the xor factor sooner.
	pushl	r0
	pushl	r3
	pushl	r4
	tstl	backfg		;be very sure it's /backup mode
	beql	366$		;skip if not
	movab	fd_data,r3	;get to data area
	movzwl	(r3),r4		;get size of record
367$:	addl2	r4,r3		;get past block hdr
	movab	fd_Data,r0
	addl2	fd_siz,r0	;end of what was read
	cmpl	r3,r0	;past end of buffer?
	blss	365$		;if so just end
	brw	fdhostd_exit	; (serious error if no info; exit)
365$:	movzwl	(r3),r4		;get record size
	addl2	#16,r4		;pass hdr
	cmpw	brh$w_rtype(r3),#1	;summary record?
	bneq	1365$
	pushl	r3
	addl2	#16,r3
	jsb	getxor		;get xor factor
	popl	r3
	brb	366$		;then proceed
1365$:
	brb	367$		;else check next in buffer
366$:
	popl	r4
	popl	r3
	popl	r0
;;;
	clrl	r5
	tstl	backfg		;in backup mode?
	beql	1234$
	movl	xorsiz,r5	;number of xor blocks (use top of region for these if we must)
	beql	1234$
	cmpl	xorsiz,#xormx	;only handle 20 blk or less groups
	bleq	1233$
	clrl	r5		;zero our extra xor area count
	incl	ixorfg		;set no xor forced flag
	clrl	xorsiz		;flag we can't do xors
	brb	1234$
1233$:	mull2	fd_siz,r5	;make a mem size out of it
	ashl	#-9,r5,r5	;get blks for a moment
1234$:
; now r5 contains either 0 or # blks for xor area
;finish prep for expreg call now.
	mull2	cachecnt,r4	;multiply by number of such blocks in our cache
	addl2	r5,r4		;add in xor blk area if any
	movl	r4,r5		;store in r5 also for later test
	ashl	#9,r4,r4	;and turn it back into a byte count
	addl2	#1024,r4	;add a K for good luck
	movl	r4,vmsiz	;save size needed
;now use $expreg to get some space
	clrl	-(sp)	; region 0 (p0 space)
	clrl	-(sp)	;access mode (user)
	moval	vmloadr,-(sp)	;low/high address area
	movl	r5,-(sp)	;blocks to cover
	addl2	#2,(sp)		;+ a bit of slop
	calls	#4,g^sys$expreg	;get some space
	on_err fdhostd_exit	;just exit if we got an error allocating space
	subl3	vmloadr,vmhiadr,r0	;get address delta
	ashl	#-9,r0,r0	;make a block count
	cmpl	r0,r5		;enough?
	bgtr	233$		;if gtr, then all's well
	brw	fdhostd_exit	;else foo, skip out
233$:
	movl	vmhiadr,xoradr	;xor addr at high mem
	subl	#512,xoradr	;buffer blk
	movl	xorsiz,r0	;number of blks in xor group
;have to do this after fd_siz is filled in
	mull2	fd_siz,r0	;make a memory amount
	subl2	r0,xoradr	;and get start address
				;saving for later use.
;
;memory in cache now looks OK.  Since we use a separate table earlier as the
;index (cacheidx) which has taperec, data LBN start, and op-count (so we can deal
;with a LRU index) we don't need to mess with these data areas at all. The
;assembler init's the index for us.

; Got now the actual device name of the mailbox
; Let the kernel call perform the UCB lookup for us.
;
; FOUND A UNIT. NOW DECLARE EXIT HANDLER TO CLEAN UP
; IF WE GET A $FORCEX TO TERMINATE THE HOST PROCESS.
	PUSHAB	DESBLK		; ADDRESS OF DESBLK
	CALLS	#1,G^SYS$DCLEXH	; DECLARE EXIT HANDLER
; NOW GET OUR PID FOR USE LATER
;
162$:
	$CMKRNL_S -
		ROUTIN=BASHUCB,ARGLST=K_ARG
; Now we have the PID for our process in OURPID and are ready to tell
; the driver we're here!
	tstl	clrcnt
	beql	1161$
	brw	161$
1161$:
;	bneq	161$		;exit now if just zeroing count
; Note we must modified func code from io$_format to something with
; a modifier bit set so FDDRV will treat this as OUR special QIO.
; store geometry of disk
; NOTE: When we get a usable description of Backup format, the physical volume
;block contains the correct geometry for the saveset. This should be used as
; the default if no explicit geometry information is supplied.
; Examining some dumps shows the offsets from the start of the data area of
; they physical volume record are:
; sectors: byte 6
; tracks:  byte 11
; cyls:    word at 16
; blocks: longword at 22 off the start (i.e. after 16 byte header info)
; So let's do it...
	brb	170$
171$:	brw	fdhostd_exit	;major lossage if invalid geometry
170$:
	tstl	backfg		;/backup format?
	beql	164$		;if eql no, so no info is in data area
     	tstl	trks		;data given explicitly?
     	bneq	164$		;yes, no default
; if trks=0 then sectors and cylinders better also be zero or
; we have an invalid configuration.
;  It is possible, I suppose, to allow overrides of only one of these
; but most of the time such an override would just be a user mistake
; and it's better just to scram rather than produce an invalid or almost
; valid volume. Such a thing seems likely to screw up VMS...
	tstl	secs
	bneq	171$
	tstl	cyls
	bneq	171$
	movab	fd_data,r3	;get to data area
	movzwl	(r3),r4		;get size of record
167$:	addl2	r4,r3		;get past block hdr
	movab	fd_Data,r0
	addl2	#65535,r0
	cmpl	r3,r0	;past end of buffer?
	blss	165$		;if so just end
	brw	fdhostd_exit	; (serious error if no info; exit)
165$:	movzwl	(r3),r4		;get record size
	addl2	#16,r4		;pass hdr
	cmpw	brh$w_rtype(r3),#5	;physvol record?
	beql	166$		;if eql yes, get data
	cmpw	brh$w_rtype(r3),#1	;summary record?
	bneq	1165$
	pushl	r3
	addl2	#16,r3
	jsb	getxor		;get xor factor
	popl	r3
1165$:
	brb	167$		;else check next in buffer
166$:	addl2	#16,r3		;pass record hdr
; following offsets seen empirically
	movzbl	6(r3),secs	;store sectors
	movzbl	11(r3),trks	;and tracks
	movzwl	16(r3),cyls	;and cylinders
; Having better docs, get the geometry in a less fragile
; way. The offsets above are not guaranteed but getgeom's
; method IS guaranteed to be correct.
	jsb	getgeom		;get geometry correctly
164$:
; nowe compute device size
	movl	secs,r2		;get size of device now
	mull2	trks,r2		;sect*trks*cyls
	mull2	cyls,r2		;r2 now has blocks
	movl	r2,hstfz
	movl	r2,hstfsz	;store as device size
; note hstfz should equal 22(r3) if a backup set.
	MOVL	OURPID,SETFD+4	;STORE PID (IPID!!!)
	movl	HSTFSZ,setfd+8	;size of disk (preset also)
	movl	mbucb,setfd+12		; Comm mailbox UCB address
	CLRL	SETFD		; flag that this is the setup
	movl	#setfdl,r4	; length of buffer
	movl	trks,setfd+16	;let fddrv know our geometry
	movl	secs,setfd+20	;trks,sects, cyls
	movl	cyls,setfd+24
	$qiow_s chan=vdchn, -
	iosb=#iosb,func=#<io$_format+128>,p1=setfd,p2=R4
	ON_ERR	FDHostD_EXIT	; SKIP OUT IF ERROR
	clrl	ioprog		; no i/o in progress yet
; now we're ready to await work from the driver
	clrl	opcnt
EVTLOOP:
	incl	opcnt		;bump operation count
; When FDDRV has work, it sends the buffer header it has via a
; mailbox message. Read that here to get our indication there
; is something to do, and incidentally to get initial info on I/O
; direction and size.
;
; Read the mailbox to get our data
; Use QIOW$ to assure that we don't do anything until there is work.
; (this also avoids having to use internal routines to control
;  host execution.)
	$qiow_s efn=#10,chan=mbchn,-
	iosb=#iosb,func=#io$_readlblk,p1=bufhdr,p2=#20
	ON_ERR	FDHostD_EXIT	; SKIP OUT IF ERROR
;	$qiow_s efn=#1,chan=vdchn,func=#io$_format,p1=#setfd,p2=#setfdl
;SHOULD NOW HAVE HEADER...
; Check call is not spurious. Driver sets 255 in buffer header when it
; gets done an i/o for client, and puts 0 or 1 there for a real
; transfer.
	cmpl	bufhdr,#2
	bgtru	evtloop		;if not really doing i/o, spurious ef
				; set, just ignore
	MOVL	#1,IOPROG	;FLAG AN I/O IN PROGRESS THAT NEEDS TO
				;BE COMPLETED
	CMPL	BUFHDR,#1	;1=WRITE, SOMETHING'S WAITING IN THE DRIVER
	beql	writeop
	jmp	readop
;	BNEQ	READOP
; writing the virtual disk. In this case this won't actually do much of anything
; save throw the data away after grabbing it from the driver. There is NO
; intention here of supporting writing to a tape as though it were a disk,
; seeing that the hardware doesn't support such things.
WRITEOP:
; BUFHDR+8 CONTAINS BYTECOUNT FOR DATA PART OF TRANSFER
	MOVL	#20,SETFD+8	;BUFFER HEADER size
	ADDL2	BUFHDR+8,SETFD+8	;SO ADD HEADER SIZE
	MOVL	#3,SETFD	;GET DATA
	MOVAB	BUFHDR,SETFD+4	;BUFFER HDR ADDRESS
	movl	#ss$_nowrt,setfd+12	;wrtlock indicator
	movl	#setfdl,r4
; get the data via a transfer that completes in the FDT area of fddrv.
	$qiow_s efn=#1,chan=vdchn, -
	iosb=#iosb,func=#<io$_format+128>,p1=setfd,p2=R4
	ON_ERR	FDHostD_EXIT	; SKIP OUT IF ERROR
; then complete user's I/O transaction
; LOADS DATA INTO LOCAL BUFFER FROM DRIVER
	MOVL	#1,SETFD	;TERMINATE I/O PACKET
	MOVL	BUFHDR,SETFD+4	;SAVE TRANSFER DIRECTION
	MOVL	BUFHDR+4,SETFD+8	; BLOCK #
	MOVL	BUFHDR+8,SETFD+12	; NO. BYTES IN BUFFER
	MOVZWL	#SS$_NOWRT,SETFD+16	; IOSB 1
	CLRL	SETFD+20	; IOSB 2	; ALWAYS fail
	movl	#setfdl,r4
	$qiow_s efn=#1,chan=vdchn, -
	iosb=#iosb,func=#<io$_format+128>,p1=setfd,p2=R4
	ON_ERR	FDHostD_EXIT	; SKIP OUT IF ERROR
; NOW DONE TRANSFER
	CLRL	IOPROG	; SAY NO I/O IN PROCESS IF WE ARE FORCED TO EXIT
	JMP	EVTLOOP
; reading the virtual disk
READOP:
; READING DATA TO CLIENT. MUST GET DATA, THEN SEND TO DRIVER.
	MOVL	BUFHDR+4,R0	;GET BLOCK NUMBER
;	INCL	R0		;MAP TO VBN
	MOVL	R0,DRAB_BLK+RAB$L_BKT	;SET IT UP
	movw	#512.,drab_blk+rab$w_rsz ;512 byte blks
; LOOP OVER BLKS IN REQUEST
	movl	bufhdr+8,r6	;get bytecount to move
	addl2	#511,r6		;round up
	ashl	#-9,r6,r6		;convert to blks
; r6 is not messed up by movc3...
	movab	buf,r7		;scratch buffer address
				;(8K + header)
	movl	#1,setfd+12	;initial success return
16$:
	movl	drab_blk+rab$l_bkt,r5	;r5 gets block number
					;desired
	jsb	mov2rec		;move tape to desired record
; r0 returns i/o status
; r9 returns address of cache containing data image
; r5 remains block no.
	movl	setfd+12,r1	;see if errors recorded
	blbc	r1,176$		;if so, leave first one
	movl	r0,setfd+12	;return i/o code
176$:
	jsb	getdat
	tstl	r10		;if lo blk# negative, serious error
	bgeq	1176$
	brw	fdhostd_exit	;lose
1176$:
;r9 returns with start byte of this block
;	$read	rab=drab_blk

;	ON_ERR	FDHostD_EXIT	; SKIP OUT IF ERROR
;;	pushl	r6
;;	movl	drab_blk+rab$l_bkt,r6	;pass block number to crypt
;;	jsb	decrypt		; decrypt recbuf
;;	popl	r6
;	movab	recbuf,r9	;data from here
	movl	r7,r8		;data to here
	MOVC3	#512,(r9),(R8)	; STORE THE DATA IN OUR SPACE
	addl2	#512,r7		;pass this blk's data
	incl	drab_blk+rab$l_bkt ;pass this blk in file too
	decl	r6		;count down blks to do
	bgtr	16$		;copy all blks
	movab	buf,r2
	ADDL3	#20,BUFHDR+8,SETFD+8	; GET LENGTH TO XFER
	MOVAB	BUFHDR,SETFD+4	;BUFFER HDR ADDRESS
	MOVL	#2,SETFD	;HOST TO DRIVER COPY
	movl	#setfdl,r4
;	movl	#1,setfd+12	;success...
	movl	bufhdr+8,setfd+16	;/length sent
	$qiow_s efn=#1,chan=vdchn, -
	iosb=#iosb,func=#<io$_format+128>,p1=setfd,p2=R4
	ON_ERR	FDHostD_EXIT	; SKIP OUT IF ERROR
; NOW DATA IS IN DRIVER SPACE AS REQUIRED
COMMON:
; NOW TERMINATE THE I/O AND AWAIT MORE WORK.
	MOVL	#1,SETFD	;TERMINATE I/O PACKET
	MOVL	BUFHDR,SETFD+4	;SAVE TRANSFER DIRECTION
	MOVL	BUFHDR+4,SETFD+8	; BLOCK #
	MOVL	BUFHDR+8,SETFD+12	; NO. BYTES IN BUFFER
	MOVZWL	#SS$_NORMAL,SETFD+16	; IOSB 1
	CLRL	SETFD+20	; IOSB 2	; ALWAYS SUCCESS
	movl	#setfdl,r4
	$qiow_s efn=#1,chan=vdchn, -
	iosb=#iosb,func=#<io$_format+128>,p1=setfd,p2=R4
	CLRL	IOPROG	; SAY NO I/O IN PROCESS IF WE ARE FORCED TO EXIT
	ON_ERR	FDHostD_EXIT	; SKIP OUT IF ERROR
; NOW DONE TRANSFER
	JMP	EVTLOOP
; BE SURE WE DON'T LEAVE THE CHANNELS ASSIGNED TO THE DEVICES
; EITHER...
	$DASSGN_S CHAN=VDCHN
	RET
FDHostd_exit:
	tstl	ioprog	;i/o going?
	beql	1$	;if no, branch
	brw	ioxit	;else cleaN UP
1$:
	RET
;
; KERNEL ARG LIST
K_ARG:
	.LONG	2	;2 ARGS: fd device name, mb device name
	.ADDRESS	VDV_BUF_DESC
	.address	mbx_buf_desc

; BASHUCB - AREA TO MESS UP UCB WITH OUR FILE DATA
; BEWARE BEWARE BEWARE
;  runs in KERNEL mode ... HAS to be right.

	.ENTRY	BASHUCB,^M<R2,R3,R4,R5,R6,R7,R8>
; TAKEN LOOSELY FROM ZERO.MAR
; Obtains host's PID, and also sets up correct size in driver UCB
; both by cylinder and by block.
	.if	df,$$xdt
	jsb	g^ini$brk	;call xdt
	.endc
	.if	ndf,vms$v5
	MOVL	G^SCH$GL_CURPCB,R4	;;; NEED OUR PCB
	.iff
	MOVL	G^CTL$GL_PCB,R4		;;; NEED OUR PCB (VMS V5)
;;; (gets it in internal form, just as needed)
	.endc
;;; NEED IPID FOR DRIVER'S CALL TO SCH$POSTEF TO THIS HOST!!
	MOVL	PCB$L_PID(R4),OURPID	;;;SAVE OUR PID IN INTERNAL FORM
	JSB	G^SCH$IOLOCKW		;;; LOCK I/O DATABASE
	CLRL	HSTUCB			;;; ZERO "HOST" UCB
	tstl	clrcnt		;;;just zeroing count?
	bneq	126$
	movl	8(ap),r1		;;;get mailbox info first
	jsb	g^ioc$searchdev
	blbc	r0,59$			;;;on failure, give up
	movl	r1,mbucb		;;;store away mailbox UCB
126$:	MOVL	4(AP),R1		;;; ADDRESS DVC NAME DESCRIPTORS
	JSB	G^IOC$SEARCHDEV		;;; GET UCB ADDRESS INTO R1
	BLBS	R0,60$
59$:	BRW	BSH_XIT
60$:
; BUGGER THE UCB
; ASSUMES FILE LBN AND SIZE ALREADY RECORDED
; ALSO ASSUMES THAT ZERO LBN OR SIZE MEANS THIS ENTRY NEVER CALLED.
; (REALLY ONLY WORRY ABOUT ZERO SIZE; IF WE OVERMAP A REAL DEVICE
; THEN ZERO INITIAL LBN COULD BE OK.)
;
; Set device size. Since this is true of any disk, just use the offsets.
; No need for duplicating the UCB defs here.
	tstl	clrcnt		;;;just zeroing use count
	beql	127$		;;;if eql, no, normal ops
	movw	#1,ucb$w_refc(r1)	;;;zero ref count (in case it got set -1)
;;; (note we set it to 1 so it decrements to 0 on our exit.)
	BICW	#UCB$M_ONLINE,UCB$W_STS(R1) ;;; FLAG OFFLINE
	BICW	#UCB$M_VALID,UCB$W_STS(R1) ;;; AND VOL INVALID
	brb	128$		;;;exit, success
127$:
;
	tstw	ucb$w_refc(r1)	;;;fix up stray ref counts
	bneq	140$		;;;
142$:	movw	#1,ucb$w_refc(r1)	;;;if it was 0, keep from getting 65535
	brb	141$
140$:
	cmpw	ucb$w_refc(r1),#65533	;;;small neg numbers also look bugus
	bgtru	142$			;;;so fix these up also
141$:
	MOVL	HSTFSZ,UCB$L_MAXBLOCK(R1) ;;; (SAVE SIZE TWICE, FOR RMS
	MOVL	HSTFSZ,R0		;;; GET HOST SIZE IN CYLINDERS
	ASHL	#-6,R0,R0		;;; GET # CYLINDERS IN SIZE NOW
	MOVW	R0,UCB$W_CYLINDERS(R1)	;;; SAVE IN UCB FOR REST OF VMS
; This computation is redone in fddrv itself, but do it here also.
; It assumes in fddrv that there are 64 sectors/cylinder.
	BISW	#UCB$M_ONLINE,UCB$W_STS(R1) ;;; FLAG ONLINE NOW
	BISW	#UCB$M_VALID,UCB$W_STS(R1) ;;; AND VOL VALID
;;; THAT'S IT... SHOULD BE OK NOW.
128$:	MOVL	#SS$_NORMAL,R0
BSH_XIT:
	PUSHL	R0
	JSB	G^SCH$IOUNLOCK		;;; UNLOCK I/O DATABASE (DROP IPL)
	POPL	R0			;;; REMEMBER R0
	RET	;;; BACK TO USER MODE NOW
ourpid:	.long	0	;;;store this locally
CLRCNT:	.long	0	;1 if clearing ref cnt ucb$w_refc
;;;(avoid paging problems in kernel)
; EXIT HANDLER
; CLEARS I/O ASSIGNMENT TO FD: UNIT
;
	.ENTRY	XITHDL,^M<R2,R3,R4,R5,R6>
ioxit:	TSTL	IOPROG
	BEQL	1$
	MOVL	#1,SETFD	;TERMINATE I/O PACKET
	MOVL	BUFHDR,SETFD+4	;SAVE TRANSFER DIRECTION
	MOVL	BUFHDR+4,SETFD+8	; BLOCK #
	MOVL	BUFHDR+8,SETFD+12	; NO. BYTES IN BUFFER
	MOVZWL	#SS$_ACCVIO,SETFD+16	; IOSB 1
	CLRL	SETFD+20	; IOSB 2	; FAILURE
	movl	#setfdl,r4
	$qiow_s efn=#1,chan=vdchn, -
	iosb=#iosb,func=#<io$_format+128>,p1=setfd,p2=R4
1$:
	CLRL	SETFD	;DECLARE/UNDECLARE
	PUSHAB	DESBLK		; ADDRESS OF DESBLK
	CALLS	#1,G^SYS$CANEXH	; CANCEL EXIT HANDLER
	clrl	setfd+4	;FLAG NOBODY HOME NOW
	clrl	setfd+8
	movl	#setfdl,r4
	$qiow_s efn=#1,chan=vdchn, -
	iosb=#iosb,func=#<io$_format+128>,p1=setfd,p2=R4
; declare host no longer is home.
	RET			; FINISH EXIT
;
; MOV2REC - move to a record
;	movl	drab_blk+rab$l_bkt,r5	;r5 gets block number
					;desired
;	jsb	mov2rec		;move tape to desired record
; r0 returns i/o status
; r9 returns address of cache containing data image
; r5 remains block no.
;	movl	setfd+12,r1	;see if errors recorded
;	blbc	r1,176$		;if so, leave first one
;	movl	r0,setfd+12	;return i/o code
;176$:
;	jsb	getdat
;r9 returns with start byte of this block
;cacheidx has index to cache from vmloadr to vmhiadr in blocks size fd_siz
;backfg says if backup
;fd_tbf = approx blk factor (exact if not backup)
;curlblk = lo blk of currec position
;currec=current record on tape
;opcnt=operation counter
fdxj:
	popl	r7
	popl	r6
	popl	r5
	popl	r4
	tstl	(sp)+	;junk jsb call
	brw	fdhostd_exit
	.globl	mov2rec
mov2rec:
	pushl	r4
	pushl	r5
	pushl	r6
	pushl	r7
	movl	#3,xrg11	;count max times into getgrp
	movl	#1,r0	;success return initially
;first seek data in cache
777$:	clrl	r9
	jsb	cachluk	;return r9=cache blk if we find blk
	tstl	r9	;got data?
	beql	1101$
	brw	1$
1101$:
;	bneq	1$
;get approx. idea how far to move to get to data.
	subl3	curlblk,r5,r4	;r4 = blks to move
	clrl	r11		;adjust flag setup
14$:	divl2	fd_tbf,r4	;divide by blk factor
	tstl	backfg
	bneq	114$
;in image mode too we have to back up an extra record to get
; to before the record that curlblk points at (as reset after
; getdat call)
	tstl	r4
	bgeq	114$		;if r4 is non negative skip
	decl	r4		;else skip back one more
114$:
; this should give desired skip count
; adjust since we need to read forward, so decrement one
	incl	joggle
	decl	r4
;normally, save at start, cachluk would find blks in current buffer.
	beql	2$	;if skip count=0, no qio
	movl	r4,wrk+4
	addl3	r4,currec,r1	;be sure we don't skip back to before file mark
	bgeq	17$		;if >= 0 all's ok
;foo...too far back. clamp.
	mnegl	currec,r4	;go back only to after filemark
	movl	r4,wrk+4
	beql	2$		;if zero skip the qio
17$:
;	$qiow_s	#2,ddchn,#io$_skipfile,iosb,,,r6,,,,,
;	$qiow_s chan=ddchn,func=#io$_skiprecord,iosb=iosb,p1=wrk+4
;	$qiow_s #2,ddchn,#io$_skiprecord,iosb,wrk+4,,,,,
	clrq	-(sp)
	clrq	-(sp)
	pushl	#0
	pushl	wrk+4
	clrq	-(sp)
	pushab	iosb
	movzwl	#io$_skiprecord,-(sp)
	movzwl	ddchn,-(sp)
	pushl	#2
	calls	#12,g^sys$qiow
	on_err fdxj	;failure to skip is a BIG problem
;note this checks that the qio gets issued only
	addl2	r4,currec	;maintain current position
	movl	iosb,r0		;result code of I/O
;if we hit EOF, something went wrong really grossly. 
;	cmpw	r0,#ss$_endfile	;so check eof
;	bneq	2$		;if not branch
;foo...saw eof...
;if backing up go fwd 1
;	tstl	r4
;	bgtr	102$		;if going fwd skip
;	jsb	resetrec1	;reposition to start of file
;	brb	2$
;102$:
; if going forward, back up a couple records. By ignoring xor blks
; we normally should never overshoot but it is possible to get a
; multivolume saveset. In that case these two routines will need
; to be aware of changing volumes on the tapes too. Because this
; is awkward as heck, it is STRONGLY discouraged and not supported
; initially at least. (Bad enough to thrash (potentially) between
; long separated areas of A tape without having to have a human
; swapping tapes heavily into the bargain.)
;	jsb	resetend	;position at end, or on next volume...
;
2$:
; find a slot in cache we can use
	jsb	cachget	;r9 returns data addr
			;r8 returns index location
	movl	#10,rg11
6$:	movl	r9,wrk+4
;	$qiow_s	chan=ddchn,func=#io$_readlblk,iosb=iosb,p1=wrk+4,p2=fd_siz
	clrq	-(sp)
	clrq	-(sp)
	pushl	fd_siz
	pushl	r9		;address
	clrq	-(sp)	;no asts
	pushab	iosb
	movzwl	#io$_readlblk,-(sp)
	movzwl	ddchn,-(sp)
	pushl	#2
	calls	#12,g^sys$qiow
	on_err fdxj	;can't do i/o => fatal
; iosb errs need more tolerance
	incl	currec		;should be past 1 more rec.
	movl	iosb,r0		;get i/o result
;	cmpw	r0,#ss$_endfile	;so check eof
;	bneq	106$		;if not branch
;foo...saw eof...
;if backing up go fwd 1
;	tstl	r4
;	bgtr	102$		;if going fwd skip
;	jsb	resetrec1	;reposition to start of file
;	brb	106$
;105$:
; if going forward, back up a couple records. By ignoring xor blks
; we normally should never overshoot but it is possible to get a
; multivolume saveset. In that case these two routines will need
; to be aware of changing volumes on the tapes too. Because this
; is awkward as heck, it is STRONGLY discouraged and not supported
; initially at least. (Bad enough to thrash (potentially) between
; long separated areas of A tape without having to have a human
; swapping tapes heavily into the bargain.)
;	jsb	resetend	;position at end, or on next volume...
;
;;;;;
106$:
	incl	r4		;account for read now
	mull2	fd_tbf,r4	;mult by blk factor
	addl2	r4,curlblk	;maintain blk position if not backup
				;(handle backup in getdat if needed)
	tstl	backfg		;skip xors fast here
	beql	5$
; see if xor block (if xor, applic field=2, else 1)
	cmpw	#1,bbh$w_applic(r9)	;if attr ne 1 then it's either xor or gross error
	bneq	8$		;so go ahead only if not xor
; Check crc before seeing if local I/O was good. Good CRC should mean data ok
	tstl	crcfg
	bneq	208$		;if no crcs here, skip check
	jsb	crcck		;crc ok?
	blbc	r0,8$		;if not try reading more
208$:
; if we get error on the I/O, also retry
; (might be OK to rely only on CRC; if doing so comment next inst.)
	movl	iosb,r0
	blbs	r0,5$		;if i/o was ok, branch
;skip up to 10 losing records
;note fine-tuning below may attempt reposition also
8$:	decl	rg11		;count down
	bleq	206$
	brw	6$		;and read next
206$:
;	bgtr	6$		;and read next
; if we can't find the data, try xor group
	decl	xrg11		;only do this at most 3 times per blk looked
	bleq	205$		;for...otherwise just give it up
; (xrg11 prevents long infinite loops via positioning screwups and
;  xor block failures due to getting wrong group. These should never
;  occur, but tape hardware is NOT always error free and this kind
;  of thing must be guarded against.)
	tstl	ixorfg		;if ignore xor forced skip also
	bneq	205$		;even if it otherwise would be OK
	jsb	grpget		;total failure...try using xor group
	blbc	r0,205$
;seems we got it ok. Look in cache for data
	brw	777$
205$:
; return an erroneous record since we can't do any better
	brw	1$
;	brw	fdxj	;fatal error...can't get good record
5$:
; lo blk this record should be old lo blk + r4*fd_tbf
	tstl	backfg
	bneq	1111$
	movl	currec,curlblk
	mull2	fd_tbf,curlblk	;tightly couple currec & curlblk in image mode
; (curlblk gets reset to fd_tbf later as result of getrec.)
1111$:
;maintain cache index
; this has to reflect what we just read, not where we are now
; so subtract off a block's worth
	movl	currec,(r8)
	movl	curlblk,4(r8)
	subl2	fd_tbf,4(r8)
	movl	curlblk,8(r8)	;end lbn if image
	decl	8(r8)		;account for origin no.
	movl	opcnt,12(r8)
	blbs	r0,3$		;if i/o worked ok, all well
;failure on i/o
;no help for it if image, but can try more if backup
	tstl	backfg
	bneq	3$
	brw	1$
;	beql	1$		;just exit if image tape
;had error and it's vms backup
3$:
;ok i/o but test for xor blk or wrong numbewr and finetune position
;then fix curlblk and rest of cache index.
;get limits of this blk
	jsb	getlims		;r10 returns as lbn, r11 as high lbn
	tstl	r10		;r10 must be >0
	bgeq	1110$
; neg r10 on return means data looked wrong...maybe an xor or such...
;note this can ONLY happen in backup mode
	clrl	(r8)
	clrl	4(r8)
	clrl	8(r8)
	clrl	12(r8)		;remove the index entry so we don't reuse junk
	movl	r5,r10		;best guess is read next record
	subl2	fd_tbf,r10	;so arrange to just do so
	movl	joggle,r11
	pushl	r1
	pushl	r2
	ediv	#3,r11,r1,r2
	tstl	r2		;remainder 0?
	bneq	1103$		;if not branch
	subl2	fd_tbf,r10	;so arrange to just do so
;however jog it off a possible loop if we can
1103$:	popl	r2
	popl	r1
	movl	r10,r11
	brb	110$		;also don't update index
1110$:
	movl	r10,curlblk	;keep the info around
	tstl	backfg		;backup mode?
	beql	110$		;if not branch
	movl	r11,8(r8)	;set correct end LBN
	movl	r10,4(r8)	;and start LBN
110$:
;check our blk is found. Do repositioning separately here since we
;must avoid an infinite loop.
	cmpl	r5,r10		;block in range?
	blssu	10$		;branch if not
	cmpl	r5,r11		;test high range
	blequ	1$		;if too high, fall through
				;(equal means ok)
10$:
; the desired block is not the one we read in.
; if we have had an error reading, do not mess around, just return an
; error; this is flagged by r0 containing an error code and is done
; to prevent infinite loops.
	blbs	r0,11$
	movl	#ss$_fcpreaderr,r0	;flag things are really messed up
	brw	1$			;and leave
11$:	subl3	r10,r5,r4		;how far are we from the block we want?
; desired blk - lo blk this buffer -> r4
;round up to next record multiple on tape
	subl3	rg11,#10,r10		;get number of retries that may have been tried
	tstl	r4
	bgtr	111$
	subl2	fd_tbf,r4		;back up 1 more
					;to get back
	bitl	#3,joggle		;sometimes...
	beql	111$
	subl2	fd_tbf,r4		;back up 1 more
					;to get back
; back up two where we had troubles finding things
111$:	brw	14$			;reuse code for actual I/O
;block is in memory now.
;r0 should reflect status
1$:
	popl	r7
	popl	r6
	popl	r5
	popl	r4
;
	rsb
; getdat - At entry, r9 points to the data block and r5 has the
; desired block number.
; on exit r9 should point to data area we want
getdat:
	pushr #^m<r0,r1,r2,r3,r4,r5,r6,r7>
	tstl	backfg		;backup mode?
	beql	10$		;if not branch
	movl	#-1,r10		;flag if we find nothing sensible
	movzwl	(r9),r0		;count of bytes in block hdr
	movl	r9,r1		;use r1 as work area
;pass block hdr
	addl2	r0,r1
;following records are preceded by 16 byte headers
3$:	movzwl	(r1),r2		;get record size
	bleq	2$		;if invalid, skip out
	cmpw	#6,2(r1)	;see if this is an LBN record
	beql	1$		;if yes branch
;wrong record type; pass it.
	addl2	r2,r1		;get..
	addl2	#16,r1		;to next record start
;sanity test next
	subl3	r9,r1,r3	;check if we've gotta be past record
	cmpl	r3,fd_siz	;see if bigger than our blocks
	bgtru	2$		;if so branch
	brb	3$
1$:	movl	brh$l_address(r1),r10	;low blk
	ashl	#-9,r2,r11	;get number blks in this record
	decl	r11		;since we're getting rec. nos, must
				;allow for offset of 1
;(start rec=5, nrecs=4 means top record=8, not 9)
	addl2	r10,r11		;r11 is now high block
	subl3	r10,r5,r3	;r3 now is offset into block
	blss	2$		;skip if error
	ashl	#9,r3,r3	;make a byte offset
	addl2	#16,r3		;pass header to data
	addl2	r1,r3		;now r3 is data
	movl	r3,r9
2$:
	popr #^m<r0,r1,r2,r3,r4,r5,r6,r7>
	rsb
10$:
;assume r8 points at cache index area for this data
	movl	4(r8),r10	;lo lbn
	movl	8(r8),r11	;hi lbn
	subl3	r10,r5,r0	;r0 = blk offset (desired - min this cache blk)
	ashl	#9,r0,r0	;make a byte offset
	addl2	r0,r9		;point r9 at our blk
	popr #^m<r0,r1,r2,r3,r4,r5,r6,r7>
	rsb
;find block containing block # in r5 in cache if it is there
;r9 returns address if found, else remains zero
cachluk:
	pushl	r0
	pushl	r1
	pushl	r2
	pushl	r3
	clrl	r9
	movab	cacheidx,r0	;start of cache
	movl	r0,r2		;need this later
	movl	cachecnt,r1	;number cache items
1$:	cmpl	r5,4(r0)	;blk number less than cache min?
	blssu	2$		;if so branch to next entry
	cmpl	r5,8(r0)	;r5 higher than end lbn of cached entry?
	bgtru	2$		;if so update and keep looking
; found the block
	movl	opcnt,12(r0)	;update cache's used time
	subl3	r2,r0,r3	;r3 gets offset to cache entry
	ashl	#-4,r3,r3	;shift off low 4 bits (4 longs=16 bytes)
				;to get offset in entries
	mull2	fd_siz,r3	;mult by blocksize  to get addr offset
	addl3	vmloadr,r3,r9	;return start addr of block in r9
	brb	3$
2$:	addl2	#16,r0	;pass to next cache index item
	sobgtr	r1,1$		;keep looping if no find yet
; if we fall thru it isn't there...
3$:
	movl	r0,r8		;return cache index in r8
	popl	r3
	popl	r2
	popl	r1
	popl	r0
	rsb
cachget:
; r9=data addr, r8=index addr on return
	pushr #^m<r0,r1,r2,r3,r4,r5,r6,r7,r10,r11>
	movab	cacheidx,r0	;start of cache
	movl	r0,r2		;need this later
	movl	r0,r4
	movl	cachecnt,r1	;number cache items
	movl	#^xffffffff,r3	;"min" offset
1$:	tstl	12(r0)		;empty entry?
	beql	2$		;if so grab it
	cmpl	r3,12(r0)	;see if use cnt < curr min
	blequ	4$		;if r3 (min) lt this, this more recent
	movl	r0,r4		;r4=min candidate
	movl	12(r0),r3	;new min
4$:
	addl2	#16,r0		;next index
	sobgtr	r1,1$		;seek
; no unused entries found...look for min
	movl	r4,r0		;use min. used (LRU) entry
2$:	subl3	r2,r0,r3	;offset to cache entry
	clrl	(r0)		;clear out all of cache index
	movl	#-1,4(r0)		;except LRU "time"
	movl	#-1,8(r0)		;so we don't mistake identity anywhere
; assume -1 is not a valid block number.
	ashl	#-4,r3,r3	;shift off low 4 bits (4 longs=16 bytes)
				;to get offset in entries
	mull2	fd_siz,r3	;mult by blocksize  to get addr offset
	addl3	vmloadr,r3,r9	;return start addr of block in r9
	movl	opcnt,12(r0)	;store current op into cache index
	movl	r0,r8		;return index loc
	popr #^m<r0,r1,r2,r3,r4,r5,r6,r7,r10,r11>
	rsb
getlims:
;r10=lo lbn,r11=hi lbn on return
; trivial implementation..use getdat but preserve r9 across the call
	pushl	r9
	jsb	getdat
	popl	r9
	rsb
; crc check
; entry: r9 points to data block
; exit: r9 and data blk unaltered, r0=1 if ok, else 2
crcini:	.long	0

; The data block is CRC checked using the autodin II polynomial
; as below, with the CRC field zero. The header itself is CRCd with
; the CRC16 polynomial also. XOR blocks xor everything after the
; block label record.
pn:	.long	^XEDB88320	;autodin polynomial
tbl:	.blkl	16
pg:	.long	2
	.address	pn
wta:	.address	tbl
ini:	.long	-1
;data descriptor
dtnm:	.word	65535	;fill in real length
	.byte	dsc$k_dtype_t	;text string
	.byte	1	;fixed
dtad:	.address	dtad	;address of data, really...fill in
; fill in address of real data
crcset:	pushr	#^M<r0,r1,r2,r3,r4,r5,r6,r7,r8,r9,r10,r11>
	movw	fd_siz,dtnm	;fill in data size
	movl	r9,dtad
	callg g^pg,g^lib$crc_table	;generate crc table
	movl	#1,crcini	;do tbl once only
	popr	#^M<r0,r1,r2,r3,r4,r5,r6,r7,r8,r9,r10,r11>
	rsb
; the crc routine's tests are commented presently.
crcck:
	tstl	crcini
	bneq	1$
	jsb	crcset	;set up our CRC block so the CRC instruction will work right
1$:	pushl	r3
	pushl	r4	;ned some regs
	pushl	r5
	pushl	r6
	movl	#1,r0	;assume ok
	movl	r9,dtad	;point at real data
	movl	bbh$l_crc(r9),r3	;save crc
	clrl	bbh$l_crc(r9)		;clear for comparison
;chksum of hdr at 254-255 = crc16 of hdr
	movw	254(r9),r4
; let this crc be 0 at start also.
	clrw	254(r9)
; assume that for block crc calc, header crc was in place
; already.
	movzwl	dtnm,r5		;length
	movl	dtad,r6		;data addr
	pushl	r3	;crc inst trashes
; put in other possibilities to allow me to see which works
	pushl	r11
	movab	tbl,r11
	crc	(r11),ini,r5,(r6)
	popl	r11
	popl	r3
	mcoml	r0,r0		;complement r0 for crc
	cmpl	r0,r3		;crc match?
	beql	2$		;yes, ok
	movl	#2,r0		;else flag err
	brb	3$
2$:	movl	#1,r0
3$:	movw	r4,254(r9)	;restore hdr chksum
	movl	r3,bbh$l_crc(r9)
	popl	r6
	popl	r5
	popl	r4
	popl	r3
	rsb
;
; GETGEOM  -  get geometry out of physical disk
; data record (vms backup only)
; entry: r3 points at record
; exit: secs, trks, cyls, hstfz have device size
getgeom:
	pushr #^m<r0,r1,r2,r3,r4,r5,r6,r7>
	movzwl	-16(r3),r7	;size of record
	addl2	r3,r7		;highest address (for end check)
	addl3	#2,r3,r0	;point at data types with r0
; 58 = sectors
; 59 = trks
; 60 = cylinders
; 61 = device size types
100$:
	movzwl	(r0)+,r1	;size of data
	beql	200$		;zero size means should be the end
	movzwl	(r0)+,r2	;type flag
	movl	(r0),r4		;get data (maybe with up to 3 bytes junk)
	addl2	r1,r0		;pass data
; now if this data is interesting pick it out
	cmpw	#58,r2		;sectors?
	bneq	1$		;if not skip
	movzbl	r4,secs		;else save data
1$:	cmpw	#59,r2		;tracks?
	bneq	2$
	movzbl	r4,trks		;save tracks if so
2$:	cmpw	#60,r2		;cylinders?
	bneq	3$
	movzwl	r4,cyls		;save cylinders if so
3$:	cmpw	#61,r2		;overall size?
	bneq	4$
	movl	r4,hstfz	;save size if so
4$:
	cmpl	r0,r7
	blssu	100$		;if not at end keep looking
200$:
	popr #^m<r0,r1,r2,r3,r4,r5,r6,r7>
	rsb
getxor:
	pushr #^m<r0,r1,r2,r3,r4,r5,r6,r7>
	movzwl	-16(r3),r7	;size of record
	addl2	r3,r7		;highest address (for end check)
	addl3	#2,r3,r0	;point at data types with r0
; 58 = sectors
; 59 = trks
; 60 = cylinders
; 61 = device size types
100$:
	movzwl	(r0)+,r1	;size of data
	beql	200$		;zero size means should be the end
	movzwl	(r0)+,r2	;type flag
	movl	(r0),r4		;get data (maybe with up to 3 bytes junk)
	addl2	r1,r0		;pass data
; now if this data is interesting pick it out
	cmpw	#14,r2		;xor factor?
	bneq	1$		;if not skip
	movzwl	r4,xorsiz	;else save data
	incl	xorsiz		;bump xorsize to include xor block
	cmpl	xorsiz,#xormx	;too big to use?
	bleq	200$		;if leq no, looks ok
	incl	ixorfg		;else flag no xor action
1$:
	cmpl	r0,r7
	blssu	100$		;if not at end keep looking
200$:
	popr #^m<r0,r1,r2,r3,r4,r5,r6,r7>
	rsb
;
; GRPGET - get a complete XOR group
; Assumes we are positioned approximately at the correct record but
; that it gives invalid CRC and that we have to drop back to use the
; XOR groups. Action is as follows:
; 1. Backspace 1.5 xor groups back to ensure we pass an xor record
;    and can find one reading forward
; 2. Read data until we get an xor record (for the preceding group)
; 3. Read data into fd_buf fixed area and check CRC
; 4. Use sequence number to place data of good CRC records into xor
;    area at xoradr and up. Invalid CRC data does not get copied
;    there. (Trust the CRC even if hardware error is signalled.)
; 5. If a bad CRC is encountered, flag it
; 6. Read next record. If same sequence number as last and last was
;    bad CRC, and this CRC is good, erase bad CRC flag and copy
;    data.
; 7. Continue until we get an XOR block (or have read xorsiz sequence
;    numbers)
; 8. If a second bad crc block is found (noting that it might disappear by
;    having the seq # rerecorded) we fail and just return an error
; 9. If only one bad CRC is found, zero that block and regenerate it
;    from the XOR of the other XORSIZ-1 blocks in the group
;10. Get a cache area in the normal region and copy all the blocks in
;    the xor group into the normal cache (one at a time), filling in the
;    header appropriately. Return success,
; entry: r5 is block number desired, opcnt, currec, and curlblk
;  are set up. rg11 has counted down from 10 retries, so initially one
;  needs to back up by 10 records plus the xorsiz*1.5 count.
grpget:
	pushr	#^m<r1,r2,r3,r4,r5,r6,r7,r8,r9,r10,r11>
	tstl	crcfg		;can't do this unless we have crc
	beql	2$
1$:	brw	9999$
2$:	tstl	xorsiz		;enough space for xors?
	beql	1$		;if not exit fast
	movl	#2,r0		;assume we can't get data this way either
	clrq	xseq1
	clrq	xbadcrc		;initialize locally used data
	clrl	xcnt
;first back up appropriate no. records
	movl	xorsiz,wrk
	ashl	#-1,wrk,wrk	;xorsiz/2
	addl2	xorsiz,wrk	;+xorsiz
; since we will sometimes bounce around to get here, try and see if
;we should back up another 10 records. If we seem to be in the right xor group, 
;don't move too far off.
;this will probably be the usual path.
	subl3	curlblk,r5,r11	;see if we are near desired blk
	bgtr	5$
	mnegl	r11,r11		;r11 is "distance" to desired lbn
5$:	cmpl	r11,xorsiz	;see if over xorsiz
	bleq	6$		;if closer than xorsiz do NOT skip back too far
	addl2	#10,wrk		;+10
	subl2	rg11,wrk	;-rg11 (if didn't do all retries)
6$:
	cmpl	wrk,currec	;don't back up past start of file
	bleq	7$		;if leq all well
	movl	currec,wrk	;else just go back to start
7$:
	mnegl	wrk,wrk		;negate since we skip back
;	$qiow_s	#2,ddchn,#io$_skiprecord,#iosb,#-1,,,,,
	clrq	-(sp)
	clrq	-(sp)
	pushl	#0
	pushl	wrk	;pass rec cnt by ref
	clrq	-(sp)
	pushab	iosb
	movzwl	#io$_skiprecord,-(sp)
	movzwl	ddchn,-(sp)
	pushl	#2
	calls	#12,g^sys$qiow
	addl2	wrk,currec	;set current record as it should be
	mull2	fd_tbf,wrk	;get approx new lblk
	addl2	wrk,curlblk	;and update that
	On_ERR	9999$
	movl	iosb,r0
	On_ERR	9999$
; now search for an xor record so we can start at "current" xor group
; (as of the call here, that is.)
	movl	#35,r2	;safety count
10$:	$qiow_s	chan=ddchn,func=#io$_readlblk,iosb=iosb,p1=fd_data,p2=fd_siz
	incl	currec
	addl2	fd_tbf,curlblk
	On_ERR	9999$
	movl	iosb,r0
	On_ERR	9999$
	decl	r2
	bgtr	19$
	brw	9999$		;lose on countdown
19$:	cmpw	#2,bbh$w_applic+fd_data
	bneq	10$
; here should be positioned at first real record of this xor group
; zero out data area first
	movl	xorsiz,r7
	movl	xoradr,r8	;data area
16$:
	pushl	r5
	pushl	r0
	movc5	#0,(r8),#0,fd_siz,(r8)	;;;!!! check format...zero a blk
	popl	r0
	popl	r5
	addl2	fd_siz,r8
	sobgtr	r7,16$				;do all buffers
;read it and get low seq number etc.
	movl	xorsiz,r6	;number seq #s to do
	$qiow_s	chan=ddchn,func=#io$_readlblk,iosb=iosb,p1=fd_data,p2=fd_siz
	incl	currec
	addl2	fd_tbf,curlblk
	On_ERR	9999$
	movab	fd_data,r9
	movl	bbh$l_number(r9),xseq1	;low seq number
	movl	xseq1,r11		;store for later comparison in loop too
	movl	xoradr,xcnt		;store addr of data area
	jsb	crcck			;see if data crc is ok
	blbs	r0,11$			;if crc is ok branch
;bad crc...
	tstl	xbadcrc		;bad crc seen already?
	beql	12$
	tstl	xbadcrc+4
	beql	13$
113$:	brw	9999$		;fail if see 3rd bad crc
13$:
	movl	xbadcrc,xbadcrc+4	;push down bad crc
12$:
	movl	bbh$l_number(r9),xbadcrc	;store seq # with bad crc
;go retry now
	brb	20$
11$:
;see if we can pop up bad crc # from earlier seq #
;noop for first go...
	movl	xcnt,r8
	pushl	r5
	pushl	r0
	movc3	fd_siz,(r9),(r8)	;copy the data
	popl	r0
	popl	r5
20$:
; here loop to get next record(s)
	$qiow_s	chan=ddchn,func=#io$_readlblk,iosb=iosb,p1=fd_data,p2=fd_siz
	incl	currec
	addl2	fd_tbf,curlblk
	On_ERR	9999$
	movl	bbh$l_number(r9),r11	;sequence number this record
	jsb	crcck			;see if data crc is ok
	blbs	r0,21$			;if crc is ok branch
;bad crc...
	tstl	xbadcrc		;bad crc seen already?
	beql	22$
	tstl	xbadcrc+4
	beql	23$
	brw	9999$		;fail if see 3rd bad crc
23$:
	movl	xbadcrc,xbadcrc+4	;push down bad crc
22$:
	movl	bbh$l_number(r9),xbadcrc	;store seq # with bad crc
;go retry now
	cmpw	#1,bbh$w_applic(r9)	;another xor blk seen here?
	bneq	100$			;if so branch and see about xor fixup
	brb	20$
21$:
;crc good.
;see if we can pop up bad crc # from earlier seq #
;noop for first go...
	cmpl	r11,xbadcrc		;same seq # as late bad crc?
	bneq	25$			;if neq can't help it
	movl	xbadcrc+4,xbadcrc	;pop old bad crc
	clrl	xbadcrc+4		;and clean up evidence there had been another
25$:
;see if a repeat of prev rec so must back down xcnt
	subl	xseq1,r11		;offset in seq #s
; sanity check of seq #
;see we don't get too far
	movl	xorsiz,r10
	ashl	#1,r10,r10	;2*xorsiz
	cmpl	r11,r10		;seq # diff > 2*xorsiz?
	blss	26$		;if lss not too far out yet
28$:	brw	9999$		;else fail the operation
26$:
	mull2	fd_siz,r11		;turn into addr offset
	addl3	xcnt,r11,r8		;form data addr
	cmpl	r8,vmhiadr		;ensure not too high
	bgtru	28$			;if so fail
	pushl	r5
	pushl	r0
	movc3	fd_siz,(r9),(r8)	;copy the data
	popl	r0
	popl	r5
;this automatically overwrites data if it was multiply recorded
;we zeroed all first...
	cmpw	#1,bbh$w_applic(r9)	;another xor blk seen here?
	bneq	100$			;if so branch and see about xor fixup
;not an xor block and not end so get more
	brw	20$			;go grab next record folks
100$:
;now have all data
;must xor if it makes sense to do so
	tstl	xbadcrc+4		;got a 2nd bad crc?
	bneq	28$			;if nonzero we have...can't recover
;now we just do xors and put data into the cache
;assume success (unless we find illegal block format)
	movl	#1,r0
	movl	xbadcrc,r11		;bad-crc block seq
	beql	105$
	subl2	xseq1,r11		;get offset to data
	movl	r11,xcnt		;save base of our area
;loop over all blks forming xor, stashing in extra blk
	movl	xoradr,r7	;base addr
	movl	fd_siz,r4
	ashl	#-2,r4,r4		;form long count
103$:	movl	fd_siz,r8
	movl	xorsiz,r6	;# blks
	clrl	r10		;accum
102$:	xorl2	(r7),r10
	addl2	r8,r10		;next block offset
	sobgtr	r6,102$		;do all blks
	movl	r10,(r11)+	;store xor data
	tstl	(r7)+		;pass a word
	sobgtr	r4,103$		;do all longs of all buffers
;nbow xors are all computed; fill in 1st (xorsiz-1) blks into cache
105$:	movl	xorsiz,r6	;get # blks to do
	decl	r6		;(does not include xor blk)
	movl	xoradr,r7	;where data is
110$:	jsb	cachget		;find cache slot
	pushl	r5
	pushl	r0
	movc3	fd_siz,(r7),(r9)	;store data
	popl	r0
	popl	r5
	movw	#256,(r9)	;label size=256 always
;fill in directory
	movl	currec,(r8)	;curr. record approx
	movl	opcnt,12(r8)	;lru counter
	jsb	getlims		;get blk lims
	tstl	r10		;negative lo lbn?
	bgeq	120$
	clrl	12(r8)		;lose and declare failure
	clrl	(r8)
	movl	#4,r0		;losing return
	brb	9999$
120$:	movl	r10,4(r8)	;save lo lbn
	movl	r11,8(r8)	;and hi lbn
	addl2	fd_siz,r7	;to next address
	sobgtr	r6,110$		;do for all
	movl	#1,r0		;all's well if here
9999$:
	popr	#^m<r1,r2,r3,r4,r5,r6,r7,r8,r9,r10,r11>
	rsb
	.END FDHostD