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diff --git a/sys/mtio/mtopen.x b/sys/mtio/mtopen.x
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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<knet.h>
+include	<config.h>
+include	<syserr.h>
+include	<fset.h>
+include	<mach.h>
+include	"mtio.h"
+
+# MTOPEN -- Open a magtape file, or a regular binary file if the file name is
+# not "mt" prefixed.  Access modes are restricted to read_only, write_only,
+# append, and new_tape.  The buffer size argument specifies the size of the
+# FIO buffer used to access the tape; a system and device dependent default
+# is supplied if the buffer size is given as zero.  If the device is a fixed
+# block size device the buffer size will be adjusted to an integral multiple
+# of the device block size.  For variable size record devices, the buffer size
+# determines the size of the tape record on a write, or the maximum record
+# size on a read.
+# 
+# The device to be accessed is specified as follows:
+# 
+#	[node!] mtX [ '[' file[.record] [:attr-list] ']' ]
+# 
+# for example,
+# 
+#	mtexb1[4:nb:se@:ts=1200:so=/dev/ttya8]
+# 
+# The "mt" prefix is required for the object to be considered a magtape device
+# reference.  The device name returned is "mtX" as shown above; there must be
+# an entry for device mtX in the tapecap file in DEV.
+# 
+# The file and record numbers are optional.  Files and records are numbered
+# starting with 1.  A sequence such as "mtX[eot]" will cause the tape to be
+# positioned to end of tape.  "mtX[0]" causes the tape to be opened at the
+# current position, i.e., without being moved.
+# 
+# The optional attr-list field consists of a sequence of colon-delimited
+# tapecap fields.  These will override any values given in the tapecap entry
+# for the device.  The syntax for attr-list is the same as in tapecap.
+# 
+# If the filespec does not have the prefix "mt", we assume that the file is
+# a regular binary file and try to open that.  If a tape file is specified
+# then the drive must be allocated before we are called.  We allocate and
+# initialize an MTIO file descriptor and call FOPNBF to install the magtape
+# device in FIO and open the device/file.
+
+int procedure mtopen (mtname, acmode, bufsize)
+
+char	mtname[ARB]		#I device to be opened
+int	acmode			#I access mode
+int	bufsize			#I fio buffer size (record size) or 0
+
+bool	first_time
+pointer	sp, devcap, fname, gty
+int	mt, fd, nskip, new_file, new_record
+
+bool	streq()
+pointer	mt_gtyopen(), gtycaps()
+int	open(), fopnbf(), gtygets(), access()
+int	mt_skip_record(), mtfile(), mt_devallocated()
+extern	zopnmt(), zardmt(), zawrmt(), zawtmt(), zsttmt(), zclsmt()
+
+errchk	open, fopnbf, fseti, syserrs, mtparse
+errchk	mt_getpos, mt_skip_record, mt_gtyopen, gtygets, mt_glock, mtallocate
+data	first_time /true/
+include	"mtio.com"
+
+begin
+	call smark (sp)
+	call salloc (fname, SZ_PATHNAME, TY_CHAR)
+	call salloc (devcap, SZ_DEVCAP, TY_CHAR)
+
+	# Runtime initialization of the mtio file descriptor common.
+	# Make each file descriptor available for use.
+
+	if (first_time) {
+	    call mt_clrcache()
+	    do mt = 1, MT_MAXTAPES
+		MT_OSCHAN(mt) = NULL
+	    first_time = false
+	}
+
+	# If regular binary file, we are done.
+	if (mtfile(mtname) == NO) {
+	    call sfree (sp)
+	    return (open (mtname, acmode, BINARY_FILE))
+	}
+
+	# Get mtio file descriptor slot, but do not allocate it until
+	# we are ready to open the file.
+
+	for (mt=1;  mt <= MT_MAXTAPES && MT_OSCHAN(mt) != NULL;  mt=mt+1)
+	    ;
+	if (mt > MT_MAXTAPES)
+	    call syserrs (SYS_MTMULTOPEN, mtname)
+
+	# Break mtname into drive name, file and record number, etc.
+	call mtparse (mtname, MT_DEVICE(mt), SZ_DEVICE, 
+	    new_file, new_record, Memc[devcap], SZ_DEVCAP)
+	if (new_record == ERR)
+	    new_record = 1
+
+	# Get tapecap info.
+	gty = mt_gtyopen (MT_DEVICE(mt), Memc[devcap])
+	MT_DEVCAP(mt) = gtycaps (gty)
+	if (gtygets (gty, "dv", MT_IODEV(mt), SZ_IODEV) <= 0) {
+	    call eprintf ("missing `dv' parameter in tapecap entry for %s\n")
+		call pargstr (mtname)
+	    call syserrs (SYS_MTTAPECAP, mtname)
+	}
+	call ki_xnode (MT_DEVICE(mt), MT_IODEV(mt), SZ_IODEV)
+
+	# If the device has not been allocated, at least write out the
+	# lock file.  This will not physically allocate the device, but
+	# the lock file is required to be able to access the device.
+
+	call mt_glock (mtname, MT_LKNAME(mt), SZ_LKNAME)
+	if (mt_devallocated (MT_IODEV(mt)) == NO)
+	    if (access (MT_LKNAME(mt), 0,0) == NO)
+		call mtallocate (mtname)
+
+	# Get current tape position.
+	call mt_getpos (mtname, mt)
+
+	MT_FILE(mt) = new_file
+	MT_RECORD(mt) = new_record
+	MT_ATEOF(mt) = NO
+
+	# If tape is opened for writing but no file number is given, default
+	# to EOT.  Defaulting to current file or BOT could result in
+	# destruction of the tape.  Note that this default WILL RESULT IN TAPE
+	# RUNAWAY if used on a blank tape.  Blank tapes must be explicitly
+	# written at file [1], or opened with access mode NEW_TAPE.
+
+	if ((acmode == WRITE_ONLY && MT_FILE(mt) == -1) || (acmode == APPEND)) {
+	    MT_FILE(mt) = EOT
+	    MT_RECORD(mt) = 1
+	} else if (acmode == NEW_TAPE) {
+	    MT_FILE(mt) = 1
+	    MT_RECORD(mt) = 1
+	}
+
+	# Make sure that we are not reopening a drive which is already open.
+	for (fd=1;  fd <= MT_MAXTAPES;  fd=fd+1)
+	    if (fd != mt && MT_OSCHAN(fd) != NULL)
+		if (streq (MT_DEVICE(fd), MT_DEVICE(mt)))
+		    call syserrs (SYS_MTMULTOPEN, mtname)
+
+	# Initialize the remaining fields in the file descriptor and open the
+	# device.  ZOPNMT will position the tape.  Note that we pass the index
+	# of the new mtio descriptor slot to ZOPNMT in the common.  This is a
+	# bit ugly, but is safe enough, since we know that FOPNBF is going to
+	# call ZOPNMT.
+
+	switch (acmode) {
+	case READ_ONLY:
+	    MT_ACMODE(mt) = READ_ONLY
+	case WRITE_ONLY, APPEND, NEW_TAPE:
+	    MT_ACMODE(mt) = WRITE_ONLY
+	default:
+	    call syserrs (SYS_MTACMODE, mtname)
+	}
+
+	new_mtchan = mt
+	fd = fopnbf (MT_IODEV(mt), acmode,
+	    zopnmt, zardmt, zawrmt, zawtmt, zsttmt, zclsmt)
+
+	# Set the file buffer size (record size for variable block devices).
+	if (bufsize > 0)
+	    call fseti (fd, F_BUFSIZE, bufsize)
+	
+	# If the user specified a record offset, skip records up to there.
+	# Zero means leave positioned to old record.
+
+	if (MT_RECORD(mt) == 0)
+	    MT_RECORD(mt) = MT_RECNO(mt)
+	if (MT_RECORD(mt) > 1) {
+	    nskip = MT_RECORD(mt) - 1
+	    MT_RECORD(mt) = 1
+	    if (mt_skip_record (fd, nskip) != nskip)
+		call syserrs (SYS_MTSKIPREC, mtname)
+	}
+
+	call mt_savepos (mt)
+
+	call sfree (sp)
+	return (fd)
+end