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diff --git a/sys/mtio/zclsmt.x b/sys/mtio/zclsmt.x
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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<config.h>
+include	<knet.h>
+include	"mtio.h"
+
+# ZCLSMT -- Close a magtape file and device.  Update lockfile so that we
+# will know where the tape is positioned next time we open the device.
+# Deallocate the mtio descriptor so that it may be reused again.
+# 
+# We are being called during error recovery if "new_mtchan" is not null.
+# If MT_OSCHAN has also been set, then ZZOPMT was interrupted, probably while
+# trying to position the tape, and the position of the tape is indefinite.
+# Close the tape with acmode=read so that no tape marks are written, and write
+# the lockfile with file = -1 to signify that the position is indefinite.
+
+procedure zclsmt (mtchan, status)
+
+int	mtchan				#I i/o channel
+int	status				#O close status
+
+int	mt
+bool	error_recovery
+include	"mtio.com"
+
+begin
+	# Called by error recovery while positioning tape? (during open)
+	if (new_mtchan != NULL) {
+	    mt = new_mtchan
+	    if (MT_OSCHAN(mt) != NULL)
+		call zzclmt (MT_OSCHAN(mt), MT_DEVPOS(mt), status)
+
+	    call mt_savepos (mt)
+	    call mt_sync (ERR)
+	    new_mtchan = NULL
+
+	} else {
+	    mt = mtchan
+
+	    # If a task aborts while a tape file is open, mt_sync will
+	    # already have been called to update the position,
+	    # and the current file will have been set to undefined (-1).
+
+	    error_recovery = (MT_FILNO(mt) == -1)
+
+	    # Close device.  This clobbers MT_FILNO (see above).
+	    call zzclmt (MT_OSCHAN(mt), MT_DEVPOS(mt), status)
+
+	    # Update the tape position if not recovering from an abort.
+	    if (!error_recovery)
+		call mt_savepos (mt)
+	}
+
+	MT_OSCHAN(mt) = NULL
+end