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From: dudek@endor.harvard.edu (Glen Dudek)
Newsgroups: comp.bugs.4bsd
Subject: tmscp tape drives give "hard error" on reading too small a record
Message-ID: <1681@husc6.UUCP>
Date: Thu, 16-Apr-87 12:58:39 EST
Article-I.D.: husc6.1681
Posted: Thu Apr 16 12:58:39 1987
Date-Received: Sun, 19-Apr-87 06:11:15 EST
Sender: news@husc6.UUCP
Reply-To: dudek@endor.UUCP (Glen Dudek)
Organization: Aiken Computation Lab Harvard, Cambridge, MA
Lines: 48
Keywords: tmscp, TU81, DEC

Index:	/usr/sys/vaxuba/tmscp.c 4.3BSD, Ultrix 1.2

Description:
	When reading a tape written with a blocksize larger than you are
	using to read, any tmscp tape drive (e.g., TU81, TK50) will die
	with a kernel printf "hard error: record data truncated" and an
	I/O error.  This should not be an error when using the raw device.

Repeat-By:
	Write a tape with a (reasonably) large blocksize, as in:
	    % tar cvfb /dev/rmt0 20 /etc/motd
	Use dd to read back the first 512 bytes of the first tape block:
	    % dd if=/dev/rmt0 of=/dev/null bs=512 count=1
	Watch the kernel barf.

Fix:
	Get DEC to stop using proprietary protocols which they cannot even
	write decent drivers for, or

	Change the following line in /usr/sys/vaxuba/tmscp.c:

*** /tmp/,RCSt1027293	Thu Apr 16 13:49:34 1987
--- tmscp.c	Thu Apr 16 13:35:05 1987
***************
*** 1548,1554 ****
  			{
  			if (mp->mscp_flags & M_EF_SEREX)
  				tms->tms_serex = 1;
! 			if (st != M_ST_TAPEM)
  				{
  				tprintf(tms->tms_ttyp,
  				    "tms%d: hard error bn%d\n",
--- 1548,1559 ----
  			{
  			if (mp->mscp_flags & M_EF_SEREX)
  				tms->tms_serex = 1;
! 			/* Truncated record on read of raw device is not
! 			 * an error -gd 4/16/87
! 			 */
! 			if (st != M_ST_TAPEM &&
! 			    !(st == M_ST_RDTRN && bp == &rtmsbuf[ui->ui_unit]
! 			    && (mp->mscp_opcode == (M_OP_READ|M_OP_END))))
  				{
  				tprintf(tms->tms_ttyp,
  				    "tms%d: hard error bn%d\n",
-----------
Glen Dudek				dudek@harvard.harvard.edu
Aiken Computation Lab			(617) 495-2871