Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!hplabs!hpfcso!hpfcdc!paulp
From: paulp@hpfcdc.HP.COM (Paul Perlmutter)
Newsgroups: comp.sys.hp
Subject: Re: Reading past end-of-tape mark on cartridge tape?
Message-ID: <5570382@hpfcdc.HP.COM>
Date: 1 Mar 90 21:30:52 GMT
References: <483@limbo.Intuitive.Com>
Organization: HP Ft. Collins, Co.
Lines: 53



I have a couple of questions:

	- What does the kernel message buffer indicate.  If it
	  is reading and EOF,  then the driver will log this
	  in the buffer.

	- If it is an EOF mark,  what is it doing there, and
	  how do want to copy it?  (e.g. skip it, or reproduce
	  it on the disk as a block of all 0's?)

Two options in any case are available, each with tradeoffs:
(assuming it is a tape mark)

	(1) use 'tcio' - this can be achieved with an option:
		-f  n
	    where n indicates number of tape marks to skip.
	    Thus, by clever repeated use of 'tcio',  you
	    can read the entire tape.

	(2) write your own program:  this is perhaps the more
	    time consuming,  but at least you'll have control
	    of what's going on.  Essentially,  you will copy
	    the tape - even on error, copying a block of zeroes
	    when an error or tape mark is encountered.  Here is 
	    the critical loop:

		char zerobuf[1K];

		main()
		{
		char *ptr, buf[1K];

		for (i=0; i<tape_size_in_blks; i++)	{
			ptr = zerobuf;	/* Null buffer */
			if ((ret = read(fd9144, buf, 1K)) == 1K)
				ptr = buf;
			if ((ret = write(fd_disk, ptr, 1k)) != 1K)
				perror("error in write"), exit(1);
			}
		}
				
	   Use diskinfo -b to determine tape size in blocks.
	   
>	%  tcio -ivZ /dev/rct
>	tape size: 65408 blocks
>	tcio(1009): 1024 byte blocks read: 96

A tape (hard) error may be causing the tape to bomb out too!

Cheers, 
Paul Perlmutter