program conlog

!++
!
!		CONLOG.BAS -- Read last n lines from 85xx console log
!
!	This program opens the 85xx console logfile (CSA3:[console]LOGFILE.DAT)
!	and extracts the last n lines (n is user supplied) of data from it.
!	The logfile is parsed to extract lines in a useful form for subsequent
!	analysis using a text editor or file viewing utility.
!
!	The logfile consists of a header block, and n (in this case 6000) data
!	blocks.  It is written to as a ring buffer, with context information 
!	held in the first few words of the header block.  Records in the buffer
!	are delimited by CR, LF pairs; in essence, an exact dump of what has 
!	appeared on the console terminal, although escape characters are 
!	converted to dollar signs.  
!
!	The program works by extracting the size of the file, current block
!	and offset within current block from the header block.  It then works
!	backward from the current position filling out a string array, most 
!	recent line first.  When the required number of lines have been 
!	extracted, the program reverses through the array, outputing the lines
!	in the correct order.
!
!	It appears that the contents of the last block and the header 
!	information don't always match; often there will be old data in the
!	output file.  This appears to be a problem with the header block being 
!	flushed to disk, but the data block remaining in memory on the Pro 350
!	console processor.  There seems to be little that can be done about 
!	this.
!
!	Note that for thie program to work, the console must be connect and the
!	Pro 350 hard disk mounted.  To do this, use:
!
!		$ MCR SYSGEN
!		SYSGEN>  CONNECT CONSOLE
!		SYSGEN>  EXIT
!		$ MOUNT/NOWRITE/SYSTEM CSA3: PROVOLUME
!
!	The /NOWRITE is very important.  Attempting to mount the console hard
!	disk for write will crash the system.  It should be mounted systemwide
!	immediately after connecting to prevent users from attemting to mount
!	it privately.  The console's floppy disks (CSA1: and CSA2:) are not 
!	affected by this, and can safely be left unmounted after connecting
!	the console.
!
!	Note also that the console directories on the Pro 350 are protected 
!	against user access; because of this, READALL privilege (or SYSPRV or
!	BYPASS) is necessary to use this program.
!
!	Author:	Don Stokes,			Phone: +64 4 496-5681
!		Government Printing Office,	   or: +64 4 737-320
!		Wellington, New Zealand.	  Fax: +64 4 734-943
!		Email: don@gp.govt.nz (work), don@zl2tnm.gp.govt.nz (home)
!		   or: PSI%(5301)47000028::DON
!	Date:	19-Aug-1990
!
!--

	option type = explicit

		!
		! Map the buffer for the console.
		! Lay out header data
		!
	map (logfile) word fill, blockmax, blockno, fill, fill, bytecount
	map (logfile) string text = 512
	map (logfile) string character(1 to 512) = 1

	declare long c,l, maxlines, cblk, mblk
	declare string outarray(10000), s, outfile

		!
		! Get user requirements:
		! 	Output file name, default is SYS$OUTPUT
		!	Number of lines to list, default is 24
		!
	set no prompt
	linput "Output file: "; outfile
	outfile = "SYS$OUTPUT:" if outfile = ""
	input "Lines to extract: "; maxlines
	maxlines = 24 if maxlines = 0
	maxlines = 10000 if maxlines > 10000

		!
		! Open files
		!
	open "CSA3:[console]LOGFILE.DAT" for input as file #1, 		       &
		access read, allow modify, 				       &
		organization sequential fixed, recordsize 512, 		       &
		recordtype any, map logfile
	open outfile for output as file #2, recordsize 32767, 		       &
		defaultname "LOGFILE.LIS"

		!
		! Get header record, extract current block, maximum block
		! and offset into current block
		!
	get #1
	cblk = blockno
	mblk = blockmax
	c = bytecount

		!
		! Get current block
		!
	get #1, record cblk

		!
		! Loop until we have all the lines we want
		!
	for l = 1 to maxlines

		!
		! If we have gone over a block boundary, get the next block 
		! from the logfile and restart the character pointer at the 
		! top of the block.
		! Read characters until we reach a line feed (CRs are ignored)
		! Add character to beginning of output line.
		!
		s = ""
	  loop:	while -1%
			if c < 1 then
				cblk = cblk - 1
				cblk = mblk if cblk = 1
				get #1, record cblk
				c = c + 512
			end if
			exit loop unless character(c) <> lf
			s = character(c) + s if character(c) >= " " 	       &
					     or character(c) = chr$(9)
			c = c - 1
		next

		!
		! Skip over linefeed and save string in array
		!
		c = c - 1
		outarray(l) = s
	next l

		!
		! Write the contents of the log array backwards into the 
		! output file (ends up in correct order).
		!
	print #2, outarray(l) for l = maxlines to 1 step -1

		!
		! Close files and exit
		!
	close #1
	close #2

	end program