ftape-rw.c

linux-2.6.15.6

	int expected = 0;
	int count = 1;
	int short_seek;
	int target = segment_id - margin;
	TRACE_FUN(ft_t_flow);

	if (ft_location.known && !validate(segment_id)) {
		ftape_sleep(1 * FT_SECOND);
		ft_failure = 1;
		TRACE_ABORT(-EIO, ft_t_err,
			    "fatal: head off track (bad hardware?)");
	}
	do {
		if (!ft_location.known) {
			TRACE(ft_t_warn, "warning: location not known");
		}
		TRACE(ft_t_noise, "from %d/%d to %d/0 - %d",
		      ft_location.segment, ft_location.sector,
		      segment_id, margin);
		/*  min_rewind == 1 + overshoot_when_doing_minimum_rewind
		 *  overshoot  == overshoot_when_doing_larger_rewind
		 *  Initially min_rewind == 1 + overshoot, optimization
		 *  of both values will be done separately.
		 *  overshoot and min_rewind can be negative as both are
		 *  sums of three components:
		 *  any_overshoot == rewind_overshoot - 
		 *                   stop_overshoot   -
		 *                   start_overshoot
		 */
		if (ft_location.segment - target - (min_rewind - 1) < 1) {
			short_seek = 1;
		} else {
			count = ft_location.segment - target - overshoot;
			short_seek = (count < 1);
		}
		if (short_seek) {
			count = 1;	/* do shortest rewind */
			expected = ft_location.segment - min_rewind;
			if (expected/ft_segments_per_track != ft_location.track) {
				expected = (ft_location.track * 
					    ft_segments_per_track);
			}
		} else {
			expected = target;
		}
		fast_seek(count, 1);
		logical_forward();
		if (ftape_read_id() < 0 || !ft_location.known ||
		    (sigtestsetmask(&current->pending.signal, _DONT_BLOCK))) {
			if ((!ftape_tape_running && !ft_location.known) ||
			    ++failures > FT_SECTORS_PER_SEGMENT) {
				TRACE_ABORT(-EIO, ft_t_err,
					    "read_id failed completely");
			}
			FT_SIGNAL_EXIT(_DONT_BLOCK);
			TRACE_CATCH(ftape_report_drive_status(pstatus),);
			TRACE(ft_t_noise, "ftape_read_id failed, retry (%d)",
			      failures);
			continue;
		}
		TRACE(ft_t_noise, "ended at %d/%d (%d,%d,%d)", 
		      ft_location.segment, ft_location.sector,
		      min_rewind, overshoot, inhibit_correction);
		if (!inhibit_correction &&
		    (ft_location.segment < expected ||
		     ft_location.segment > expected + margin)) {
			int error = expected - ft_location.segment;
			if (short_seek) {
				TRACE(ft_t_noise,
				      "adjusting min_rewind from %d to %d",
				      min_rewind, min_rewind + error);
				min_rewind += error;
				if (min_rewind < -5) {
					/* is this right ? FIXME ! */
					/* keep sane value */
					min_rewind = -5;
					TRACE(ft_t_noise, 
					      "clipped min_rewind to %d",
					      min_rewind);
				}
			} else {
				TRACE(ft_t_noise,
				      "adjusting overshoot from %d to %d",
				      overshoot, overshoot + error);
				overshoot += error;
				if (overshoot < -5 ||
				    overshoot > OVERSHOOT_LIMIT) {
					if (overshoot < 0) {
						/* keep sane value */
						overshoot = -5;
					} else {
						/* keep sane value */
						overshoot = OVERSHOOT_LIMIT;
					}
					TRACE(ft_t_noise,
					      "clipped overshoot to %d",
					      overshoot);
				}
			}
		}
	} while (ft_location.segment > segment_id);
	if (ft_location.known) {
		TRACE(ft_t_noise, "current location: %d/%d",
		      ft_location.segment, ft_location.sector);
	}
	TRACE_EXIT 0;
}

static int determine_position(void)
{
	int retry = 0;
	int status;
	int result;
	TRACE_FUN(ft_t_flow);

	if (!ftape_tape_running) {
		/*  This should only happen if tape is stopped by isr.
		 */
		TRACE(ft_t_flow, "waiting for tape stop");
		if (ftape_ready_wait(ftape_timeout.pause, &status) < 0) {
			TRACE(ft_t_flow, "drive still running (fatal)");
			ftape_tape_running = 1;	/* ? */
		}
	} else {
		ftape_report_drive_status(&status);
	}
	if (status & QIC_STATUS_READY) {
		/*  Drive must be ready to check error state !
		 */
		TRACE(ft_t_flow, "drive is ready");
		if (status & QIC_STATUS_ERROR) {
			unsigned int error;
			qic117_cmd_t command;

			/*  Report and clear error state, try to continue.
			 */
			TRACE(ft_t_flow, "error status set");
			ftape_report_error(&error, &command, 1);
			ftape_ready_wait(ftape_timeout.reset, &status);
			ftape_tape_running = 0;	/* ? */
		}
		if (check_bot_eot(status)) {
			if (ft_location.bot) {
				if ((status & QIC_STATUS_READY) == 0) {
					/* tape moving away from
					 * bot/eot, let's see if we
					 * can catch up with the first
					 * segment on this track.
					 */
				} else {
					TRACE(ft_t_flow,
					      "start tape from logical bot");
					logical_forward();	/* start moving */
				}
			} else {
				if ((status & QIC_STATUS_READY) == 0) {
					TRACE(ft_t_noise, "waiting for logical end of track");
					result = ftape_ready_wait(ftape_timeout.reset, &status);
					/* error handling needed ? */
				} else {
					TRACE(ft_t_noise,
					      "tape at logical end of track");
				}
			}
		} else {
			TRACE(ft_t_flow, "start tape");
			logical_forward();	/* start moving */
			ft_location.known = 0;	/* not cleared by logical forward ! */
		}
	}
	/* tape should be moving now, start reading id's
	 */
	while (!ft_location.known &&
	       retry++ < FT_SECTORS_PER_SEGMENT &&
	       (result = ftape_read_id()) < 0) {

		TRACE(ft_t_flow, "location unknown");

		/* exit on signal
		 */
		FT_SIGNAL_EXIT(_DONT_BLOCK);

		/*  read-id somehow failed, tape may
		 *  have reached end or some other
		 *  error happened.
		 */
		TRACE(ft_t_flow, "read-id failed");
		TRACE_CATCH(ftape_report_drive_status(&status),);
		TRACE(ft_t_err, "ftape_report_drive_status: 0x%02x", status);
		if (status & QIC_STATUS_READY) {
			ftape_tape_running = 0;
			TRACE(ft_t_noise, "tape stopped for unknown reason! "
			      "status = 0x%02x", status);
			if (status & QIC_STATUS_ERROR ||
			    !check_bot_eot(status)) {
				/* oops, tape stopped but not at end!
				 */
				TRACE_EXIT -EIO;
			}
		}
	}
	TRACE(ft_t_flow,
	      "tape is positioned at segment %d", ft_location.segment);
	TRACE_EXIT ft_location.known ? 0 : -EIO;
}

/*      Get the tape running and position it just before the
 *      requested segment.
 *      Seek tape-track and reposition as needed.
 */
int ftape_start_tape(int segment_id, int sector_offset)
{
	int track = segment_id / ft_segments_per_track;
	int result = -EIO;
	int status;
	static int last_segment = -1;
	static int bad_bus_timing = 0;
	/* number of segments passing the head between starting the tape
	 * and being able to access the first sector.
	 */
	static int start_offset = 1;
	int retry;
	TRACE_FUN(ft_t_flow);

	/* If sector_offset > 0, seek into wanted segment instead of
	 * into previous.
	 * This allows error recovery if a part of the segment is bad
	 * (erased) causing the tape drive to generate an index pulse
	 * thus causing a no-data error before the requested sector
	 * is reached.
	 */
	ftape_tape_running = 0;
	TRACE(ft_t_noise, "target segment: %d/%d%s", segment_id, sector_offset,
		ft_buffer[ft_head]->retry > 0 ? " retry" : "");
	if (ft_buffer[ft_head]->retry > 0) {	/* this is a retry */
		int dist = segment_id - last_segment;

		if ((int)ft_history.overrun_errors < overrun_count_offset) {
			overrun_count_offset = ft_history.overrun_errors;
		} else if (dist < 0 || dist > 50) {
			overrun_count_offset = ft_history.overrun_errors;
		} else if ((ft_history.overrun_errors -
			    overrun_count_offset) >= 8) {
			if (ftape_increase_threshold() >= 0) {
				--ft_buffer[ft_head]->retry;
				overrun_count_offset =
					ft_history.overrun_errors;
				TRACE(ft_t_warn, "increased threshold because "
				      "of excessive overrun errors");
			} else if (!bad_bus_timing && ft_data_rate >= 1000) {
				ftape_half_data_rate();
				--ft_buffer[ft_head]->retry;
				bad_bus_timing = 1;
				overrun_count_offset =
					ft_history.overrun_errors;
				TRACE(ft_t_warn, "reduced datarate because "
				      "of excessive overrun errors");
			}
		}
	}
	last_segment = segment_id;
	if (ft_location.track != track ||
	    (ftape_might_be_off_track && ft_buffer[ft_head]->retry== 0)) {
		/* current track unknown or not equal to destination
		 */
		ftape_ready_wait(ftape_timeout.seek, &status);
		ftape_seek_head_to_track(track);
		/* overrun_count_offset = ft_history.overrun_errors; */
	}
	result = -EIO;
	retry = 0;
	while (result < 0     &&
	       retry++ <= 5   &&
	       !ft_failure &&
	       !(sigtestsetmask(&current->pending.signal, _DONT_BLOCK))) {
		
		if (retry && start_offset < 5) {
			start_offset ++;
		}
		/*  Check if we are able to catch the requested
		 *  segment in time.
		 */
		if ((ft_location.known || (determine_position() == 0)) &&
		    ft_location.segment >=
		    (segment_id -
		     ((ftape_tape_running || ft_location.bot)
		      ? 0 : start_offset))) {
			/*  Too far ahead (in or past target segment).
			 */
			if (ftape_tape_running) {
				if ((result = ftape_stop_tape(&status)) < 0) {
					TRACE(ft_t_err,
					      "stop tape failed with code %d",
					      result);
					break;
				}
				TRACE(ft_t_noise, "tape stopped");
				ftape_tape_running = 0;
			}
			TRACE(ft_t_noise, "repositioning");
			++ft_history.rewinds;
			if (segment_id % ft_segments_per_track < start_offset){
				TRACE(ft_t_noise, "end of track condition\n"
				      KERN_INFO "segment_id        : %d\n"
				      KERN_INFO "ft_segments_per_track: %d\n"
				      KERN_INFO "start_offset      : %d",
				      segment_id, ft_segments_per_track, 
				      start_offset);
				      
				/*  If seeking to first segments on
				 *  track better do a complete rewind
				 *  to logical begin of track to get a
				 *  more steady tape motion.  
				 */
				result = ftape_command_wait(
					(ft_location.track & 1)
					? QIC_PHYSICAL_FORWARD
					: QIC_PHYSICAL_REVERSE,
					ftape_timeout.rewind, &status);
				check_bot_eot(status);	/* update location */
			} else {
				result= skip_reverse(segment_id - start_offset,
						     &status);
			}
		}
		if (!ft_location.known) {
			TRACE(ft_t_bug, "panic: location not known");
			result = -EIO;
			continue; /* while() will check for failure */
		}
		TRACE(ft_t_noise, "current segment: %d/%d",
		      ft_location.segment, ft_location.sector);
		/*  We're on the right track somewhere before the
		 *  wanted segment.  Start tape movement if needed and
		 *  skip to just before or inside the requested
		 *  segment. Keep tape running.  
		 */
		result = 0;
		if (ft_location.segment < 
		    (segment_id - ((ftape_tape_running || ft_location.bot)
				   ? 0 : start_offset))) {
			if (sector_offset > 0) {
				result = seek_forward(segment_id,
						      retry <= 3);
			} else {
				result = seek_forward(segment_id - 1,
						      retry <= 3);
			}
		}
		if (result == 0 &&
		    ft_location.segment !=
		    (segment_id - (sector_offset > 0 ? 0 : 1))) {
			result = -EIO;
		}
	}
	if (result < 0) {
		TRACE(ft_t_err, "failed to reposition");
	} else {
		ft_runner_status = running;
	}
	TRACE_EXIT result;
}