Commit 5ce78af4 authored by Borislav Petkov's avatar Borislav Petkov Committed by Bartlomiej Zolnierkiewicz

ide-tape: move historical changelog to Documentation/ide/ChangeLog.ide-tape.1995-2002

Also, cleanup whitespace and update comments.

Bart:
- remove reference to drivers/block/ide.c
- move driver documentation to Documentation/ide/ide-tape.txt
Signed-off-by: default avatarBorislav Petkov <bbpetkov@yahoo.de>
Signed-off-by: default avatarBartlomiej Zolnierkiewicz <bzolnier@gmail.com>
parent dcb425f5
/*
* Ver 0.1 Nov 1 95 Pre-working code :-)
* Ver 0.2 Nov 23 95 A short backup (few megabytes) and restore procedure
* was successful ! (Using tar cvf ... on the block
* device interface).
* A longer backup resulted in major swapping, bad
* overall Linux performance and eventually failed as
* we received non serial read-ahead requests from the
* buffer cache.
* Ver 0.3 Nov 28 95 Long backups are now possible, thanks to the
* character device interface. Linux's responsiveness
* and performance doesn't seem to be much affected
* from the background backup procedure.
* Some general mtio.h magnetic tape operations are
* now supported by our character device. As a result,
* popular tape utilities are starting to work with
* ide tapes :-)
* The following configurations were tested:
* 1. An IDE ATAPI TAPE shares the same interface
* and irq with an IDE ATAPI CDROM.
* 2. An IDE ATAPI TAPE shares the same interface
* and irq with a normal IDE disk.
* Both configurations seemed to work just fine !
* However, to be on the safe side, it is meanwhile
* recommended to give the IDE TAPE its own interface
* and irq.
* The one thing which needs to be done here is to
* add a "request postpone" feature to ide.c,
* so that we won't have to wait for the tape to finish
* performing a long media access (DSC) request (such
* as a rewind) before we can access the other device
* on the same interface. This effect doesn't disturb
* normal operation most of the time because read/write
* requests are relatively fast, and once we are
* performing one tape r/w request, a lot of requests
* from the other device can be queued and ide.c will
* service all of them after this single tape request.
* Ver 1.0 Dec 11 95 Integrated into Linux 1.3.46 development tree.
* On each read / write request, we now ask the drive
* if we can transfer a constant number of bytes
* (a parameter of the drive) only to its buffers,
* without causing actual media access. If we can't,
* we just wait until we can by polling the DSC bit.
* This ensures that while we are not transferring
* more bytes than the constant referred to above, the
* interrupt latency will not become too high and
* we won't cause an interrupt timeout, as happened
* occasionally in the previous version.
* While polling for DSC, the current request is
* postponed and ide.c is free to handle requests from
* the other device. This is handled transparently to
* ide.c. The hwgroup locking method which was used
* in the previous version was removed.
* Use of new general features which are provided by
* ide.c for use with atapi devices.
* (Programming done by Mark Lord)
* Few potential bug fixes (Again, suggested by Mark)
* Single character device data transfers are now
* not limited in size, as they were before.
* We are asking the tape about its recommended
* transfer unit and send a larger data transfer
* as several transfers of the above size.
* For best results, use an integral number of this
* basic unit (which is shown during driver
* initialization). I will soon add an ioctl to get
* this important parameter.
* Our data transfer buffer is allocated on startup,
* rather than before each data transfer. This should
* ensure that we will indeed have a data buffer.
* Ver 1.1 Dec 14 95 Fixed random problems which occurred when the tape
* shared an interface with another device.
* (poll_for_dsc was a complete mess).
* Removed some old (non-active) code which had
* to do with supporting buffer cache originated
* requests.
* The block device interface can now be opened, so
* that general ide driver features like the unmask
* interrupts flag can be selected with an ioctl.
* This is the only use of the block device interface.
* New fast pipelined operation mode (currently only on
* writes). When using the pipelined mode, the
* throughput can potentially reach the maximum
* tape supported throughput, regardless of the
* user backup program. On my tape drive, it sometimes
* boosted performance by a factor of 2. Pipelined
* mode is enabled by default, but since it has a few
* downfalls as well, you may want to disable it.
* A short explanation of the pipelined operation mode
* is available below.
* Ver 1.2 Jan 1 96 Eliminated pipelined mode race condition.
* Added pipeline read mode. As a result, restores
* are now as fast as backups.
* Optimized shared interface behavior. The new behavior
* typically results in better IDE bus efficiency and
* higher tape throughput.
* Pre-calculation of the expected read/write request
* service time, based on the tape's parameters. In
* the pipelined operation mode, this allows us to
* adjust our polling frequency to a much lower value,
* and thus to dramatically reduce our load on Linux,
* without any decrease in performance.
* Implemented additional mtio.h operations.
* The recommended user block size is returned by
* the MTIOCGET ioctl.
* Additional minor changes.
* Ver 1.3 Feb 9 96 Fixed pipelined read mode bug which prevented the
* use of some block sizes during a restore procedure.
* The character device interface will now present a
* continuous view of the media - any mix of block sizes
* during a backup/restore procedure is supported. The
* driver will buffer the requests internally and
* convert them to the tape's recommended transfer
* unit, making performance almost independent of the
* chosen user block size.
* Some improvements in error recovery.
* By cooperating with ide-dma.c, bus mastering DMA can
* now sometimes be used with IDE tape drives as well.
* Bus mastering DMA has the potential to dramatically
* reduce the CPU's overhead when accessing the device,
* and can be enabled by using hdparm -d1 on the tape's
* block device interface. For more info, read the
* comments in ide-dma.c.
* Ver 1.4 Mar 13 96 Fixed serialize support.
* Ver 1.5 Apr 12 96 Fixed shared interface operation, broken in 1.3.85.
* Fixed pipelined read mode inefficiency.
* Fixed nasty null dereferencing bug.
* Ver 1.6 Aug 16 96 Fixed FPU usage in the driver.
* Fixed end of media bug.
* Ver 1.7 Sep 10 96 Minor changes for the CONNER CTT8000-A model.
* Ver 1.8 Sep 26 96 Attempt to find a better balance between good
* interactive response and high system throughput.
* Ver 1.9 Nov 5 96 Automatically cross encountered filemarks rather
* than requiring an explicit FSF command.
* Abort pending requests at end of media.
* MTTELL was sometimes returning incorrect results.
* Return the real block size in the MTIOCGET ioctl.
* Some error recovery bug fixes.
* Ver 1.10 Nov 5 96 Major reorganization.
* Reduced CPU overhead a bit by eliminating internal
* bounce buffers.
* Added module support.
* Added multiple tape drives support.
* Added partition support.
* Rewrote DSC handling.
* Some portability fixes.
* Removed ide-tape.h.
* Additional minor changes.
* Ver 1.11 Dec 2 96 Bug fix in previous DSC timeout handling.
* Use ide_stall_queue() for DSC overlap.
* Use the maximum speed rather than the current speed
* to compute the request service time.
* Ver 1.12 Dec 7 97 Fix random memory overwriting and/or last block data
* corruption, which could occur if the total number
* of bytes written to the tape was not an integral
* number of tape blocks.
* Add support for INTERRUPT DRQ devices.
* Ver 1.13 Jan 2 98 Add "speed == 0" work-around for HP COLORADO 5GB
* Ver 1.14 Dec 30 98 Partial fixes for the Sony/AIWA tape drives.
* Replace cli()/sti() with hwgroup spinlocks.
* Ver 1.15 Mar 25 99 Fix SMP race condition by replacing hwgroup
* spinlock with private per-tape spinlock.
* Ver 1.16 Sep 1 99 Add OnStream tape support.
* Abort read pipeline on EOD.
* Wait for the tape to become ready in case it returns
* "in the process of becoming ready" on open().
* Fix zero padding of the last written block in
* case the tape block size is larger than PAGE_SIZE.
* Decrease the default disconnection time to tn.
* Ver 1.16e Oct 3 99 Minor fixes.
* Ver 1.16e1 Oct 13 99 Patches by Arnold Niessen,
* niessen@iae.nl / arnold.niessen@philips.com
* GO-1) Undefined code in idetape_read_position
* according to Gadi's email
* AJN-1) Minor fix asc == 11 should be asc == 0x11
* in idetape_issue_packet_command (did effect
* debugging output only)
* AJN-2) Added more debugging output, and
* added ide-tape: where missing. I would also
* like to add tape->name where possible
* AJN-3) Added different debug_level's
* via /proc/ide/hdc/settings
* "debug_level" determines amount of debugging output;
* can be changed using /proc/ide/hdx/settings
* 0 : almost no debugging output
* 1 : 0+output errors only
* 2 : 1+output all sensekey/asc
* 3 : 2+follow all chrdev related procedures
* 4 : 3+follow all procedures
* 5 : 4+include pc_stack rq_stack info
* 6 : 5+USE_COUNT updates
* AJN-4) Fixed timeout for retension in idetape_queue_pc_tail
* from 5 to 10 minutes
* AJN-5) Changed maximum number of blocks to skip when
* reading tapes with multiple consecutive write
* errors from 100 to 1000 in idetape_get_logical_blk
* Proposed changes to code:
* 1) output "logical_blk_num" via /proc
* 2) output "current_operation" via /proc
* 3) Either solve or document the fact that `mt rewind' is
* required after reading from /dev/nhtx to be
* able to rmmod the idetape module;
* Also, sometimes an application finishes but the
* device remains `busy' for some time. Same cause ?
* Proposed changes to release-notes:
* 4) write a simple `quickstart' section in the
* release notes; I volunteer if you don't want to
* 5) include a pointer to video4linux in the doc
* to stimulate video applications
* 6) release notes lines 331 and 362: explain what happens
* if the application data rate is higher than 1100 KB/s;
* similar approach to lower-than-500 kB/s ?
* 7) 6.6 Comparison; wouldn't it be better to allow different
* strategies for read and write ?
* Wouldn't it be better to control the tape buffer
* contents instead of the bandwidth ?
* 8) line 536: replace will by would (if I understand
* this section correctly, a hypothetical and unwanted situation
* is being described)
* Ver 1.16f Dec 15 99 Change place of the secondary OnStream header frames.
* Ver 1.17 Nov 2000 / Jan 2001 Marcel Mol, marcel@mesa.nl
* - Add idetape_onstream_mode_sense_tape_parameter_page
* function to get tape capacity in frames: tape->capacity.
* - Add support for DI-50 drives( or any DI- drive).
* - 'workaround' for read error/blank block around block 3000.
* - Implement Early warning for end of media for Onstream.
* - Cosmetic code changes for readability.
* - Idetape_position_tape should not use SKIP bit during
* Onstream read recovery.
* - Add capacity, logical_blk_num and first/last_frame_position
* to /proc/ide/hd?/settings.
* - Module use count was gone in the Linux 2.4 driver.
* Ver 1.17a Apr 2001 Willem Riede osst@riede.org
* - Get drive's actual block size from mode sense block descriptor
* - Limit size of pipeline
* Ver 1.17b Oct 2002 Alan Stern <stern@rowland.harvard.edu>
* Changed IDETAPE_MIN_PIPELINE_STAGES to 1 and actually used
* it in the code!
* Actually removed aborted stages in idetape_abort_pipeline
* instead of just changing the command code.
* Made the transfer byte count for Request Sense equal to the
* actual length of the data transfer.
* Changed handling of partial data transfers: they do not
* cause DMA errors.
* Moved initiation of DMA transfers to the correct place.
* Removed reference to unallocated memory.
* Made __idetape_discard_read_pipeline return the number of
* sectors skipped, not the number of stages.
* Replaced errant kfree() calls with __idetape_kfree_stage().
* Fixed off-by-one error in testing the pipeline length.
* Fixed handling of filemarks in the read pipeline.
* Small code optimization for MTBSF and MTBSFM ioctls.
* Don't try to unlock the door during device close if is
* already unlocked!
* Cosmetic fixes to miscellaneous debugging output messages.
* Set the minimum /proc/ide/hd?/settings values for "pipeline",
* "pipeline_min", and "pipeline_max" to 1.
*/
/*
* IDE ATAPI streaming tape driver.
*
* This driver is a part of the Linux ide driver.
*
* The driver, in co-operation with ide.c, basically traverses the
* request-list for the block device interface. The character device
* interface, on the other hand, creates new requests, adds them
* to the request-list of the block device, and waits for their completion.
*
* Pipelined operation mode is now supported on both reads and writes.
*
* The block device major and minor numbers are determined from the
* tape's relative position in the ide interfaces, as explained in ide.c.
*
* The character device interface consists of the following devices:
*
* ht0 major 37, minor 0 first IDE tape, rewind on close.
* ht1 major 37, minor 1 second IDE tape, rewind on close.
* ...
* nht0 major 37, minor 128 first IDE tape, no rewind on close.
* nht1 major 37, minor 129 second IDE tape, no rewind on close.
* ...
*
* The general magnetic tape commands compatible interface, as defined by
* include/linux/mtio.h, is accessible through the character device.
*
* General ide driver configuration options, such as the interrupt-unmask
* flag, can be configured by issuing an ioctl to the block device interface,
* as any other ide device.
*
* Our own ide-tape ioctl's can be issued to either the block device or
* the character device interface.
*
* Maximal throughput with minimal bus load will usually be achieved in the
* following scenario:
*
* 1. ide-tape is operating in the pipelined operation mode.
* 2. No buffering is performed by the user backup program.
*
* Testing was done with a 2 GB CONNER CTMA 4000 IDE ATAPI Streaming Tape Drive.
*
* Here are some words from the first releases of hd.c, which are quoted
* in ide.c and apply here as well:
*
* | Special care is recommended. Have Fun!
*
*
* An overview of the pipelined operation mode.
*
* In the pipelined write mode, we will usually just add requests to our
* pipeline and return immediately, before we even start to service them. The
* user program will then have enough time to prepare the next request while
* we are still busy servicing previous requests. In the pipelined read mode,
* the situation is similar - we add read-ahead requests into the pipeline,
* before the user even requested them.
*
* The pipeline can be viewed as a "safety net" which will be activated when
* the system load is high and prevents the user backup program from keeping up
* with the current tape speed. At this point, the pipeline will get
* shorter and shorter but the tape will still be streaming at the same speed.
* Assuming we have enough pipeline stages, the system load will hopefully
* decrease before the pipeline is completely empty, and the backup program
* will be able to "catch up" and refill the pipeline again.
*
* When using the pipelined mode, it would be best to disable any type of
* buffering done by the user program, as ide-tape already provides all the
* benefits in the kernel, where it can be done in a more efficient way.
* As we will usually not block the user program on a request, the most
* efficient user code will then be a simple read-write-read-... cycle.
* Any additional logic will usually just slow down the backup process.
*
* Using the pipelined mode, I get a constant over 400 KBps throughput,
* which seems to be the maximum throughput supported by my tape.
*
* However, there are some downfalls:
*
* 1. We use memory (for data buffers) in proportional to the number
* of pipeline stages (each stage is about 26 KB with my tape).
* 2. In the pipelined write mode, we cheat and postpone error codes
* to the user task. In read mode, the actual tape position
* will be a bit further than the last requested block.
*
* Concerning (1):
*
* 1. We allocate stages dynamically only when we need them. When
* we don't need them, we don't consume additional memory. In
* case we can't allocate stages, we just manage without them
* (at the expense of decreased throughput) so when Linux is
* tight in memory, we will not pose additional difficulties.
*
* 2. The maximum number of stages (which is, in fact, the maximum
* amount of memory) which we allocate is limited by the compile
* time parameter IDETAPE_MAX_PIPELINE_STAGES.
*
* 3. The maximum number of stages is a controlled parameter - We
* don't start from the user defined maximum number of stages
* but from the lower IDETAPE_MIN_PIPELINE_STAGES (again, we
* will not even allocate this amount of stages if the user
* program can't handle the speed). We then implement a feedback
* loop which checks if the pipeline is empty, and if it is, we
* increase the maximum number of stages as necessary until we
* reach the optimum value which just manages to keep the tape
* busy with minimum allocated memory or until we reach
* IDETAPE_MAX_PIPELINE_STAGES.
*
* Concerning (2):
*
* In pipelined write mode, ide-tape can not return accurate error codes
* to the user program since we usually just add the request to the
* pipeline without waiting for it to be serviced. In case an error
* occurs, I will report it on the next user request.
*
* In the pipelined read mode, subsequent read requests or forward
* filemark spacing will perform correctly, as we preserve all blocks
* and filemarks which we encountered during our excess read-ahead.
*
* For accurate tape positioning and error reporting, disabling
* pipelined mode might be the best option.
*
* You can enable/disable/tune the pipelined operation mode by adjusting
* the compile time parameters below.
*
*
* Possible improvements.
*
* 1. Support for the ATAPI overlap protocol.
*
* In order to maximize bus throughput, we currently use the DSC
* overlap method which enables ide.c to service requests from the
* other device while the tape is busy executing a command. The
* DSC overlap method involves polling the tape's status register
* for the DSC bit, and servicing the other device while the tape
* isn't ready.
*
* In the current QIC development standard (December 1995),
* it is recommended that new tape drives will *in addition*
* implement the ATAPI overlap protocol, which is used for the
* same purpose - efficient use of the IDE bus, but is interrupt
* driven and thus has much less CPU overhead.
*
* ATAPI overlap is likely to be supported in most new ATAPI
* devices, including new ATAPI cdroms, and thus provides us
* a method by which we can achieve higher throughput when
* sharing a (fast) ATA-2 disk with any (slow) new ATAPI device.
*/
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