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Borislav Petkov
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Bartlomiej Zolnierkiewicz
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| refs/heads/master: 10569713c78f3c499745651aebc90b0d1c454c28 |
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| /* | ||
| * 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. | ||
| * | ||
| * 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! | ||
| * | ||
| * 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. | ||
| */ | ||
| 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. | ||
|
|
||
| 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! | ||
|
|
||
| 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. |