410 lines
14 KiB
XML
410 lines
14 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
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<book id="scsimid">
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<bookinfo>
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<title>SCSI Interfaces Guide</title>
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<authorgroup>
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<author>
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<firstname>James</firstname>
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<surname>Bottomley</surname>
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<affiliation>
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<address>
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<email>James.Bottomley@hansenpartnership.com</email>
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</address>
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</affiliation>
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</author>
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<author>
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<firstname>Rob</firstname>
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<surname>Landley</surname>
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<affiliation>
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<address>
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<email>rob@landley.net</email>
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</address>
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</affiliation>
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</author>
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</authorgroup>
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<copyright>
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<year>2007</year>
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<holder>Linux Foundation</holder>
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</copyright>
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<legalnotice>
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<para>
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This documentation is free software; you can redistribute
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it and/or modify it under the terms of the GNU General Public
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License version 2.
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</para>
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<para>
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This program is distributed in the hope that it will be
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useful, but WITHOUT ANY WARRANTY; without even the implied
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warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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For more details see the file COPYING in the source
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distribution of Linux.
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</para>
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</legalnotice>
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</bookinfo>
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<toc></toc>
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<chapter id="intro">
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<title>Introduction</title>
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<sect1 id="protocol_vs_bus">
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<title>Protocol vs bus</title>
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<para>
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Once upon a time, the Small Computer Systems Interface defined both
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a parallel I/O bus and a data protocol to connect a wide variety of
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peripherals (disk drives, tape drives, modems, printers, scanners,
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optical drives, test equipment, and medical devices) to a host
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computer.
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</para>
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<para>
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Although the old parallel (fast/wide/ultra) SCSI bus has largely
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fallen out of use, the SCSI command set is more widely used than ever
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to communicate with devices over a number of different busses.
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</para>
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<para>
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The <ulink url='http://www.t10.org/scsi-3.htm'>SCSI protocol</ulink>
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is a big-endian peer-to-peer packet based protocol. SCSI commands
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are 6, 10, 12, or 16 bytes long, often followed by an associated data
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payload.
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</para>
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<para>
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SCSI commands can be transported over just about any kind of bus, and
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are the default protocol for storage devices attached to USB, SATA,
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SAS, Fibre Channel, FireWire, and ATAPI devices. SCSI packets are
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also commonly exchanged over Infiniband,
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<ulink url='http://i2o.shadowconnect.com/faq.php'>I20</ulink>, TCP/IP
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(<ulink url='http://en.wikipedia.org/wiki/ISCSI'>iSCSI</ulink>), even
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<ulink url='http://cyberelk.net/tim/parport/parscsi.html'>Parallel
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ports</ulink>.
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</para>
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</sect1>
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<sect1 id="subsystem_design">
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<title>Design of the Linux SCSI subsystem</title>
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<para>
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The SCSI subsystem uses a three layer design, with upper, mid, and low
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layers. Every operation involving the SCSI subsystem (such as reading
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a sector from a disk) uses one driver at each of the 3 levels: one
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upper layer driver, one lower layer driver, and the SCSI midlayer.
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</para>
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<para>
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The SCSI upper layer provides the interface between userspace and the
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kernel, in the form of block and char device nodes for I/O and
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ioctl(). The SCSI lower layer contains drivers for specific hardware
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devices.
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</para>
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<para>
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In between is the SCSI mid-layer, analogous to a network routing
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layer such as the IPv4 stack. The SCSI mid-layer routes a packet
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based data protocol between the upper layer's /dev nodes and the
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corresponding devices in the lower layer. It manages command queues,
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provides error handling and power management functions, and responds
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to ioctl() requests.
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</para>
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</sect1>
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</chapter>
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<chapter id="upper_layer">
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<title>SCSI upper layer</title>
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<para>
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The upper layer supports the user-kernel interface by providing
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device nodes.
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</para>
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<sect1 id="sd">
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<title>sd (SCSI Disk)</title>
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<para>sd (sd_mod.o)</para>
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<!-- !Idrivers/scsi/sd.c -->
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</sect1>
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<sect1 id="sr">
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<title>sr (SCSI CD-ROM)</title>
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<para>sr (sr_mod.o)</para>
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</sect1>
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<sect1 id="st">
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<title>st (SCSI Tape)</title>
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<para>st (st.o)</para>
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</sect1>
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<sect1 id="sg">
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<title>sg (SCSI Generic)</title>
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<para>sg (sg.o)</para>
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</sect1>
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<sect1 id="ch">
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<title>ch (SCSI Media Changer)</title>
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<para>ch (ch.c)</para>
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</sect1>
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</chapter>
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<chapter id="mid_layer">
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<title>SCSI mid layer</title>
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<sect1 id="midlayer_implementation">
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<title>SCSI midlayer implementation</title>
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<sect2 id="scsi_device.h">
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<title>include/scsi/scsi_device.h</title>
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<para>
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</para>
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!Iinclude/scsi/scsi_device.h
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</sect2>
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<sect2 id="scsi.c">
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<title>drivers/scsi/scsi.c</title>
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<para>Main file for the SCSI midlayer.</para>
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!Edrivers/scsi/scsi.c
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</sect2>
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<sect2 id="scsicam.c">
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<title>drivers/scsi/scsicam.c</title>
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<para>
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<ulink url='http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf'>SCSI
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Common Access Method</ulink> support functions, for use with
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HDIO_GETGEO, etc.
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</para>
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!Edrivers/scsi/scsicam.c
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</sect2>
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<sect2 id="scsi_error.c">
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<title>drivers/scsi/scsi_error.c</title>
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<para>Common SCSI error/timeout handling routines.</para>
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!Edrivers/scsi/scsi_error.c
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</sect2>
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<sect2 id="scsi_devinfo.c">
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<title>drivers/scsi/scsi_devinfo.c</title>
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<para>
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Manage scsi_dev_info_list, which tracks blacklisted and whitelisted
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devices.
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</para>
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!Idrivers/scsi/scsi_devinfo.c
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</sect2>
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<sect2 id="scsi_ioctl.c">
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<title>drivers/scsi/scsi_ioctl.c</title>
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<para>
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Handle ioctl() calls for SCSI devices.
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</para>
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!Edrivers/scsi/scsi_ioctl.c
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</sect2>
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<sect2 id="scsi_lib.c">
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<title>drivers/scsi/scsi_lib.c</title>
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<para>
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SCSI queuing library.
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</para>
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!Edrivers/scsi/scsi_lib.c
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</sect2>
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<sect2 id="scsi_lib_dma.c">
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<title>drivers/scsi/scsi_lib_dma.c</title>
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<para>
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SCSI library functions depending on DMA
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(map and unmap scatter-gather lists).
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</para>
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!Edrivers/scsi/scsi_lib_dma.c
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</sect2>
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<sect2 id="scsi_module.c">
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<title>drivers/scsi/scsi_module.c</title>
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<para>
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The file drivers/scsi/scsi_module.c contains legacy support for
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old-style host templates. It should never be used by any new driver.
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</para>
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</sect2>
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<sect2 id="scsi_proc.c">
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<title>drivers/scsi/scsi_proc.c</title>
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<para>
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The functions in this file provide an interface between
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the PROC file system and the SCSI device drivers
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It is mainly used for debugging, statistics and to pass
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information directly to the lowlevel driver.
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I.E. plumbing to manage /proc/scsi/*
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</para>
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!Idrivers/scsi/scsi_proc.c
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</sect2>
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<sect2 id="scsi_netlink.c">
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<title>drivers/scsi/scsi_netlink.c</title>
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<para>
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Infrastructure to provide async events from transports to userspace
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via netlink, using a single NETLINK_SCSITRANSPORT protocol for all
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transports.
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See <ulink url='http://marc.info/?l=linux-scsi&m=115507374832500&w=2'>the
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original patch submission</ulink> for more details.
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</para>
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!Idrivers/scsi/scsi_netlink.c
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</sect2>
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<sect2 id="scsi_scan.c">
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<title>drivers/scsi/scsi_scan.c</title>
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<para>
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Scan a host to determine which (if any) devices are attached.
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The general scanning/probing algorithm is as follows, exceptions are
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made to it depending on device specific flags, compilation options,
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and global variable (boot or module load time) settings.
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A specific LUN is scanned via an INQUIRY command; if the LUN has a
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device attached, a scsi_device is allocated and setup for it.
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For every id of every channel on the given host, start by scanning
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LUN 0. Skip hosts that don't respond at all to a scan of LUN 0.
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Otherwise, if LUN 0 has a device attached, allocate and setup a
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scsi_device for it. If target is SCSI-3 or up, issue a REPORT LUN,
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and scan all of the LUNs returned by the REPORT LUN; else,
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sequentially scan LUNs up until some maximum is reached, or a LUN is
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seen that cannot have a device attached to it.
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</para>
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!Idrivers/scsi/scsi_scan.c
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</sect2>
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<sect2 id="scsi_sysctl.c">
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<title>drivers/scsi/scsi_sysctl.c</title>
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<para>
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Set up the sysctl entry: "/dev/scsi/logging_level"
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(DEV_SCSI_LOGGING_LEVEL) which sets/returns scsi_logging_level.
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</para>
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</sect2>
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<sect2 id="scsi_sysfs.c">
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<title>drivers/scsi/scsi_sysfs.c</title>
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<para>
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SCSI sysfs interface routines.
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</para>
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!Edrivers/scsi/scsi_sysfs.c
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</sect2>
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<sect2 id="hosts.c">
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<title>drivers/scsi/hosts.c</title>
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<para>
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mid to lowlevel SCSI driver interface
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</para>
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!Edrivers/scsi/hosts.c
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</sect2>
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<sect2 id="constants.c">
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<title>drivers/scsi/constants.c</title>
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<para>
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mid to lowlevel SCSI driver interface
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</para>
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!Edrivers/scsi/constants.c
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</sect2>
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</sect1>
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<sect1 id="Transport_classes">
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<title>Transport classes</title>
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<para>
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Transport classes are service libraries for drivers in the SCSI
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lower layer, which expose transport attributes in sysfs.
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</para>
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<sect2 id="Fibre_Channel_transport">
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<title>Fibre Channel transport</title>
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<para>
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The file drivers/scsi/scsi_transport_fc.c defines transport attributes
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for Fibre Channel.
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</para>
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!Edrivers/scsi/scsi_transport_fc.c
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</sect2>
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<sect2 id="iSCSI_transport">
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<title>iSCSI transport class</title>
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<para>
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The file drivers/scsi/scsi_transport_iscsi.c defines transport
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attributes for the iSCSI class, which sends SCSI packets over TCP/IP
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connections.
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</para>
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!Edrivers/scsi/scsi_transport_iscsi.c
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</sect2>
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<sect2 id="SAS_transport">
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<title>Serial Attached SCSI (SAS) transport class</title>
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<para>
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The file drivers/scsi/scsi_transport_sas.c defines transport
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attributes for Serial Attached SCSI, a variant of SATA aimed at
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large high-end systems.
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</para>
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<para>
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The SAS transport class contains common code to deal with SAS HBAs,
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an aproximated representation of SAS topologies in the driver model,
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and various sysfs attributes to expose these topologies and management
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interfaces to userspace.
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</para>
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<para>
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In addition to the basic SCSI core objects this transport class
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introduces two additional intermediate objects: The SAS PHY
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as represented by struct sas_phy defines an "outgoing" PHY on
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a SAS HBA or Expander, and the SAS remote PHY represented by
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struct sas_rphy defines an "incoming" PHY on a SAS Expander or
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end device. Note that this is purely a software concept, the
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underlying hardware for a PHY and a remote PHY is the exactly
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the same.
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</para>
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<para>
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There is no concept of a SAS port in this code, users can see
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what PHYs form a wide port based on the port_identifier attribute,
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which is the same for all PHYs in a port.
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</para>
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!Edrivers/scsi/scsi_transport_sas.c
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</sect2>
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<sect2 id="SATA_transport">
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<title>SATA transport class</title>
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<para>
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The SATA transport is handled by libata, which has its own book of
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documentation in this directory.
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</para>
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</sect2>
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<sect2 id="SPI_transport">
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<title>Parallel SCSI (SPI) transport class</title>
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<para>
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The file drivers/scsi/scsi_transport_spi.c defines transport
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attributes for traditional (fast/wide/ultra) SCSI busses.
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</para>
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!Edrivers/scsi/scsi_transport_spi.c
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</sect2>
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<sect2 id="SRP_transport">
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<title>SCSI RDMA (SRP) transport class</title>
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<para>
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The file drivers/scsi/scsi_transport_srp.c defines transport
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attributes for SCSI over Remote Direct Memory Access.
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</para>
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!Edrivers/scsi/scsi_transport_srp.c
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</sect2>
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</sect1>
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</chapter>
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<chapter id="lower_layer">
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<title>SCSI lower layer</title>
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<sect1 id="hba_drivers">
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<title>Host Bus Adapter transport types</title>
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<para>
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Many modern device controllers use the SCSI command set as a protocol to
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communicate with their devices through many different types of physical
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connections.
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</para>
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<para>
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In SCSI language a bus capable of carrying SCSI commands is
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called a "transport", and a controller connecting to such a bus is
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called a "host bus adapter" (HBA).
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</para>
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<sect2 id="scsi_debug.c">
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<title>Debug transport</title>
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<para>
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The file drivers/scsi/scsi_debug.c simulates a host adapter with a
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variable number of disks (or disk like devices) attached, sharing a
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common amount of RAM. Does a lot of checking to make sure that we are
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not getting blocks mixed up, and panics the kernel if anything out of
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the ordinary is seen.
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</para>
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<para>
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To be more realistic, the simulated devices have the transport
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attributes of SAS disks.
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</para>
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<para>
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For documentation see
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<ulink url='http://sg.danny.cz/sg/sdebug26.html'>http://sg.danny.cz/sg/sdebug26.html</ulink>
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</para>
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<!-- !Edrivers/scsi/scsi_debug.c -->
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</sect2>
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<sect2 id="todo">
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<title>todo</title>
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<para>Parallel (fast/wide/ultra) SCSI, USB, SATA,
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SAS, Fibre Channel, FireWire, ATAPI devices, Infiniband,
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I20, iSCSI, Parallel ports, netlink...
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</para>
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</sect2>
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</sect1>
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</chapter>
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</book>
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