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   1<?xml version="1.0" encoding="UTF-8"?>
   2<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
   3        "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
   4
   5<book id="scsimid">
   6  <bookinfo>
   7    <title>SCSI Interfaces Guide</title>
   8
   9    <authorgroup>
  10      <author>
  11        <firstname>James</firstname>
  12        <surname>Bottomley</surname>
  13        <affiliation>
  14          <address>
  15            <email>James.Bottomley@hansenpartnership.com</email>
  16          </address>
  17        </affiliation>
  18      </author>
  19
  20      <author>
  21        <firstname>Rob</firstname>
  22        <surname>Landley</surname>
  23        <affiliation>
  24          <address>
  25            <email>rob@landley.net</email>
  26          </address>
  27        </affiliation>
  28      </author>
  29
  30    </authorgroup>
  31
  32    <copyright>
  33      <year>2007</year>
  34      <holder>Linux Foundation</holder>
  35    </copyright>
  36
  37    <legalnotice>
  38      <para>
  39        This documentation is free software; you can redistribute
  40        it and/or modify it under the terms of the GNU General Public
  41        License version 2.
  42      </para>
  43
  44      <para>
  45        This program is distributed in the hope that it will be
  46        useful, but WITHOUT ANY WARRANTY; without even the implied
  47        warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  48        For more details see the file COPYING in the source
  49        distribution of Linux.
  50      </para>
  51    </legalnotice>
  52  </bookinfo>
  53
  54  <toc></toc>
  55
  56  <chapter id="intro">
  57    <title>Introduction</title>
  58    <sect1 id="protocol_vs_bus">
  59      <title>Protocol vs bus</title>
  60      <para>
  61        Once upon a time, the Small Computer Systems Interface defined both
  62        a parallel I/O bus and a data protocol to connect a wide variety of
  63        peripherals (disk drives, tape drives, modems, printers, scanners,
  64        optical drives, test equipment, and medical devices) to a host
  65        computer.
  66      </para>
  67      <para>
  68        Although the old parallel (fast/wide/ultra) SCSI bus has largely
  69        fallen out of use, the SCSI command set is more widely used than ever
  70        to communicate with devices over a number of different busses.
  71      </para>
  72      <para>
  73        The <ulink url='http://www.t10.org/scsi-3.htm'>SCSI protocol</ulink>
  74        is a big-endian peer-to-peer packet based protocol.  SCSI commands
  75        are 6, 10, 12, or 16 bytes long, often followed by an associated data
  76        payload.
  77      </para>
  78      <para>
  79        SCSI commands can be transported over just about any kind of bus, and
  80        are the default protocol for storage devices attached to USB, SATA,
  81        SAS, Fibre Channel, FireWire, and ATAPI devices.  SCSI packets are
  82        also commonly exchanged over Infiniband,
  83        <ulink url='http://i2o.shadowconnect.com/faq.php'>I20</ulink>, TCP/IP
  84        (<ulink url='http://en.wikipedia.org/wiki/ISCSI'>iSCSI</ulink>), even
  85        <ulink url='http://cyberelk.net/tim/parport/parscsi.html'>Parallel
  86        ports</ulink>.
  87      </para>
  88    </sect1>
  89    <sect1 id="subsystem_design">
  90      <title>Design of the Linux SCSI subsystem</title>
  91      <para>
  92        The SCSI subsystem uses a three layer design, with upper, mid, and low
  93        layers.  Every operation involving the SCSI subsystem (such as reading
  94        a sector from a disk) uses one driver at each of the 3 levels: one
  95        upper layer driver, one lower layer driver, and the SCSI midlayer.
  96      </para>
  97      <para>
  98        The SCSI upper layer provides the interface between userspace and the
  99        kernel, in the form of block and char device nodes for I/O and
 100        ioctl().  The SCSI lower layer contains drivers for specific hardware
 101        devices.
 102      </para>
 103      <para>
 104        In between is the SCSI mid-layer, analogous to a network routing
 105        layer such as the IPv4 stack.  The SCSI mid-layer routes a packet
 106        based data protocol between the upper layer's /dev nodes and the
 107        corresponding devices in the lower layer.  It manages command queues,
 108        provides error handling and power management functions, and responds
 109        to ioctl() requests.
 110      </para>
 111    </sect1>
 112  </chapter>
 113
 114  <chapter id="upper_layer">
 115    <title>SCSI upper layer</title>
 116    <para>
 117      The upper layer supports the user-kernel interface by providing
 118      device nodes.
 119    </para>
 120    <sect1 id="sd">
 121      <title>sd (SCSI Disk)</title>
 122      <para>sd (sd_mod.o)</para>
 123<!-- !Idrivers/scsi/sd.c -->
 124    </sect1>
 125    <sect1 id="sr">
 126      <title>sr (SCSI CD-ROM)</title>
 127      <para>sr (sr_mod.o)</para>
 128    </sect1>
 129    <sect1 id="st">
 130      <title>st (SCSI Tape)</title>
 131      <para>st (st.o)</para>
 132    </sect1>
 133    <sect1 id="sg">
 134      <title>sg (SCSI Generic)</title>
 135      <para>sg (sg.o)</para>
 136    </sect1>
 137    <sect1 id="ch">
 138      <title>ch (SCSI Media Changer)</title>
 139      <para>ch (ch.c)</para>
 140    </sect1>
 141  </chapter>
 142
 143  <chapter id="mid_layer">
 144    <title>SCSI mid layer</title>
 145
 146    <sect1 id="midlayer_implementation">
 147      <title>SCSI midlayer implementation</title>
 148      <sect2 id="scsi_device.h">
 149        <title>include/scsi/scsi_device.h</title>
 150        <para>
 151        </para>
 152!Iinclude/scsi/scsi_device.h
 153      </sect2>
 154
 155      <sect2 id="scsi.c">
 156        <title>drivers/scsi/scsi.c</title>
 157        <para>Main file for the SCSI midlayer.</para>
 158!Edrivers/scsi/scsi.c
 159      </sect2>
 160      <sect2 id="scsicam.c">
 161        <title>drivers/scsi/scsicam.c</title>
 162        <para>
 163          <ulink url='http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf'>SCSI
 164          Common Access Method</ulink> support functions, for use with
 165          HDIO_GETGEO, etc.
 166        </para>
 167!Edrivers/scsi/scsicam.c
 168      </sect2>
 169      <sect2 id="scsi_error.c">
 170        <title>drivers/scsi/scsi_error.c</title>
 171        <para>Common SCSI error/timeout handling routines.</para>
 172!Edrivers/scsi/scsi_error.c
 173      </sect2>
 174      <sect2 id="scsi_devinfo.c">
 175        <title>drivers/scsi/scsi_devinfo.c</title>
 176        <para>
 177          Manage scsi_dev_info_list, which tracks blacklisted and whitelisted
 178          devices.
 179        </para>
 180!Idrivers/scsi/scsi_devinfo.c
 181      </sect2>
 182      <sect2 id="scsi_ioctl.c">
 183        <title>drivers/scsi/scsi_ioctl.c</title>
 184        <para>
 185          Handle ioctl() calls for SCSI devices.
 186        </para>
 187!Edrivers/scsi/scsi_ioctl.c
 188      </sect2>
 189      <sect2 id="scsi_lib.c">
 190        <title>drivers/scsi/scsi_lib.c</title>
 191        <para>
 192          SCSI queuing library.
 193        </para>
 194!Edrivers/scsi/scsi_lib.c
 195      </sect2>
 196      <sect2 id="scsi_lib_dma.c">
 197        <title>drivers/scsi/scsi_lib_dma.c</title>
 198        <para>
 199          SCSI library functions depending on DMA
 200          (map and unmap scatter-gather lists).
 201        </para>
 202!Edrivers/scsi/scsi_lib_dma.c
 203      </sect2>
 204      <sect2 id="scsi_module.c">
 205        <title>drivers/scsi/scsi_module.c</title>
 206        <para>
 207          The file drivers/scsi/scsi_module.c contains legacy support for
 208          old-style host templates.  It should never be used by any new driver.
 209        </para>
 210      </sect2>
 211      <sect2 id="scsi_proc.c">
 212        <title>drivers/scsi/scsi_proc.c</title>
 213        <para>
 214          The functions in this file provide an interface between
 215          the PROC file system and the SCSI device drivers
 216          It is mainly used for debugging, statistics and to pass
 217          information directly to the lowlevel driver.
 218
 219          I.E. plumbing to manage /proc/scsi/*
 220        </para>
 221!Idrivers/scsi/scsi_proc.c
 222      </sect2>
 223      <sect2 id="scsi_netlink.c">
 224        <title>drivers/scsi/scsi_netlink.c</title>
 225        <para>
 226          Infrastructure to provide async events from transports to userspace
 227          via netlink, using a single NETLINK_SCSITRANSPORT protocol for all
 228          transports.
 229
 230          See <ulink url='http://marc.info/?l=linux-scsi&amp;m=115507374832500&amp;w=2'>the
 231          original patch submission</ulink> for more details.
 232        </para>
 233!Idrivers/scsi/scsi_netlink.c
 234      </sect2>
 235      <sect2 id="scsi_scan.c">
 236        <title>drivers/scsi/scsi_scan.c</title>
 237        <para>
 238          Scan a host to determine which (if any) devices are attached.
 239
 240          The general scanning/probing algorithm is as follows, exceptions are
 241          made to it depending on device specific flags, compilation options,
 242          and global variable (boot or module load time) settings.
 243
 244          A specific LUN is scanned via an INQUIRY command; if the LUN has a
 245          device attached, a scsi_device is allocated and setup for it.
 246
 247          For every id of every channel on the given host, start by scanning
 248          LUN 0.  Skip hosts that don't respond at all to a scan of LUN 0.
 249          Otherwise, if LUN 0 has a device attached, allocate and setup a
 250          scsi_device for it.  If target is SCSI-3 or up, issue a REPORT LUN,
 251          and scan all of the LUNs returned by the REPORT LUN; else,
 252          sequentially scan LUNs up until some maximum is reached, or a LUN is
 253          seen that cannot have a device attached to it.
 254        </para>
 255!Idrivers/scsi/scsi_scan.c
 256      </sect2>
 257      <sect2 id="scsi_sysctl.c">
 258        <title>drivers/scsi/scsi_sysctl.c</title>
 259        <para>
 260          Set up the sysctl entry: "/dev/scsi/logging_level"
 261          (DEV_SCSI_LOGGING_LEVEL) which sets/returns scsi_logging_level.
 262        </para>
 263      </sect2>
 264      <sect2 id="scsi_sysfs.c">
 265        <title>drivers/scsi/scsi_sysfs.c</title>
 266        <para>
 267          SCSI sysfs interface routines.
 268        </para>
 269!Edrivers/scsi/scsi_sysfs.c
 270      </sect2>
 271      <sect2 id="hosts.c">
 272        <title>drivers/scsi/hosts.c</title>
 273        <para>
 274          mid to lowlevel SCSI driver interface
 275        </para>
 276!Edrivers/scsi/hosts.c
 277      </sect2>
 278      <sect2 id="constants.c">
 279        <title>drivers/scsi/constants.c</title>
 280        <para>
 281          mid to lowlevel SCSI driver interface
 282        </para>
 283!Edrivers/scsi/constants.c
 284      </sect2>
 285    </sect1>
 286
 287    <sect1 id="Transport_classes">
 288      <title>Transport classes</title>
 289      <para>
 290        Transport classes are service libraries for drivers in the SCSI
 291        lower layer, which expose transport attributes in sysfs.
 292      </para>
 293      <sect2 id="Fibre_Channel_transport">
 294        <title>Fibre Channel transport</title>
 295        <para>
 296          The file drivers/scsi/scsi_transport_fc.c defines transport attributes
 297          for Fibre Channel.
 298        </para>
 299!Edrivers/scsi/scsi_transport_fc.c
 300      </sect2>
 301      <sect2 id="iSCSI_transport">
 302        <title>iSCSI transport class</title>
 303        <para>
 304          The file drivers/scsi/scsi_transport_iscsi.c defines transport
 305          attributes for the iSCSI class, which sends SCSI packets over TCP/IP
 306          connections.
 307        </para>
 308!Edrivers/scsi/scsi_transport_iscsi.c
 309      </sect2>
 310      <sect2 id="SAS_transport">
 311        <title>Serial Attached SCSI (SAS) transport class</title>
 312        <para>
 313          The file drivers/scsi/scsi_transport_sas.c defines transport
 314          attributes for Serial Attached SCSI, a variant of SATA aimed at
 315          large high-end systems.
 316        </para>
 317        <para>
 318          The SAS transport class contains common code to deal with SAS HBAs,
 319          an aproximated representation of SAS topologies in the driver model,
 320          and various sysfs attributes to expose these topologies and management
 321          interfaces to userspace.
 322        </para>
 323        <para>
 324          In addition to the basic SCSI core objects this transport class
 325          introduces two additional intermediate objects:  The SAS PHY
 326          as represented by struct sas_phy defines an "outgoing" PHY on
 327          a SAS HBA or Expander, and the SAS remote PHY represented by
 328          struct sas_rphy defines an "incoming" PHY on a SAS Expander or
 329          end device.  Note that this is purely a software concept, the
 330          underlying hardware for a PHY and a remote PHY is the exactly
 331          the same.
 332        </para>
 333        <para>
 334          There is no concept of a SAS port in this code, users can see
 335          what PHYs form a wide port based on the port_identifier attribute,
 336          which is the same for all PHYs in a port.
 337        </para>
 338!Edrivers/scsi/scsi_transport_sas.c
 339      </sect2>
 340      <sect2 id="SATA_transport">
 341        <title>SATA transport class</title>
 342        <para>
 343          The SATA transport is handled by libata, which has its own book of
 344          documentation in this directory.
 345        </para>
 346      </sect2>
 347      <sect2 id="SPI_transport">
 348        <title>Parallel SCSI (SPI) transport class</title>
 349        <para>
 350          The file drivers/scsi/scsi_transport_spi.c defines transport
 351          attributes for traditional (fast/wide/ultra) SCSI busses.
 352        </para>
 353!Edrivers/scsi/scsi_transport_spi.c
 354      </sect2>
 355      <sect2 id="SRP_transport">
 356        <title>SCSI RDMA (SRP) transport class</title>
 357        <para>
 358          The file drivers/scsi/scsi_transport_srp.c defines transport
 359          attributes for SCSI over Remote Direct Memory Access.
 360        </para>
 361!Edrivers/scsi/scsi_transport_srp.c
 362      </sect2>
 363    </sect1>
 364
 365  </chapter>
 366
 367  <chapter id="lower_layer">
 368    <title>SCSI lower layer</title>
 369    <sect1 id="hba_drivers">
 370      <title>Host Bus Adapter transport types</title>
 371      <para>
 372        Many modern device controllers use the SCSI command set as a protocol to
 373        communicate with their devices through many different types of physical
 374        connections.
 375      </para>
 376      <para>
 377        In SCSI language a bus capable of carrying SCSI commands is
 378        called a "transport", and a controller connecting to such a bus is
 379        called a "host bus adapter" (HBA).
 380      </para>
 381      <sect2 id="scsi_debug.c">
 382        <title>Debug transport</title>
 383        <para>
 384          The file drivers/scsi/scsi_debug.c simulates a host adapter with a
 385          variable number of disks (or disk like devices) attached, sharing a
 386          common amount of RAM.  Does a lot of checking to make sure that we are
 387          not getting blocks mixed up, and panics the kernel if anything out of
 388          the ordinary is seen.
 389        </para>
 390        <para>
 391          To be more realistic, the simulated devices have the transport
 392          attributes of SAS disks.
 393        </para>
 394        <para>
 395          For documentation see
 396          <ulink url='http://sg.danny.cz/sg/sdebug26.html'>http://sg.danny.cz/sg/sdebug26.html</ulink>
 397        </para>
 398<!-- !Edrivers/scsi/scsi_debug.c -->
 399      </sect2>
 400      <sect2 id="todo">
 401        <title>todo</title>
 402        <para>Parallel (fast/wide/ultra) SCSI, USB, SATA,
 403        SAS, Fibre Channel, FireWire, ATAPI devices, Infiniband,
 404        I20, iSCSI, Parallel ports, netlink...
 405        </para>
 406      </sect2>
 407    </sect1>
 408  </chapter>
 409</book>
 410
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