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&m=115507374832500&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