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Rob Landleyeb448202007-11-03 13:30:39 -05001<?xml version="1.0" encoding="UTF-8"?>
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4
5<book id="scsimid">
6 <bookinfo>
Randy Dunlapdc8875e2007-11-15 15:42:30 -08007 <title>SCSI Interfaces Guide</title>
Rob Landleyeb448202007-11-03 13:30:39 -05008
9 <authorgroup>
10 <author>
11 <firstname>James</firstname>
12 <surname>Bottomley</surname>
13 <affiliation>
14 <address>
James Bottomley99cb8132008-02-03 16:00:12 -060015 <email>James.Bottomley@hansenpartnership.com</email>
Rob Landleyeb448202007-11-03 13:30:39 -050016 </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
Randy Dunlapdc8875e2007-11-15 15:42:30 -080095 upper layer driver, one lower layer driver, and the SCSI midlayer.
Rob Landleyeb448202007-11-03 13:30:39 -050096 </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>
Randy Dunlapdc8875e2007-11-15 15:42:30 -0800157 <para>Main file for the SCSI midlayer.</para>
Rob Landleyeb448202007-11-03 13:30:39 -0500158!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>
Randy Dunlapdc8875e2007-11-15 15:42:30 -0800185 Handle ioctl() calls for SCSI devices.
Rob Landleyeb448202007-11-03 13:30:39 -0500186 </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>
Randy Dunlapdc8875e2007-11-15 15:42:30 -0800290 Transport classes are service libraries for drivers in the SCSI
Rob Landleyeb448202007-11-03 13:30:39 -0500291 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,
Uwe Kleine-Koenig3dbda772009-07-23 08:31:31 +0200320 and various sysfs attributes to expose these topologies and management
Rob Landleyeb448202007-11-03 13:30:39 -0500321 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://www.torque.net/sg/sdebug26.html'>http://www.torque.net/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>