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Based on kernel version 3.13. Page generated on 2014-01-20 22:02 EST.

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>
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