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| <?xml version="1.0" encoding="UTF-8"?> | ||
| <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" | ||
| "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> | ||
|
|
||
| <book id="scsidrivers"> | ||
| <bookinfo> | ||
| <title>SCSI Subsystem Interfaces</title> | ||
|
|
||
| <authorgroup> | ||
| <author> | ||
| <firstname>Douglas</firstname> | ||
| <surname>Gilbert</surname> | ||
| <affiliation> | ||
| <address> | ||
| <email>dgilbert@interlog.com</email> | ||
| </address> | ||
| </affiliation> | ||
| </author> | ||
| </authorgroup> | ||
| <pubdate>2003-08-11</pubdate> | ||
|
|
||
| <copyright> | ||
| <year>2002</year> | ||
| <year>2003</year> | ||
| <holder>Douglas Gilbert</holder> | ||
| </copyright> | ||
|
|
||
| <legalnotice> | ||
| <para> | ||
| This documentation is free software; you can redistribute | ||
| it and/or modify it under the terms of the GNU General Public | ||
| License as published by the Free Software Foundation; either | ||
| version 2 of the License, or (at your option) any later | ||
| version. | ||
| </para> | ||
|
|
||
| <para> | ||
| This program is distributed in the hope that it will be | ||
| useful, but WITHOUT ANY WARRANTY; without even the implied | ||
| warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. | ||
| See the GNU General Public License for more details. | ||
| </para> | ||
|
|
||
| <para> | ||
| You should have received a copy of the GNU General Public | ||
| License along with this program; if not, write to the Free | ||
| Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, | ||
| MA 02111-1307 USA | ||
| </para> | ||
|
|
||
| <para> | ||
| For more details see the file COPYING in the source | ||
| distribution of Linux. | ||
| </para> | ||
| </legalnotice> | ||
|
|
||
| </bookinfo> | ||
|
|
||
| <toc></toc> | ||
|
|
||
| <chapter id="intro"> | ||
| <title>Introduction</title> | ||
| <para> | ||
| This document outlines the interface between the Linux scsi mid level | ||
| and lower level drivers. Lower level drivers are variously called HBA | ||
| (host bus adapter) drivers, host drivers (HD) or pseudo adapter drivers. | ||
| The latter alludes to the fact that a lower level driver may be a | ||
| bridge to another IO subsystem (and the "ide-scsi" driver is an example | ||
| of this). There can be many lower level drivers active in a running | ||
| system, but only one per hardware type. For example, the aic7xxx driver | ||
| controls adaptec controllers based on the 7xxx chip series. Most lower | ||
| level drivers can control one or more scsi hosts (a.k.a. scsi initiators). | ||
| </para> | ||
| <para> | ||
| This document can been found in an ASCII text file in the linux kernel | ||
| source: <filename>Documentation/scsi/scsi_mid_low_api.txt</filename> . | ||
| It currently hold a little more information than this document. The | ||
| <filename>drivers/scsi/hosts.h</filename> and <filename> | ||
| drivers/scsi/scsi.h</filename> headers contain descriptions of members | ||
| of important structures for the scsi subsystem. | ||
| </para> | ||
| </chapter> | ||
|
|
||
| <chapter id="driver-struct"> | ||
| <title>Driver structure</title> | ||
| <para> | ||
| Traditionally a lower level driver for the scsi subsystem has been | ||
| at least two files in the drivers/scsi directory. For example, a | ||
| driver called "xyz" has a header file "xyz.h" and a source file | ||
| "xyz.c". [Actually there is no good reason why this couldn't all | ||
| be in one file.] Some drivers that have been ported to several operating | ||
| systems (e.g. aic7xxx which has separate files for generic and | ||
| OS-specific code) have more than two files. Such drivers tend to have | ||
| their own directory under the drivers/scsi directory. | ||
| </para> | ||
| <para> | ||
| scsi_module.c is normally included at the end of a lower | ||
| level driver. For it to work a declaration like this is needed before | ||
| it is included: | ||
| <programlisting> | ||
| static Scsi_Host_Template driver_template = DRIVER_TEMPLATE; | ||
| /* DRIVER_TEMPLATE should contain pointers to supported interface | ||
| functions. Scsi_Host_Template is defined hosts.h */ | ||
| #include "scsi_module.c" | ||
| </programlisting> | ||
| </para> | ||
| <para> | ||
| The scsi_module.c assumes the name "driver_template" is appropriately | ||
| defined. It contains 2 functions: | ||
| <orderedlist> | ||
| <listitem><para> | ||
| init_this_scsi_driver() called during builtin and module driver | ||
| initialization: invokes mid level's scsi_register_host() | ||
| </para></listitem> | ||
| <listitem><para> | ||
| exit_this_scsi_driver() called during closedown: invokes | ||
| mid level's scsi_unregister_host() | ||
| </para></listitem> | ||
| </orderedlist> | ||
| </para> | ||
| <para> | ||
| When a new, lower level driver is being added to Linux, the following | ||
| files (all found in the drivers/scsi directory) will need some attention: | ||
| Makefile, Config.help and Config.in . It is probably best to look at what | ||
| an existing lower level driver does in this regard. | ||
| </para> | ||
| </chapter> | ||
|
|
||
| <chapter id="intfunctions"> | ||
| <title>Interface Functions</title> | ||
| !EDocumentation/scsi/scsi_mid_low_api.txt | ||
| </chapter> | ||
|
|
||
| <chapter id="locks"> | ||
| <title>Locks</title> | ||
| <para> | ||
| Each Scsi_Host instance has a spin_lock called Scsi_Host::default_lock | ||
| which is initialized in scsi_register() [found in hosts.c]. Within the | ||
| same function the Scsi_Host::host_lock pointer is initialized to point | ||
| at default_lock with the scsi_assign_lock() function. Thereafter | ||
| lock and unlock operations performed by the mid level use the | ||
| Scsi_Host::host_lock pointer. | ||
| </para> | ||
| <para> | ||
| Lower level drivers can override the use of Scsi_Host::default_lock by | ||
| using scsi_assign_lock(). The earliest opportunity to do this would | ||
| be in the detect() function after it has invoked scsi_register(). It | ||
| could be replaced by a coarser grain lock (e.g. per driver) or a | ||
| lock of equal granularity (i.e. per host). Using finer grain locks | ||
| (e.g. per scsi device) may be possible by juggling locks in | ||
| queuecommand(). | ||
| </para> | ||
| </chapter> | ||
|
|
||
| <chapter id="changes"> | ||
| <title>Changes since lk 2.4 series</title> | ||
| <para> | ||
| io_request_lock has been replaced by several finer grained locks. The lock | ||
| relevant to lower level drivers is Scsi_Host::host_lock and there is one | ||
| per scsi host. | ||
| </para> | ||
| <para> | ||
| The older error handling mechanism has been removed. This means the | ||
| lower level interface functions abort() and reset() have been removed. | ||
| </para> | ||
| <para> | ||
| In the 2.4 series the scsi subsystem configuration descriptions were | ||
| aggregated with the configuration descriptions from all other Linux | ||
| subsystems in the Documentation/Configure.help file. In the 2.5 series, | ||
| the scsi subsystem now has its own (much smaller) drivers/scsi/Config.help | ||
| file. | ||
| </para> | ||
| </chapter> | ||
|
|
||
| <chapter id="credits"> | ||
| <title>Credits</title> | ||
| <para> | ||
| The following people have contributed to this document: | ||
| <orderedlist> | ||
| <listitem><para> | ||
| Mike Anderson <email>andmike@us.ibm.com</email> | ||
| </para></listitem> | ||
| <listitem><para> | ||
| James Bottomley <email>James.Bottomley@steeleye.com</email> | ||
| </para></listitem> | ||
| <listitem><para> | ||
| Patrick Mansfield <email>patmans@us.ibm.com</email> | ||
| </para></listitem> | ||
| </orderedlist> | ||
| </para> | ||
| </chapter> | ||
|
|
||
| </book> |
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