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