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diff --git a/Documentation/DocBook/scsidrivers.tmpl b/Documentation/DocBook/scsidrivers.tmpl new file mode 100644 index 0000000..d058e65 --- /dev/null +++ b/Documentation/DocBook/scsidrivers.tmpl @@ -0,0 +1,193 @@ +<?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> |
