[SCSI] remove Documentation/DocBook/scsidrivers.tmpl

DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml videobook.xml \

	    kernel-hacking.xml kernel-locking.xml via-audio.xml \

	    deviceiobook.xml procfs-guide.xml tulip-user.xml \

	    writing_usb_driver.xml scsidrivers.xml sis900.xml \

	    kernel-api.xml journal-api.xml lsm.xml usb.xml \

	    gadget.xml libata.xml mtdnand.xml librs.xml

	    writing_usb_driver.xml sis900.xml kernel-api.xml \

	    journal-api.xml lsm.xml usb.xml gadget.xml libata.xml \

	    mtdnand.xml librs.xml

###

# The build process is as follows (targets):

<?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>