Commit eb44820c authored by Rob Landley's avatar Rob Landley Committed by James Bottomley
Browse files

[SCSI] Add Documentation and integrate into docbook build 



Add Documentation/DocBook/scsi_midlayer.tmpl, add to Makefile, and update
lots of kerneldoc comments in drivers/scsi/*.

Updated with comments from Stefan Richter, Stephen M. Cameron,
 James Bottomley and Randy Dunlap.

Signed-off-by: default avatarRob Landley <rob@landley.net>
Signed-off-by: default avatarJames Bottomley <James.Bottomley@HansenPartnership.com>
parent 3f489858

Documentation/DocBook/Makefile

+1 −1
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@@ -11,7 +11,7 @@ DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml videobook.xml \ 
	    procfs-guide.xml writing_usb_driver.xml \

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

	    gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \

	    genericirq.xml s390-drivers.xml uio-howto.xml

	    genericirq.xml s390-drivers.xml uio-howto.xml scsi_midlayer.xml



###

# The build process is as follows (targets):

Documentation/DocBook/scsi_midlayer.tmpl

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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="scsimid">

  <bookinfo>

    <title>SCSI Mid Layer Guide</title>



    <authorgroup>

      <author>

        <firstname>James</firstname>

        <surname>Bottomley</surname>

        <affiliation>

          <address>

            <email>James.Bottomley@steeleye.com</email>

          </address>

        </affiliation>

      </author>



      <author>

        <firstname>Rob</firstname>

        <surname>Landley</surname>

        <affiliation>

          <address>

            <email>rob@landley.net</email>

          </address>

        </affiliation>

      </author>



    </authorgroup>



    <copyright>

      <year>2007</year>

      <holder>Linux Foundation</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 version 2.

      </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.

        For more details see the file COPYING in the source

        distribution of Linux.

      </para>

    </legalnotice>

  </bookinfo>



  <toc></toc>



  <chapter id="intro">

    <title>Introduction</title>

    <sect1 id="protocol_vs_bus">

      <title>Protocol vs bus</title>

      <para>

        Once upon a time, the Small Computer Systems Interface defined both

        a parallel I/O bus and a data protocol to connect a wide variety of

        peripherals (disk drives, tape drives, modems, printers, scanners,

        optical drives, test equipment, and medical devices) to a host

        computer.

      </para>

      <para>

        Although the old parallel (fast/wide/ultra) SCSI bus has largely

        fallen out of use, the SCSI command set is more widely used than ever

        to communicate with devices over a number of different busses.

      </para>

      <para>

        The <ulink url='http://www.t10.org/scsi-3.htm'>SCSI protocol</ulink>

        is a big-endian peer-to-peer packet based protocol.  SCSI commands

        are 6, 10, 12, or 16 bytes long, often followed by an associated data

        payload.

      </para>

      <para>

        SCSI commands can be transported over just about any kind of bus, and

        are the default protocol for storage devices attached to USB, SATA,

        SAS, Fibre Channel, FireWire, and ATAPI devices.  SCSI packets are

        also commonly exchanged over Infiniband,

        <ulink url='http://i2o.shadowconnect.com/faq.php'>I20</ulink>, TCP/IP

        (<ulink url='http://en.wikipedia.org/wiki/ISCSI'>iSCSI</ulink>), even

        <ulink url='http://cyberelk.net/tim/parport/parscsi.html'>Parallel

        ports</ulink>.

      </para>

    </sect1>

    <sect1 id="subsystem_design">

      <title>Design of the Linux SCSI subsystem</title>

      <para>

        The SCSI subsystem uses a three layer design, with upper, mid, and low

        layers.  Every operation involving the SCSI subsystem (such as reading

        a sector from a disk) uses one driver at each of the 3 levels: one

        upper layer driver, one lower layer driver, and the scsi midlayer.

      </para>

      <para>

        The SCSI upper layer provides the interface between userspace and the

        kernel, in the form of block and char device nodes for I/O and

        ioctl().  The SCSI lower layer contains drivers for specific hardware

        devices.

      </para>

      <para>

        In between is the SCSI mid-layer, analogous to a network routing

        layer such as the IPv4 stack.  The SCSI mid-layer routes a packet

        based data protocol between the upper layer's /dev nodes and the

        corresponding devices in the lower layer.  It manages command queues,

        provides error handling and power management functions, and responds

        to ioctl() requests.

      </para>

    </sect1>

  </chapter>



  <chapter id="upper_layer">

    <title>SCSI upper layer</title>

    <para>

      The upper layer supports the user-kernel interface by providing

      device nodes.

    </para>

    <sect1 id="sd">

      <title>sd (SCSI Disk)</title>

      <para>sd (sd_mod.o)</para>

<!-- !Idrivers/scsi/sd.c -->

    </sect1>

    <sect1 id="sr">

      <title>sr (SCSI CD-ROM)</title>

      <para>sr (sr_mod.o)</para>

    </sect1>

    <sect1 id="st">

      <title>st (SCSI Tape)</title>

      <para>st (st.o)</para>

    </sect1>

    <sect1 id="sg">

      <title>sg (SCSI Generic)</title>

      <para>sg (sg.o)</para>

    </sect1>

    <sect1 id="ch">

      <title>ch (SCSI Media Changer)</title>

      <para>ch (ch.c)</para>

    </sect1>

  </chapter>



  <chapter id="mid_layer">

    <title>SCSI mid layer</title>



    <sect1 id="midlayer_implementation">

      <title>SCSI midlayer implementation</title>

      <sect2 id="scsi_device.h">

        <title>include/scsi/scsi_device.h</title>

        <para>

        </para>

!Iinclude/scsi/scsi_device.h

      </sect2>



      <sect2 id="scsi.c">

        <title>drivers/scsi/scsi.c</title>

        <para>Main file for the scsi midlayer.</para>

!Edrivers/scsi/scsi.c

      </sect2>

      <sect2 id="scsicam.c">

        <title>drivers/scsi/scsicam.c</title>

        <para>

          <ulink url='http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf'>SCSI

          Common Access Method</ulink> support functions, for use with

          HDIO_GETGEO, etc.

        </para>

!Edrivers/scsi/scsicam.c

      </sect2>

      <sect2 id="scsi_error.c">

        <title>drivers/scsi/scsi_error.c</title>

        <para>Common SCSI error/timeout handling routines.</para>

!Edrivers/scsi/scsi_error.c

      </sect2>

      <sect2 id="scsi_devinfo.c">

        <title>drivers/scsi/scsi_devinfo.c</title>

        <para>

          Manage scsi_dev_info_list, which tracks blacklisted and whitelisted

          devices.

        </para>

!Idrivers/scsi/scsi_devinfo.c

      </sect2>

      <sect2 id="scsi_ioctl.c">

        <title>drivers/scsi/scsi_ioctl.c</title>

        <para>

          Handle ioctl() calls for scsi devices.

        </para>

!Edrivers/scsi/scsi_ioctl.c

      </sect2>

      <sect2 id="scsi_lib.c">

        <title>drivers/scsi/scsi_lib.c</title>

        <para>

          SCSI queuing library.

        </para>

!Edrivers/scsi/scsi_lib.c

      </sect2>

      <sect2 id="scsi_lib_dma.c">

        <title>drivers/scsi/scsi_lib_dma.c</title>

        <para>

          SCSI library functions depending on DMA

          (map and unmap scatter-gather lists).

        </para>

!Edrivers/scsi/scsi_lib_dma.c

      </sect2>

      <sect2 id="scsi_module.c">

        <title>drivers/scsi/scsi_module.c</title>

        <para>

          The file drivers/scsi/scsi_module.c contains legacy support for

          old-style host templates.  It should never be used by any new driver.

        </para>

      </sect2>

      <sect2 id="scsi_proc.c">

        <title>drivers/scsi/scsi_proc.c</title>

        <para>

          The functions in this file provide an interface between

          the PROC file system and the SCSI device drivers

          It is mainly used for debugging, statistics and to pass

          information directly to the lowlevel driver.



          I.E. plumbing to manage /proc/scsi/*

        </para>

!Idrivers/scsi/scsi_proc.c

      </sect2>

      <sect2 id="scsi_netlink.c">

        <title>drivers/scsi/scsi_netlink.c</title>

        <para>

          Infrastructure to provide async events from transports to userspace

          via netlink, using a single NETLINK_SCSITRANSPORT protocol for all

          transports.



          See <ulink url='http://marc.info/?l=linux-scsi&amp;m=115507374832500&amp;w=2'>the

          original patch submission</ulink> for more details.

        </para>

!Idrivers/scsi/scsi_netlink.c

      </sect2>

      <sect2 id="scsi_scan.c">

        <title>drivers/scsi/scsi_scan.c</title>

        <para>

          Scan a host to determine which (if any) devices are attached.



          The general scanning/probing algorithm is as follows, exceptions are

          made to it depending on device specific flags, compilation options,

          and global variable (boot or module load time) settings.



          A specific LUN is scanned via an INQUIRY command; if the LUN has a

          device attached, a scsi_device is allocated and setup for it.



          For every id of every channel on the given host, start by scanning

          LUN 0.  Skip hosts that don't respond at all to a scan of LUN 0.

          Otherwise, if LUN 0 has a device attached, allocate and setup a

          scsi_device for it.  If target is SCSI-3 or up, issue a REPORT LUN,

          and scan all of the LUNs returned by the REPORT LUN; else,

          sequentially scan LUNs up until some maximum is reached, or a LUN is

          seen that cannot have a device attached to it.

        </para>

!Idrivers/scsi/scsi_scan.c

      </sect2>

      <sect2 id="scsi_sysctl.c">

        <title>drivers/scsi/scsi_sysctl.c</title>

        <para>

          Set up the sysctl entry: "/dev/scsi/logging_level"

          (DEV_SCSI_LOGGING_LEVEL) which sets/returns scsi_logging_level.

        </para>

      </sect2>

      <sect2 id="scsi_sysfs.c">

        <title>drivers/scsi/scsi_sysfs.c</title>

        <para>

          SCSI sysfs interface routines.

        </para>

!Edrivers/scsi/scsi_sysfs.c

      </sect2>

      <sect2 id="hosts.c">

        <title>drivers/scsi/hosts.c</title>

        <para>

          mid to lowlevel SCSI driver interface

        </para>

!Edrivers/scsi/hosts.c

      </sect2>

      <sect2 id="constants.c">

        <title>drivers/scsi/constants.c</title>

        <para>

          mid to lowlevel SCSI driver interface

        </para>

!Edrivers/scsi/constants.c

      </sect2>

    </sect1>



    <sect1 id="Transport_classes">

      <title>Transport classes</title>

      <para>

        Transport classes are service libraries for drivers in the scsi

        lower layer, which expose transport attributes in sysfs.

      </para>

      <sect2 id="Fibre_Channel_transport">

        <title>Fibre Channel transport</title>

        <para>

          The file drivers/scsi/scsi_transport_fc.c defines transport attributes

          for Fibre Channel.

        </para>

!Edrivers/scsi/scsi_transport_fc.c

      </sect2>

      <sect2 id="iSCSI_transport">

        <title>iSCSI transport class</title>

        <para>

          The file drivers/scsi/scsi_transport_iscsi.c defines transport

          attributes for the iSCSI class, which sends SCSI packets over TCP/IP

          connections.

        </para>

!Edrivers/scsi/scsi_transport_iscsi.c

      </sect2>

      <sect2 id="SAS_transport">

        <title>Serial Attached SCSI (SAS) transport class</title>

        <para>

          The file drivers/scsi/scsi_transport_sas.c defines transport

          attributes for Serial Attached SCSI, a variant of SATA aimed at

          large high-end systems.

        </para>

        <para>

          The SAS transport class contains common code to deal with SAS HBAs,

          an aproximated representation of SAS topologies in the driver model,

          and various sysfs attributes to expose these topologies and managment

          interfaces to userspace.

        </para>

        <para>

          In addition to the basic SCSI core objects this transport class

          introduces two additional intermediate objects:  The SAS PHY

          as represented by struct sas_phy defines an "outgoing" PHY on

          a SAS HBA or Expander, and the SAS remote PHY represented by

          struct sas_rphy defines an "incoming" PHY on a SAS Expander or

          end device.  Note that this is purely a software concept, the

          underlying hardware for a PHY and a remote PHY is the exactly

          the same.

        </para>

        <para>

          There is no concept of a SAS port in this code, users can see

          what PHYs form a wide port based on the port_identifier attribute,

          which is the same for all PHYs in a port.

        </para>

!Edrivers/scsi/scsi_transport_sas.c

      </sect2>

      <sect2 id="SATA_transport">

        <title>SATA transport class</title>

        <para>

          The SATA transport is handled by libata, which has its own book of

          documentation in this directory.

        </para>

      </sect2>

      <sect2 id="SPI_transport">

        <title>Parallel SCSI (SPI) transport class</title>

        <para>

          The file drivers/scsi/scsi_transport_spi.c defines transport

          attributes for traditional (fast/wide/ultra) SCSI busses.

        </para>

!Edrivers/scsi/scsi_transport_spi.c

      </sect2>

      <sect2 id="SRP_transport">

        <title>SCSI RDMA (SRP) transport class</title>

        <para>

          The file drivers/scsi/scsi_transport_srp.c defines transport

          attributes for SCSI over Remote Direct Memory Access.

        </para>

!Edrivers/scsi/scsi_transport_srp.c

      </sect2>

    </sect1>



  </chapter>



  <chapter id="lower_layer">

    <title>SCSI lower layer</title>

    <sect1 id="hba_drivers">

      <title>Host Bus Adapter transport types</title>

      <para>

        Many modern device controllers use the SCSI command set as a protocol to

        communicate with their devices through many different types of physical

        connections.

      </para>

      <para>

        In SCSI language a bus capable of carrying SCSI commands is

        called a "transport", and a controller connecting to such a bus is

        called a "host bus adapter" (HBA).

      </para>

      <sect2 id="scsi_debug.c">

        <title>Debug transport</title>

        <para>

          The file drivers/scsi/scsi_debug.c simulates a host adapter with a

          variable number of disks (or disk like devices) attached, sharing a

          common amount of RAM.  Does a lot of checking to make sure that we are

          not getting blocks mixed up, and panics the kernel if anything out of

          the ordinary is seen.

        </para>

        <para>

          To be more realistic, the simulated devices have the transport

          attributes of SAS disks.

        </para>

        <para>

          For documentation see

          <ulink url='http://www.torque.net/sg/sdebug26.html'>http://www.torque.net/sg/sdebug26.html</ulink>

        </para>

<!-- !Edrivers/scsi/scsi_debug.c -->

      </sect2>

      <sect2 id="todo">

        <title>todo</title>

        <para>Parallel (fast/wide/ultra) SCSI, USB, SATA,

        SAS, Fibre Channel, FireWire, ATAPI devices, Infiniband,

        I20, iSCSI, Parallel ports, netlink...

        </para>

      </sect2>

    </sect1>

  </chapter>

</book>

drivers/scsi/constants.c

+0 −1
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@@ -362,7 +362,6 @@ void scsi_print_command(struct scsi_cmnd *cmd) 
EXPORT_SYMBOL(scsi_print_command);



/**

 *

 *	scsi_print_status - print scsi status description

 *	@scsi_status: scsi status value

 *

drivers/scsi/hosts.c

+1 −3
Original line number Diff line number Diff line
@@ -54,8 +54,7 @@ static struct class shost_class = { 
};



/**

 *	scsi_host_set_state - Take the given host through the host

 *		state model.

 *	scsi_host_set_state - Take the given host through the host state model.

 *	@shost:	scsi host to change the state of.

 *	@state:	state to change to.

 *
@@ -431,7 +430,6 @@ EXPORT_SYMBOL(scsi_unregister); 


/**

 * scsi_host_lookup - get a reference to a Scsi_Host by host no

 *

 * @hostnum:	host number to locate

 *

 * Return value:

drivers/scsi/scsi.c

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