57d1c23f98
Recently wikipedia announced to secure access to the servers. Now all http access re-route to https. Signed-off-by: Masanari Iida <standby24x7@gmail.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
410 lines
14 KiB
XML
410 lines
14 KiB
XML
<?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 Interfaces Guide</title>
|
|
|
|
<authorgroup>
|
|
<author>
|
|
<firstname>James</firstname>
|
|
<surname>Bottomley</surname>
|
|
<affiliation>
|
|
<address>
|
|
<email>James.Bottomley@hansenpartnership.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='https://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&m=115507374832500&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 management
|
|
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://sg.danny.cz/sg/sdebug26.html'>http://sg.danny.cz/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>
|