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| |
| <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> |
