339 строки
9.4 KiB
ReStructuredText
339 строки
9.4 KiB
ReStructuredText
=====================
|
|
SCSI Interfaces Guide
|
|
=====================
|
|
|
|
:Author: James Bottomley
|
|
:Author: Rob Landley
|
|
|
|
Introduction
|
|
============
|
|
|
|
Protocol vs bus
|
|
---------------
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
The `SCSI protocol <http://www.t10.org/scsi-3.htm>`__ 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.
|
|
|
|
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,
|
|
`I2O <http://i2o.shadowconnect.com/faq.php>`__, TCP/IP
|
|
(`iSCSI <https://en.wikipedia.org/wiki/ISCSI>`__), even `Parallel
|
|
ports <http://cyberelk.net/tim/parport/parscsi.html>`__.
|
|
|
|
Design of the Linux SCSI subsystem
|
|
----------------------------------
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
SCSI upper layer
|
|
================
|
|
|
|
The upper layer supports the user-kernel interface by providing device
|
|
nodes.
|
|
|
|
sd (SCSI Disk)
|
|
--------------
|
|
|
|
sd (sd_mod.o)
|
|
|
|
sr (SCSI CD-ROM)
|
|
----------------
|
|
|
|
sr (sr_mod.o)
|
|
|
|
st (SCSI Tape)
|
|
--------------
|
|
|
|
st (st.o)
|
|
|
|
sg (SCSI Generic)
|
|
-----------------
|
|
|
|
sg (sg.o)
|
|
|
|
ch (SCSI Media Changer)
|
|
-----------------------
|
|
|
|
ch (ch.c)
|
|
|
|
SCSI mid layer
|
|
==============
|
|
|
|
SCSI midlayer implementation
|
|
----------------------------
|
|
|
|
include/scsi/scsi_device.h
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
.. kernel-doc:: include/scsi/scsi_device.h
|
|
:internal:
|
|
|
|
drivers/scsi/scsi.c
|
|
~~~~~~~~~~~~~~~~~~~
|
|
|
|
Main file for the SCSI midlayer.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi.c
|
|
:export:
|
|
|
|
drivers/scsi/scsicam.c
|
|
~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
`SCSI Common Access
|
|
Method <http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf>`__ support
|
|
functions, for use with HDIO_GETGEO, etc.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsicam.c
|
|
:export:
|
|
|
|
drivers/scsi/scsi_error.c
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Common SCSI error/timeout handling routines.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_error.c
|
|
:export:
|
|
|
|
drivers/scsi/scsi_devinfo.c
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Manage scsi_dev_info_list, which tracks blacklisted and whitelisted
|
|
devices.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_devinfo.c
|
|
:internal:
|
|
|
|
drivers/scsi/scsi_ioctl.c
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Handle ioctl() calls for SCSI devices.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_ioctl.c
|
|
:export:
|
|
|
|
drivers/scsi/scsi_lib.c
|
|
~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
SCSI queuing library.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_lib.c
|
|
:export:
|
|
|
|
drivers/scsi/scsi_lib_dma.c
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
SCSI library functions depending on DMA (map and unmap scatter-gather
|
|
lists).
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_lib_dma.c
|
|
:export:
|
|
|
|
drivers/scsi/scsi_proc.c
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
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/\*
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_proc.c
|
|
:internal:
|
|
|
|
drivers/scsi/scsi_netlink.c
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Infrastructure to provide async events from transports to userspace via
|
|
netlink, using a single NETLINK_SCSITRANSPORT protocol for all
|
|
transports. See `the original patch
|
|
submission <http://marc.info/?l=linux-scsi&m=115507374832500&w=2>`__ for
|
|
more details.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_netlink.c
|
|
:internal:
|
|
|
|
drivers/scsi/scsi_scan.c
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
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.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_scan.c
|
|
:internal:
|
|
|
|
drivers/scsi/scsi_sysctl.c
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Set up the sysctl entry: "/dev/scsi/logging_level"
|
|
(DEV_SCSI_LOGGING_LEVEL) which sets/returns scsi_logging_level.
|
|
|
|
drivers/scsi/scsi_sysfs.c
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
SCSI sysfs interface routines.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_sysfs.c
|
|
:export:
|
|
|
|
drivers/scsi/hosts.c
|
|
~~~~~~~~~~~~~~~~~~~~
|
|
|
|
mid to lowlevel SCSI driver interface
|
|
|
|
.. kernel-doc:: drivers/scsi/hosts.c
|
|
:export:
|
|
|
|
drivers/scsi/scsi_common.c
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
general support functions
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_common.c
|
|
:export:
|
|
|
|
Transport classes
|
|
-----------------
|
|
|
|
Transport classes are service libraries for drivers in the SCSI lower
|
|
layer, which expose transport attributes in sysfs.
|
|
|
|
Fibre Channel transport
|
|
~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The file drivers/scsi/scsi_transport_fc.c defines transport attributes
|
|
for Fibre Channel.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_transport_fc.c
|
|
:export:
|
|
|
|
iSCSI transport class
|
|
~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The file drivers/scsi/scsi_transport_iscsi.c defines transport
|
|
attributes for the iSCSI class, which sends SCSI packets over TCP/IP
|
|
connections.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_transport_iscsi.c
|
|
:export:
|
|
|
|
Serial Attached SCSI (SAS) transport class
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_transport_sas.c
|
|
:export:
|
|
|
|
SATA transport class
|
|
~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The SATA transport is handled by libata, which has its own book of
|
|
documentation in this directory.
|
|
|
|
Parallel SCSI (SPI) transport class
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The file drivers/scsi/scsi_transport_spi.c defines transport
|
|
attributes for traditional (fast/wide/ultra) SCSI busses.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_transport_spi.c
|
|
:export:
|
|
|
|
SCSI RDMA (SRP) transport class
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The file drivers/scsi/scsi_transport_srp.c defines transport
|
|
attributes for SCSI over Remote Direct Memory Access.
|
|
|
|
.. kernel-doc:: drivers/scsi/scsi_transport_srp.c
|
|
:export:
|
|
|
|
SCSI lower layer
|
|
================
|
|
|
|
Host Bus Adapter transport types
|
|
--------------------------------
|
|
|
|
Many modern device controllers use the SCSI command set as a protocol to
|
|
communicate with their devices through many different types of physical
|
|
connections.
|
|
|
|
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).
|
|
|
|
Debug transport
|
|
~~~~~~~~~~~~~~~
|
|
|
|
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.
|
|
|
|
To be more realistic, the simulated devices have the transport
|
|
attributes of SAS disks.
|
|
|
|
For documentation see http://sg.danny.cz/sg/sdebug26.html
|
|
|
|
todo
|
|
~~~~
|
|
|
|
Parallel (fast/wide/ultra) SCSI, USB, SATA, SAS, Fibre Channel,
|
|
FireWire, ATAPI devices, Infiniband, I2O, Parallel ports,
|
|
netlink...
|