githubmirror/sg3_utils

README
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Douglas Gilbert
Load sg3_utils-1.15 into trunk/.
27 июн 2007, 07:11
27 июн 2007, 07:11fcf5ebe
                      README for sg3_utils
                      ====================
Introduction
============
This package contains utilities for the Linux SCSI subsystem. In the
Linux 2.6 kernel series almost all of these programs 
will work on any devices that use the SCSI command set. Apart from SCSI 
parallel devices, ATAPI devices (CD/DVDs and tapes), USB mass storage 
devices, Fibre Channel disks and IEEE 1394 storage devices (that use 
the "SBP" protocol) use the SCSI command set.

Most utilities within the sg3_utils package work at the SCSI command
level. For example the sg_inq utility issues a SCSI INQUIRY command
and decodes the response. To view the relationship between the sg3_utils'
utility and the main SCSI command(s) that it issues see the COVERAGE file.
The only utilities that interface at a slightly higher level are sg_dd,
sgm_dd and sgp_dd. These are closely related to the Unix dd command and
typically issue a sequence of SCSI READ and WRITE commands to copy data.

Description
===========
A web site supporting the sg3_utils package, its predecessor sg_utils,
and the Linux SCSI generic driver (and the scsi_debug driver) can be
found at http://www.torque.net/sg . The most recent release version
of sg3_utils and the most recent beta is on that page. There is also
a page describing the utilities in the sg3_utils and sg_utils packages:
http://www.torque.net/sg/u_index.html . A copy of the "u_index.html"
file is in the "html" subdirectory.

In the Linux 2.4 kernel series these utilities need to use the SCSI generic
(sg) driver to access SCSI devices. The name of this package (i.e.
sg3_utils) refers to version 3 of the SCSI generic (sg) driver which
was introduced at the beginning of the 2.4 linux kernel series. Significantly
this added a new SCSI command interface structure (i.e. struct sg_io_hdr)
that is more flexible than the older "sg_header" structure found in the
sg driver in the 2.2 and earlier linux kernel series. The sg_io_hdr structure
is also more flexible than the awkward (and limiting) interface to the
SCSI_IOCTL_SEND_COMMAND ioctl supported by the linux SCSI mid level.
The version 3 sg driver also added the SG_IO ioctl that is synchronous
(i.e. it issues the requested SCSI command and waits for the response
(or a timeout) before the ioctl returns to the user space program that
invoked it). The SG_IO ioctl is now supported in other parts of the linux
kernel in the 2.6 series.

Utilities that wish to use the asynchronous SCSI command interface
(i.e. via a write() read() sequence) or issue special "commands"
(e.g. bus and device resets) still need to use the sg driver. Note
that various drivers (e.g. cdrom/sr) have different open() flag and
permissions policies that the user may need to take into account.

If you have problems or questions about them please contact the author.
Documentation for the sg device driver can be found at:
http://www.torque.net/sg/p/sg_v3_ho.html .
This is written in DocBook and the original xml can be found in the 
same directory with the ".xml" extension. Postscript and
pdf renderings are also in that directory.
Older documentation for the sg version 3 driver can be found at:
http://www.torque.net/sg/p/scsi_generic_v3.txt .

All utilities are either "GPL"-ed or have a FreeBSD license. The
intention is that users may incorporate all or part of the code in their
work as they please. Attribution is encouraged. Please check the code as
other contributors (apart from the author) may also have copyright
notices. For a list of contributors see the CREDITS file.

The "sg_lib.[hc]" files contain ASCII text corresponding to most
of the SCSI commands, errors and warning conditions. The "sg_cmds.[hc]"
files contains code to invoke common SCSI commands and associated
response processing. Both are guided by recent drafts at www.t10.org
which is the home site of SCSI (draft) standards. Since almost all
of the utilities use these files, a shared library called
"libsgutils.so" is built. Use of this library cuts down the size of the
binary distributions of sg3_utils significantly. The "Makefile" provided
in the main directory builds libsgutils.so and then builds each utility
to use that shared library. Alternatively there is a script called
"make_no_lib.sh" that will build utilities without depending on
libsgutils.so . For example "./make_no_lib.sh sg_dd" builds a version
of the sg_dd utility that does not depend on libsgutils.so .

All the utilities in the main directory have "man" pages. Additional
information (including a version number) can be found towards the top
of each ".c" file corresponding to each utility.

The sg driver in Linux can be seen as having 3 distinct versions:

   v1   lk < 2.2.6     sg_header based relatively unchanged since 1992
   v2   lk >= 2.2.6    enhanced sg_header interface structure [1999/4/16]
   v3   lk >= 2.4      additional sg_io_hdr interface structure [2001/1/4]
   v3   lk >= 2.6      same interface as found in lk 2.4 [2004/1/??]

This package is targeted as "v3" only. Another package called "sg_utils"
is targeted at "v2" and to a lesser extent "v1". The "sg_utils"
package has a subset of the utilities found in this package.

Some sg ioctls (notably SG_IO) are defined for many block devices
in lk 2.6 . In practice this means all SCSI block devices, ATAPI block devices
(mainly CD and DVD players) but _not_ ATA disks (currently). SATA disks that
use the libata kernel library accept SCSI commands and thus are supported.
Support for the SG_IO as been added to the scsi tape driver (st) in lk 2.6.6
(and support for osst and ch (medium changer) may soon follow).

No utilities in the main directory use the sg driver's older "sg_header"
interface; instead they use the newer "sg_io_hdr" interface. The "sg_io_hdr"
interface can be accessed two ways:
  - using the SG_IO ioctl [for synchronous access]
  - using a write()/read() sequence that convey instances of "sg_io_hdr"

All utilities in the main directory that issue SCSI commands use the SG_IO
ioctl except for sgp_dd.  This is due to the asynchronous nature of sgp_dd.
Note that sgp_dd does _not_ support the "blk_sgio" switch found in sg_dd.
This is important since block devices often identify themselves
(programmatically) as sg devices in lk 2.6 and it would cause serious damage
to do a write() of the sg driver's "sg_io_hdr" meta data (i.e. disk
corruption).

Warning
=======
Many devices use SCSI command sets over transport protocols not normally
associated with SCSI (as defined at http://www.t10.org ). Some of these
devices react poorly (e.g. lock up) when sent SCSI commands that they
don't support. Even sending a supported SCSI command with a field set
to an unexpected value can cause problems.

For example, all "SCSI" devices must support the INQUIRY command which
the SCSI-2 standard says should request a 36 byte response. However later
SCSI standards (e.g. SPC-2) have increased that length but some SCSI
devices lock up when they receive a request for anything other than
a 36 byte response.

Any well implemented "SCSI" device should react sensibly when a utility in
sg3_utils sends a SCSI command that it doesn't support. Unfortunately this
cannot be guaranteed.


Utilities
=========
Here is list in alphabetical order of utilities found in the main directory
of the sg3_utils directory:
  - sginfo, sgm_dd, sgp_dd, sg_dd, sg_emc_trespass, sg_get_config,
    sg_format, sg_inq, sg_logs, sg_luns, sg_map, sg_modes, sg_opcodes,
    sg_persist, sg_prevent, sg_rbuf, sg_read, sg_readcap, sg_read_long,
    sg_reassign, sg_request, sg_reset, sg_rmsn, sg_rtpg, sg_scan,
    sg_senddiag, sg_ses, sg_start, sg_sync, sg_test_rwbuff, sg_turs,
    sg_verify, sg_write_long, sg_wr_mode

These utilities and the libsgutils.so library which they depend on are built
by the Makefile in the main directory. This Makefile does not invoke the
Makefile's in the subdirectories. Each utility in the main directory has a
"man" page in section 8 (system administration commands). Binary
distributions of the sg3_utils package (e.g. "rpm" and debian packages)
typically contains the shared library, the utilities in the main directory,
their associated man pages and some documentation files (e.g. README, INSTALL,
CREDITS and COVERAGE). See the INSTALL file for instructions about building
and installing from a "tarball".

Man pages can be read (without building and installing the package) by
going to the main directory and executing something like this:
 $ man ./sg_dd.8

To see which SCSI commands (and ATA commands) are used by these
utilities see the COVERAGE file.

Here is a list in alphabetical order of utilities found in the archive
subdirectory:
  - isosize, scsi_devfs_scan, sg_debug, sgq_dd
Some of these utilities have man pages.

Here is a list in alphabetical order of utilities found in the examples
subdirectory:
  - scsi_inquiry, sg_simple1, sg_simple2, sg_simple3, sg_simple4,
    sg_simple16.c

Also in that subdirectory is a script to test sg_persist, an example
data file for sg_persist (called "transport_ids.txt") and an example
data file for sg_reassign (called "reassign_addr.txt").

The "utils" subdirectory contains source and a Makefile to build
"hxascdmp" which accepts binary data from stdin (or a file on the
command line) and outputs an ASCII-HEX and ASCII representation of
it. It is similar to the Unix od command.

The "html" subdirectory contains copies of web pages relevant to
the sg3_utils package. Currently it contains:
  - u_index.html : a description of the sg3_utils package contents
  - sg_dd.html : describes the sg_dd utility and compares it with the
                 Unix dd command
    

Notes for utilities without man pages
=====================================
The "scsi_inquiry" program shows the use of the SCSI_IOCTL_SEND_COMMAND
ioctl to send a SCSI INQUIRY command. That ioctl() is supported by the 
SCSI sub system mid level and so is common to all sd, sr, st and sg devices. 
This program has been placed in the "examples" subdirectory.

"sgq_dd" is yet another variant of dd found in the archive directory.
From the user's point of view it is very similar to sgp_dd but uses a
non-blocking state machine rather then POSIX threads for parallelism.

"sg_debug" is effectively defunct now. The user can instead do:
$ cat /proc/scsi/sg/debug . This command has been placed in the
archive directory.

"sg_simple1" and "sg_simple2" are simple example programs demonstrating
calls to the SCSI INQUIRY and TEST UNIT READY commands. They only differ
in their error processing: sg_simple1 uses sg_lib.[hc] for error
processing while sg_simple2 does its own more primitive checks.

"sg_simple3" tests out user space scatter gather added to the version 3
sg driver.

"sg_simple4" shows the INQUIRY command using mmap-ed IO to obtain its
response buffer.

"sg_simple16" attempts to send a 16 byte SCSI command, READ_16, to the
scsi device. This is only supported for lk >= 2.4.15 and for adapter
drivers that indicate that they have 16 byte CDB capability (otherwise
DID_ABORT will appear in the host_status).

Header file problems
====================
These utilities include 2 special Linux header files:
#include <scsi/sg.h>
#include <scsi/scsi.h>
These files are typically found in the directory /usr/include/scsi which
is maintained by the GNU glibc team. Unfortunately these GNU supplied
headers may not be (functionally) the same as those found in the kernel
source:
/usr/src/linux/include/scsi/sg.h   and
/usr/src/linux/include/scsi/scsi.h

If glibc and the kernel on a machine are of the same vintage then it is
probably sufficient to use the simple includes listed at the start of this
section. Another technique that used to work was to rely on
/usr/include/linux being a symbolic link to /usr/src/linux/include/linux . 
That caused the following:
#include <linux/../scsi/sg.h> 
#include <linux/../scsi/scsi.h>
to find the kernel supplied header files. However recent versions of
glibc have removed this symlink. Hence this technique is no longer
recommended.

The include file path issues are now all addressed in one file called
"sg_include.h". Please read that file.

scsirastools
============
This package found at http://scsirastools.sourceforge.net contains utilities
which overlap with the functionality offered in sg3_utils. Utilities of note
in scsirastools are:
  - sgdskfl: for loading firmware into SCSI disks
  - sgmode: get and set mode pages
  - sgdefects: list primary and grown defect lists
  - sgdiag to perform format and other test functions

plscsi
======
This is a utility which can issue arbitrary SCSI commands (i.e. supplied by
user). It is available for Linux and other operating systems.
See http://members.aol.com/plscsi .

Doug Gilbert
5th June 2005