LXR linux/Documentation/scsi/scsi-generic.rst

   1.. SPDX-License-Identifier: GPL-2.0
   2
   3=======================================
   4Notes on Linux SCSI Generic (sg) driver
   5=======================================
   6
   7                                                        20020126
   8
   9Introduction
  10============
  11The SCSI Generic driver (sg) is one of the four "high level" SCSI device
  12drivers along with sd, st and sr (disk, tape and CDROM respectively). Sg
  13is more generalized (but lower level) than its siblings and tends to be
  14used on SCSI devices that don't fit into the already serviced categories.
  15Thus sg is used for scanners, CD writers and reading audio CDs digitally
  16amongst other things.
  17
  18Rather than document the driver's interface here, version information
  19is provided plus pointers (i.e. URLs) where to find documentation
  20and examples.
  21
  22
  23Major versions of the sg driver
  24===============================
  25There are three major versions of sg found in the linux kernel (lk):
  26      - sg version 1 (original) from 1992 to early 1999 (lk 2.2.5) .
  27        It is based in the sg_header interface structure.
  28      - sg version 2 from lk 2.2.6 in the 2.2 series. It is based on
  29        an extended version of the sg_header interface structure.
  30      - sg version 3 found in the lk 2.4 series (and the lk 2.5 series).
  31        It adds the sg_io_hdr interface structure.
  32
  33
  34Sg driver documentation
  35=======================
  36The most recent documentation of the sg driver is kept at the Linux
  37Documentation Project's (LDP) site:
  38
  39- http://www.tldp.org/HOWTO/SCSI-Generic-HOWTO
  40
  41This describes the sg version 3 driver found in the lk 2.4 series.
  42
  43The LDP renders documents in single and multiple page HTML, postscript
  44and pdf. This document can also be found at:
  45
  46- http://sg.danny.cz/sg/p/sg_v3_ho.html
  47
  48Documentation for the version 2 sg driver found in the lk 2.2 series can
  49be found at http://sg.danny.cz/sg/. A larger version
  50is at: http://sg.danny.cz/sg/p/scsi-generic_long.txt.
  51
  52The original documentation for the sg driver (prior to lk 2.2.6) can be
  53found at http://www.torque.net/sg/p/original/SCSI-Programming-HOWTO.txt
  54and in the LDP archives.
  55
  56A changelog with brief notes can be found in the
  57/usr/src/linux/include/scsi/sg.h file. Note that the glibc maintainers copy
  58and edit this file (removing its changelog for example) before placing it
  59in /usr/include/scsi/sg.h . Driver debugging information and other notes
  60can be found at the top of the /usr/src/linux/drivers/scsi/sg.c file.
  61
  62A more general description of the Linux SCSI subsystem of which sg is a
  63part can be found at http://www.tldp.org/HOWTO/SCSI-2.4-HOWTO .
  64
  65
  66Example code and utilities
  67==========================
  68There are two packages of sg utilities:
  69
  70    =========   ==========================================================
  71    sg3_utils   for the sg version 3 driver found in lk 2.4
  72    sg_utils    for the sg version 2 (and original) driver found in lk 2.2
  73                and earlier
  74    =========   ==========================================================
  75
  76Both packages will work in the lk 2.4 series however sg3_utils offers more
  77capabilities. They can be found at: http://sg.danny.cz/sg/sg3_utils.html and
  78freecode.com
  79
  80Another approach is to look at the applications that use the sg driver.
  81These include cdrecord, cdparanoia, SANE and cdrdao.
  82
  83
  84Mapping of Linux kernel versions to sg driver versions
  85======================================================
  86Here is a list of linux kernels in the 2.4 series that had new version
  87of the sg driver:
  88
  89     - lk 2.4.0 : sg version 3.1.17
  90     - lk 2.4.7 : sg version 3.1.19
  91     - lk 2.4.10 : sg version 3.1.20 [#]_
  92     - lk 2.4.17 : sg version 3.1.22
  93
  94.. [#] There were 3 changes to sg version 3.1.20 by third parties in the
  95       next six linux kernel versions.
  96
  97For reference here is a list of linux kernels in the 2.2 series that had
  98new version of the sg driver:
  99
 100     - lk 2.2.0 : original sg version [with no version number]
 101     - lk 2.2.6 : sg version 2.1.31
 102     - lk 2.2.8 : sg version 2.1.32
 103     - lk 2.2.10 : sg version 2.1.34 [SG_GET_VERSION_NUM ioctl first appeared]
 104     - lk 2.2.14 : sg version 2.1.36
 105     - lk 2.2.16 : sg version 2.1.38
 106     - lk 2.2.17 : sg version 2.1.39
 107     - lk 2.2.20 : sg version 2.1.40
 108
 109The lk 2.5 development series has recently commenced and it currently
 110contains sg version 3.5.23 which is functionally equivalent to sg
 111version 3.1.22 found in lk 2.4.17.
 112
 113
 114Douglas Gilbert
 115
 11626th January 2002
 117
 118dgilbert@interlog.com
 119