1            Notes on Linux SCSI Generic (sg) driver
   2            ---------------------------------------
   3                                                        20020126
   6The SCSI Generic driver (sg) is one of the four "high level" SCSI device
   7drivers along with sd, st and sr (disk, tape and CDROM respectively). Sg
   8is more generalized (but lower level) than its siblings and tends to be
   9used on SCSI devices that don't fit into the already serviced categories.
  10Thus sg is used for scanners, CD writers and reading audio CDs digitally
  11amongst other things.
  13Rather than document the driver's interface here, version information
  14is provided plus pointers (i.e. URLs) where to find documentation
  15and examples.
  18Major versions of the sg driver
  20There are three major versions of sg found in the linux kernel (lk):
  21      - sg version 1 (original) from 1992 to early 1999 (lk 2.2.5) . 
  22        It is based in the sg_header interface structure.
  23      - sg version 2 from lk 2.2.6 in the 2.2 series. It is based on
  24        an extended version of the sg_header interface structure.
  25      - sg version 3 found in the lk 2.4 series (and the lk 2.5 series).
  26        It adds the sg_io_hdr interface structure.
  29Sg driver documentation
  31The most recent documentation of the sg driver is kept at the Linux
  32Documentation Project's (LDP) site: 
  34This describes the sg version 3 driver found in the lk 2.4 series.
  35The LDP renders documents in single and multiple page HTML, postscript
  36and pdf. This document can also be found at:
  39Documentation for the version 2 sg driver found in the lk 2.2 series can
  40be found at A larger version
  41is at:
  43The original documentation for the sg driver (prior to lk 2.2.6) can be
  44found at
  45and in the LDP archives.
  47A changelog with brief notes can be found in the
  48/usr/src/linux/include/scsi/sg.h file. Note that the glibc maintainers copy 
  49and edit this file (removing its changelog for example) before placing it 
  50in /usr/include/scsi/sg.h . Driver debugging information and other notes 
  51can be found at the top of the /usr/src/linux/drivers/scsi/sg.c file.
  53A more general description of the Linux SCSI subsystem of which sg is a 
  54part can be found at .
  57Example code and utilities
  59There are two packages of sg utilities:
  60  - sg3_utils   for the sg version 3 driver found in lk 2.4
  61  - sg_utils    for the sg version 2 (and original) driver found in lk 2.2
  62                and earlier
  63Both packages will work in the lk 2.4 series however sg3_utils offers more
  64capabilities. They can be found at: and
  67Another approach is to look at the applications that use the sg driver.
  68These include cdrecord, cdparanoia, SANE and cdrdao.
  71Mapping of Linux kernel versions to sg driver versions
  73Here is a list of linux kernels in the 2.4 series that had new version
  74of the sg driver:
  75      lk 2.4.0 : sg version 3.1.17
  76      lk 2.4.7 : sg version 3.1.19 
  77      lk 2.4.10 : sg version 3.1.20  **
  78      lk 2.4.17 : sg version 3.1.22 
  80** There were 3 changes to sg version 3.1.20 by third parties in the
  81   next six linux kernel versions.
  83For reference here is a list of linux kernels in the 2.2 series that had 
  84new version of the sg driver:
  85      lk 2.2.0 : original sg version [with no version number]
  86      lk 2.2.6 : sg version 2.1.31
  87      lk 2.2.8 : sg version 2.1.32
  88      lk 2.2.10 : sg version 2.1.34 [SG_GET_VERSION_NUM ioctl first appeared]
  89      lk 2.2.14 : sg version 2.1.36
  90      lk 2.2.16 : sg version 2.1.38
  91      lk 2.2.17 : sg version 2.1.39
  92      lk 2.2.20 : sg version 2.1.40
  94The lk 2.5 development series has recently commenced and it currently
  95contains sg version 3.5.23 which is functionally equivalent to sg
  96version 3.1.22 found in lk 2.4.17 .
  99Douglas Gilbert
 10026th January 2002
 102 kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.