English
- Notes on Linux SCSI Generic (sg) driver
- ---------------------------------------
- 20020126
- Introduction
- ============
- The SCSI Generic driver (sg) is one of the four "high level" SCSI device
- drivers along with sd, st and sr (disk, tape and CDROM respectively). Sg
- is more generalized (but lower level) than its siblings and tends to be
- used on SCSI devices that don't fit into the already serviced categories.
- Thus sg is used for scanners, CD writers and reading audio CDs digitally
- amongst other things.
- Rather than document the driver's interface here, version information
- is provided plus pointers (i.e. URLs) where to find documentation
- and examples.
- Major versions of the sg driver
- ===============================
- There are three major versions of sg found in the linux kernel (lk):
- - sg version 1 (original) from 1992 to early 1999 (lk 2.2.5) .
- It is based in the sg_header interface structure.
- - sg version 2 from lk 2.2.6 in the 2.2 series. It is based on
- an extended version of the sg_header interface structure.
- - sg version 3 found in the lk 2.4 series (and the lk 2.5 series).
- It adds the sg_io_hdr interface structure.
- Sg driver documentation
- =======================
- The most recent documentation of the sg driver is kept at the Linux
- Documentation Project's (LDP) site:
- http://www.linuxdoc.org/HOWTO/SCSI-Generic-HOWTO
- This describes the sg version 3 driver found in the lk 2.4 series.
- The LDP renders documents in single and multiple page HTML, postscript
- and pdf. This document can also be found at:
- http://www.torque.net/sg/p/sg_v3_ho.html
- Documentation for the version 2 sg driver found in the lk 2.2 series can
- be found at http://www.torque.net/sg/p/scsi-generic.txt . A larger version
- is at: http://www.torque.net/sg/p/scsi-generic_long.txt .
- The original documentation for the sg driver (prior to lk 2.2.6) can be
- found at http://www.torque.net/sg/p/original/SCSI-Programming-HOWTO.txt
- and in the LDP archives.
- A changelog with brief notes can be found in the
- /usr/src/linux/include/scsi/sg.h file. Note that the glibc maintainers copy
- and edit this file (removing its changelog for example) before placing it
- in /usr/include/scsi/sg.h . Driver debugging information and other notes
- can be found at the top of the /usr/src/linux/drivers/scsi/sg.c file.
- A more general description of the Linux SCSI subsystem of which sg is a
- part can be found at http://www.linuxdoc.org/HOWTO/SCSI-2.4-HOWTO .
- Example code and utilities
- ==========================
- There are two packages of sg utilities:
- - sg3_utils for the sg version 3 driver found in lk 2.4
- - sg_utils for the sg version 2 (and original) driver found in lk 2.2
- and earlier
- Both packages will work in the lk 2.4 series however sg3_utils offers more
- capabilities. They can be found at: http://www.torque.net/sg and
- freshmeat.net
- Another approach is to look at the applications that use the sg driver.
- These include cdrecord, cdparanoia, SANE and cdrdao.
- Mapping of Linux kernel versions to sg driver versions
- ======================================================
- Here is a list of linux kernels in the 2.4 series that had new version
- of the sg driver:
- lk 2.4.0 : sg version 3.1.17
- lk 2.4.7 : sg version 3.1.19
- lk 2.4.10 : sg version 3.1.20 **
- lk 2.4.17 : sg version 3.1.22
- ** There were 3 changes to sg version 3.1.20 by third parties in the
- next six linux kernel versions.
- For reference here is a list of linux kernels in the 2.2 series that had
- new version of the sg driver:
- lk 2.2.0 : original sg version [with no version number]
- lk 2.2.6 : sg version 2.1.31
- lk 2.2.8 : sg version 2.1.32
- lk 2.2.10 : sg version 2.1.34 [SG_GET_VERSION_NUM ioctl first appeared]
- lk 2.2.14 : sg version 2.1.36
- lk 2.2.16 : sg version 2.1.38
- lk 2.2.17 : sg version 2.1.39
- lk 2.2.20 : sg version 2.1.40
- The lk 2.5 development series has recently commenced and it currently
- contains sg version 3.5.23 which is functionally equivalent to sg
- version 3.1.22 found in lk 2.4.17 .
- Douglas Gilbert
- 26th January 2002
- dgilbert@interlog.com
