1 Notes on Linux SCSI Generic (sg) driver
2 ---------------------------------------
3 20020126
4 Introduction
5 ============
6 The SCSI Generic driver (sg) is one of the four "high level" SCSI device
7 drivers along with sd, st and sr (disk, tape and CDROM respectively). Sg
8 is more generalized (but lower level) than its siblings and tends to be
9 used on SCSI devices that don't fit into the already serviced categories.
10 Thus sg is used for scanners, CD writers and reading audio CDs digitally
11 amongst other things.
12
13 Rather than document the driver's interface here, version information
14 is provided plus pointers (i.e. URLs) where to find documentation
15 and examples.
16
17
18 Major versions of the sg driver
19 ===============================
20 There 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.
27
28
29 Sg driver documentation
30 =======================
31 The most recent documentation of the sg driver is kept at the Linux
32 Documentation Project's (LDP) site:
33 http://www.tldp.org/HOWTO/SCSI-Generic-HOWTO
34 This describes the sg version 3 driver found in the lk 2.4 series.
35 The LDP renders documents in single and multiple page HTML, postscript
36 and pdf. This document can also be found at:
37 http://www.torque.net/sg/p/sg_v3_ho.html
38
39 Documentation for the version 2 sg driver found in the lk 2.2 series can
40 be found at http://www.torque.net/sg/p/scsi-generic.txt . A larger version
41 is at: http://www.torque.net/sg/p/scsi-generic_long.txt .
42
43 The original documentation for the sg driver (prior to lk 2.2.6) can be
44 found at http://www.torque.net/sg/p/original/SCSI-Programming-HOWTO.txt
45 and in the LDP archives.
46
47 A changelog with brief notes can be found in the
48 /usr/src/linux/include/scsi/sg.h file. Note that the glibc maintainers copy
49 and edit this file (removing its changelog for example) before placing it
50 in /usr/include/scsi/sg.h . Driver debugging information and other notes
51 can be found at the top of the /usr/src/linux/drivers/scsi/sg.c file.
52
53 A more general description of the Linux SCSI subsystem of which sg is a
54 part can be found at http://www.tldp.org/HOWTO/SCSI-2.4-HOWTO .
55
56
57 Example code and utilities
58 ==========================
59 There 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
63 Both packages will work in the lk 2.4 series however sg3_utils offers more
64 capabilities. They can be found at: http://www.torque.net/sg and
65 freshmeat.net
66
67 Another approach is to look at the applications that use the sg driver.
68 These include cdrecord, cdparanoia, SANE and cdrdao.
69
70
71 Mapping of Linux kernel versions to sg driver versions
72 ======================================================
73 Here is a list of linux kernels in the 2.4 series that had new version
74 of 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
79
80 ** There were 3 changes to sg version 3.1.20 by third parties in the
81 next six linux kernel versions.
82
83 For reference here is a list of linux kernels in the 2.2 series that had
84 new 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
93
94 The lk 2.5 development series has recently commenced and it currently
95 contains sg version 3.5.23 which is functionally equivalent to sg
96 version 3.1.22 found in lk 2.4.17 .
97
98
99 Douglas Gilbert
100 26th January 2002
101 dgilbert@interlog.com
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