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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:04 EST.

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://sg.danny.cz/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://sg.danny.cz/sg/. A larger version
41	is at: http://sg.danny.cz/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://sg.danny.cz/sg/sg3_utils.html and 
65	freecode.com
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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