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118 lines
4.3 KiB
118 lines
4.3 KiB
.. SPDX-License-Identifier: GPL-2.0 |
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Notes on Linux SCSI Generic (sg) driver |
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20020126 |
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Introduction |
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============ |
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The SCSI Generic driver (sg) is one of the four "high level" SCSI device |
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drivers along with sd, st and sr (disk, tape and CDROM respectively). Sg |
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is more generalized (but lower level) than its siblings and tends to be |
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used on SCSI devices that don't fit into the already serviced categories. |
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Thus sg is used for scanners, CD writers and reading audio CDs digitally |
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amongst other things. |
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Rather than document the driver's interface here, version information |
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is provided plus pointers (i.e. URLs) where to find documentation |
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and examples. |
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Major versions of the sg driver |
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=============================== |
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There are three major versions of sg found in the linux kernel (lk): |
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- sg version 1 (original) from 1992 to early 1999 (lk 2.2.5) . |
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It is based in the sg_header interface structure. |
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- sg version 2 from lk 2.2.6 in the 2.2 series. It is based on |
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an extended version of the sg_header interface structure. |
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- sg version 3 found in the lk 2.4 series (and the lk 2.5 series). |
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It adds the sg_io_hdr interface structure. |
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Sg driver documentation |
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======================= |
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The most recent documentation of the sg driver is kept at the Linux |
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Documentation Project's (LDP) site: |
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- http://www.tldp.org/HOWTO/SCSI-Generic-HOWTO |
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This describes the sg version 3 driver found in the lk 2.4 series. |
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The LDP renders documents in single and multiple page HTML, postscript |
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and pdf. This document can also be found at: |
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- http://sg.danny.cz/sg/p/sg_v3_ho.html |
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Documentation for the version 2 sg driver found in the lk 2.2 series can |
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be found at http://sg.danny.cz/sg/. A larger version |
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is at: http://sg.danny.cz/sg/p/scsi-generic_long.txt. |
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The original documentation for the sg driver (prior to lk 2.2.6) can be |
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found at http://www.torque.net/sg/p/original/SCSI-Programming-HOWTO.txt |
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and in the LDP archives. |
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A changelog with brief notes can be found in the |
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/usr/src/linux/include/scsi/sg.h file. Note that the glibc maintainers copy |
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and edit this file (removing its changelog for example) before placing it |
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in /usr/include/scsi/sg.h . Driver debugging information and other notes |
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can be found at the top of the /usr/src/linux/drivers/scsi/sg.c file. |
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A more general description of the Linux SCSI subsystem of which sg is a |
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part can be found at http://www.tldp.org/HOWTO/SCSI-2.4-HOWTO . |
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Example code and utilities |
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========================== |
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There are two packages of sg utilities: |
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========= ========================================================== |
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sg3_utils for the sg version 3 driver found in lk 2.4 |
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sg_utils for the sg version 2 (and original) driver found in lk 2.2 |
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and earlier |
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========= ========================================================== |
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Both packages will work in the lk 2.4 series however sg3_utils offers more |
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capabilities. They can be found at: http://sg.danny.cz/sg/sg3_utils.html and |
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freecode.com |
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Another approach is to look at the applications that use the sg driver. |
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These include cdrecord, cdparanoia, SANE and cdrdao. |
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Mapping of Linux kernel versions to sg driver versions |
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====================================================== |
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Here is a list of linux kernels in the 2.4 series that had new version |
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of the sg driver: |
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- lk 2.4.0 : sg version 3.1.17 |
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- lk 2.4.7 : sg version 3.1.19 |
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- lk 2.4.10 : sg version 3.1.20 [#]_ |
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- lk 2.4.17 : sg version 3.1.22 |
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.. [#] There were 3 changes to sg version 3.1.20 by third parties in the |
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next six linux kernel versions. |
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For reference here is a list of linux kernels in the 2.2 series that had |
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new version of the sg driver: |
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- lk 2.2.0 : original sg version [with no version number] |
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- lk 2.2.6 : sg version 2.1.31 |
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- lk 2.2.8 : sg version 2.1.32 |
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- lk 2.2.10 : sg version 2.1.34 [SG_GET_VERSION_NUM ioctl first appeared] |
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- lk 2.2.14 : sg version 2.1.36 |
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- lk 2.2.16 : sg version 2.1.38 |
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- lk 2.2.17 : sg version 2.1.39 |
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- lk 2.2.20 : sg version 2.1.40 |
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The lk 2.5 development series has recently commenced and it currently |
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contains sg version 3.5.23 which is functionally equivalent to sg |
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version 3.1.22 found in lk 2.4.17. |
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Douglas Gilbert |
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26th January 2002 |
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[email protected]
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