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diff --git a/Documentation/scsi/scsi-generic.txt b/Documentation/scsi/scsi-generic.txt new file mode 100644 index 00000000000..c38e2b3648e --- /dev/null +++ b/Documentation/scsi/scsi-generic.txt @@ -0,0 +1,101 @@ + 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.tldp.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.tldp.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 |