The Linux SCSI Generic (sg) Driver

  1. The Linux SCSI Generic (sg) Driver

    1. News

    2. Introduction

    3. Background

    4. Features

    5. SG device driver downloads

    6. Utilities: sg3_utils and sg_utils

    7. Sg related pages

    8. External references

News

[2018-11-27] early beta of sg3_utils version 1.45 (rev796) . Bug fixes and more testing utilities, see ChangeLog.

[2018-09-12] release of sg3_utils version 1.44 . See sg3_utils page. The git mirror for sg3_utils contains a release tag for version 1.43 from 2016. So this release (1.44) contains minimal changes from yesterday and should remove any confusion.

[2018-09-11] release of sg3_utils version 1.43 . See sg3_utils page.

[2018-07-31] sg3_utils-1.43 rev 785 tarball, see sg3_utils page; sdparm-1.11 rev 320 tarball, see sdparm page, ddpt-0.96 rev 363, see ddpt page. https://github.com/doug-gilbert mirrors for sdparm and ddpt updated.

[2018-07-20] lsscsi-0.30 released, see lsscsi page.

[2018-05-26] The author's various SCSI related packages are now mirrored on github.com . The primary repositories remain in subversion on the author's equipment. The sg3_utils and lsscsi packages are mirrored on Hannes Reinecke's site at github : https://github.com/hreinecke/sg3_utils in the master (default) branch. The author continues to track progress with a subversion revision number which is a sequential number currently at 774 for sg3_utils. The github sg3_utils package's ChangeLog file shows where the mirror is "at" and currently that is revision 742 xxxxx dated 20180102, several commits behind the author's repository. The other sg3_utils git branches may be of interest to users and relate to Hannes' work at SUSE Labs. Most work in those other branches will be merged into the master branch in time. Also found at that location is the lsscsi mirror. Both packages may have later versions on this site (as tarballs in the Downloads section of the links given above). So it might be worthwhile to check both locations.

The author also has a github account at https://github.com/doug-gilbert which has mirrors for sdparm, ddpt and smp_utils packages. Since sdparm and ddpt depend on a library from sg3_utils, a partial package called sg3_utils_lib is also there. sg3_utils_lib only contains the lib/ and include/ sub-directories from the sg3_utils package. Currently sg3_utils_lib corresponds to version 774 of the author's sg3_utils subversion repository and the sdparm and ddpt packages assume that revision. So it is better to build sdparm and ddpt with sg3_utils_lib than with Hannes' sg3_utils repository (because it is currently two revisions behind).

So, for example to build sdparm, clone the github sdparm and sg3_utils_lib repositories to the build machine; then from sg3_utils_lib clone, copy the include/ and lib/ directories with those names and contents over to the sdparm clone, under the main directory. So that main directory should end up at least containing these sub-directories: src/, doc/, lib/ and include/. The sdparm package should be then ready to build. IMO, contrary to much online propaganda, git is not better in all respects than subversion, especially for non-distributed development. In this case the author uses subversion's "externals" feature to include the library sub-tree of sg3_utils in the source trees of sdparm and ddpt. There is no exact parallel to this feature in git.

Packages will still have major releases done through this site. For example, that will be release 1.43 for sg3_utils . The release will be source tarballs and Debian and Redhat packages for Linux. There will also be a tarball of Windows executable(s) typically built with MinGW. Also there is an attempt to publicise the releases on related newsgroups (e.g. Note that the subversion revision number stops increasing in the ChangeLog once a release has been made, and a new paragraph will appear at the top of the ChangeLog when revisions are committed for the next release.


[2014-09-30] update tools page: brief summary of various storage/scsi tools
[2010-09-13] add device naming page
[2008-10-01] sg pages find a new home at http://sg.danny.cz/sg/

Introduction

The Linux sg driver is a upper level SCSI subsystem device driver that is used primarily to handle devices _not_ covered by the other upper level drivers: sd (disks), st (tapes) and sr (CDROMs and DVDs). The sg driver is used for enclosure management, cd writers, applications that read cd audio digitally and scanners. Sg can also be used for less usual tasks performed on disks, tapes and cdroms. Sg is a character device driver which, in some contexts, gives it advantages over block device drivers such as sd and sr. The interface of sg is at the level of SCSI command requests and their associated responses.

The term SCSI has several meaning depending on the context. This leads to confusion. One practical way of defining it today is everything that the T10 INCITS committee controls, see www.t10.org . Probably the most succinct overview is this standards architecture page . For practical purposes a "SCSI device" in Linux is any device that uses the Linux SCSI subsystem and this often includes SATA disks.

From about Linux kernel 2.6.24, there is an alternate SCSI pass-through driver called "bsg" (block SCSI generic driver). The bsg driver has device names of the form /dev/bsg/0:1:2:3 and supports the SG_IO ioctl with the sg version 3 interface. The bsg driver also supports the sg version 4 interface which at this time the sg driver does not. Amongst other improvements the sg version 4 interface supports SCSI bidirectional commands. All recent "sg" user space packages (i.e. sg3_utils, sdparm, ddpt and smp_utils) work equally well on both sg and bsg device names.

Background

The original driver was written by Lawrence Foard in 1992 and remained unchanged for several years. In August 1998 Heiko Eissfeldt and Joerg Schilling started working on enhancements to this driver. Soon after, the author became involved and these efforts culminated in a new sg driver being placed in Linux kernel 2.2.6 which was released on 16th April 1999. It contains the first major upgrade to the SCSI generic packet device driver ("sg") since 1992. This new driver has a super-set of the original interface and the semantics of the implementation are very similar. Hence it offers a high degree of backward compatibility with the original driver.

The major reason for introducing a new sg driver into the 2.2 series of kernels was the problem that the original device driver was having finding memory. This driver improves the situation by using scatter gather, memory above the 16 MBytes level and memory from the scsi dma pool as appropriate. Other drivers were affected by these memory problems (especially those associated with ISA hardware). In kernel 2.2.10 H.J. Lu introduced a new kernel memory allocator that alleviated many of these memory problems.

On 4th January 2001 the Linux 2.4.0 kernel was introduced and it contained the "version 3" sg driver that is described below.

On 17th December 2003 the Linux 2.6.0 kernel was introduced and it also contained the "version 3" sg driver that is described below. The SG_IO ioctl was implemented in the block layer and in several other "char" SCSI drivers (e.g. the st driver for tapes). Hence many programs can use primary device nodes (e.g. /dev/hdd for an ATAPI cd/dvd writer) to send SCSI command via the SG_IO ioctl. The sg driver still permits a clean pass through interface to all devices that use the Linux SCSI subsystem.

Features

The following enhancements have been added (in lk 2.2.6): scatter gather, command queueing, per file descriptor sequencing (was per device) and asynchronous notification. Scatter gather allows large buffers (previously limited to 128 KB on i386) to be used. Scatter gather is also a lot more "kernel friendly". The original driver used a single large buffer which made it impossible to run 2 or more sg-based applications at the same time. With the new driver a buffer is reserved for each file descriptor guaranteeing that at least that buffer size will be available for each request on the file descriptor. A user may request a larger buffer size on any particular request but runs the (usually remote) risk of an out of memory (ENOMEM) error.

A "version 3" sg driver was introduced in Linux kernel 2.4.0 . It adds a new interface that allows more control over SCSI commands and returns more information about their performance. This driver is present in Linux kernel 2.4.0 . A separate version with reduced capabilities is available for the 2.2 series kernels. Features include: a simplified SG_IO ioctl, larger sense buffer, residual DMA count, 16 byte (or longer) commands, direct IO support, command duration timing and a "proc_fs" interface. Naturally it is backward compatible with applications based on the sg interface in the lk 2.2 series and earlier.

In the lk 2.6 series the SG_IO ioctl has been replicated (with a slightly reduced feature set) in the block subsystem. This allows the SG_IO ioctl to be used on block devices such as /dev/sda and /dev/scd0. In lk 2.6.6 the SG_IO ioctl became available in the st upper level SCSI subsystem driver (for tapes). See the sg_io page.

SG device driver downloads

The following table summarizes the different versions of the sg device driver that are available. If you wish to use one of these tarballs then untar it in /usr/src/linux (or wherever the top of your kernel tree is). As a precaution you may wish to copy the files include/scsi/sg.h and drivers/scsi/sg.c to other names. This will facilitate reversing the patch if required. For information about the differences between versions see the history section at the top of the include/scsi/sg.h file.

  Table 1. sg device drivers

Sg driver 
version+tarball

Notes

sg version  3.0.19

sg version 3 backported to lk 2.2

sg version  1.5.01

sg version 1 (original) ported to lk 2.4

 

 

sg3117_lk240

documentation and notes

sg_lk2422

bug fix

sg_lk2423

bug fix, found in lk 2.4.23->26

sg_lk2428

version found in lk 2.4.28

sg_lk2429

version found in lk 2.4.29,30,31,32

 

  

sg_lk2611

 driver found in 2.6.11

sg_lk2613

 driver found in 2.6.13

sg_lk2616

driver found in 2.6.16

sg_lk2618

driver found in 2.6.18

sg_lk2618scat

proposed additions including scatter_elem_sz attribute


For the Linux kernel 2.2 series, the current  production version of the sg driver is 2.1.39 . All sg drivers for the 2.2 series of kernels (including the original) are interchangeable (but see final section on this page about Red Hat 6.2 and Mandrake 7.1). So, for example, sg22orig.tgz can be put in lk 2.2.17 while, on the other hand, sg2140.tgz can be put in lk 2.2.0 .

For the Linux kernel 2.4 series, the current production version of sg is 3.1.25 (in lk 2.4.23->32).

For the Linux kernel 2.6 series, the current production version of sg is 3.5.34 .

Older versions can be obtained from this directory. A sub directory called "original" contains the original driver (i.e. prior to linux kernel 2.2.6) and its HOWTO document.

Utilities: sg3_utils and sg_utils

These packages contain multiple utilities, all with command line interfaces. They send one one more SCSI commands to the nominated device and output the response including error reports if the command failed. The name of the SCSI command executed is typically reflected in the name of the utility; for example: "sg_inq" sends a SCSI INQUIRY command and decodes its response. These utilities were originally written for the Linux operating system. In sg3_utils version 1.19 a subset of the utilities were ported to FreeBSD and Tru64; in version 1.22 a similar subset of the utilities were ported to Windows; and in version 1.24 a Solaris port was added.

The most recent package is called sg3_utils and it uses the sg "version 3" interface (sometimes known as the SG_IO interface) in linux. This interface is in  lk 2.4.0 and later kernels, including the lk 2.6, 3 and 4 series. All new features are being added into sg3_utils (i.e. it is still  being actively developed). Many of the utilities in sg3_utils (versions >= 1.02) can be used directly on block devices (e.g. sg_inq /dev/sda) in the lk 2.6 series.  The sg_dd utility is at a slightly higher level issuing SCSI READ and WRITE commands to copy data, mimicking the Unix dd command. See the sg3_utils package page for more details.

The older (and original) package is called sg_utils and it uses the sg version 2 interface found linux kernel version 2.2.6 and onward. Over half of those utilities will also work on the original sg device driver (at least back to the lk 2.0 series). If required, "make common" will produce the subset that will work on the whole lk 2.x series. Since the sg "version 3" device driver still maintains the original interface, the sg_utils package will continue to work in the lk 2.4 and lk 2.6 series . This package is now in maintenance mode, only bugs will be fixed. See this page for more details.

The latest versions, packaged in tarballs, source, binary rpms and debian packages are given in the following table. They contain README and CHANGELOG files and man pages.  The tarball contains a "spec" file for building rpms and a debian directory containing build information.  Here is the most recently released sg3_utils CHANGELOG .

 
Table 2. sg3_utils/sg_utils tarballs and packages


  tarballs 

rpm source rpms

i386 rpm binaries

   debian packages

sg3_utils
check News
section above
for betas

sg3_utils-1.44.tgz
sg3_utils-1.44.tar.xz



sg3-utils_1.44-0.1_amd64.deb
libsgutils2-2_1.44-0.1_amd64.deb

sg_utils

sg_utils-1.02.tgz

sg_utils-1.02-1.src.rpm

sg_utils-1.02-1.i386.rpm



See the sg3_utils page for more packages (e.g. 64 bit versions of Debian, Redhat and Windows binary packages) plus older versions.

Sg related pages

Following are some links to related pages on this site:

External references

Here are some useful links to related information held at other sites:

Douglas Gilbert can be emailed at that address.
Last updated: 27th November 2018,  14:00 [UTC-5]