Earlier versions of the sg device driver either have no version number (e.g. the original driver) or a version number starting with "2". The drivers that support this new interface have a major version number of "3". The sg version numbers are of the form "x.y.z" and the single number given by the SG_GET_VERSION_NUM ioctl() is calculated by (x * 10000 + y * 100 + z). The sg driver discussed here will yield a number greater than or equal to 30000 from SG_GET_VERSION_NUM. The version number can also be seen using cat /proc/scsi/sg/version in the new driver. This document describes sg version 3.1.24 for the lk 2.4 series. Where some facility has been added during the lk 2.4 series (e.g. mmap-ed IO) and hence is not available in all versions of the lk 2.4 series, this is noted. 
Here is a list of sg versions that have appeared to date during the lk 2.4 series.
lk 2.4.0 : sg version 3.1.17
lk 2.4.7 : sg version 3.1.19 [see include/scsi/sg.h in that or a later version for the changelog]
lk 2.4.10 : sg version 3.1.20 [This version had several changes put into it by third parties over the next 6 release kernel versions.]
lk 2.4.17 : sg version 3.1.22
lk 2.4.19 : sg version 3.1.24 [lk 2.4.19 hasn't been released at the time of writing. It will most likely contains sg version 3.1.24 .]
There is an sg version 3.0.19 which is an optional driver for the lk 2.2 series. It has the following limitations: