User space program fileio_tgt uses interface of SCST's scst_user dev handler and allows to see how it works in various modes. Fileio_tgt provides mostly the same functionality as the kernel space SCST's scst_vdisk handler with the only exceptions that it supports O_DIRECT mode and doesn't support BLOCKIO one. O_DIRECT mode is basically the same as BLOCKIO, but also supports files, so for some loads it could be significantly faster, than the regular FILEIO access. All the words about BLOCKIO mode from SCST's README file apply to O_DIRECT mode as well.
You can find the latest development version of this handler in the SCST SVN. See the download page how to setup access to it.