I spent the better part of today's evening preparing and testing .ebuild files (available in my GitLab repository) for the so-called ‘free branch’ versions of targetcli, rtslib, and configshell called targetcli-fb, rtslib-fb, and configshell-fb. The ‘free branch’ versions are the recommended way of setting up a iSCSI target on Linux, according to the Arch Linux wiki.
In my own tests, I used my Gentoo host as iSCSI target (read: server) and a virtual machine with a fresh Debian 8 as initiator (read: client) to share a 100 MB RAM disk without any (CHAP) authentication.
Both the Gentoo and the Debian machines are using systemd as init. My package of rtslib-fb provides a .service for systemd to save/restore the target's setting on shutdown/boot.
To test the packages yourself, start by cloning the repository or manually fetch the files for the packages dev-python/rtslib-fb, dev-python/configshell-fb, and sys-block/targetcli-fb. There is already an older dev-python/rtslib-fb in the official portage tree; don't use that.
Emerge all three packages.
Follow the instructions to setup a target and initiator as you find on the Internet: Arch Linux wiki (target and initiator) or Red Hat's Storage Administration documentation (target and initiator).