as ZFS on Linux is still a work in progress, provide this support could make Gentoo user easier to test patch without create another ebuild this apply to sys-fs/spl and sys-fs/zfs-kmod as well Reproducible: Always
The autotools eclass provides epatch_user to us for free. There is no need to add it ourselves. Are you unable to apply patches yourself?
my fault, I didn't follow the code, I thought I have to manual add epatch_user :X