Prior to the emergence of Btrfs as a viable next-generation Linux file-system, Sun's ZFS file-system was sought after for Linux due to its advanced feature-set and capabilities compared to EXT3 and other open-source file-systems at the time. While ZFS support has worked its way into OpenSolaris, FreeBSD, NetBSD, and other operating systems, ZFS had not been ported to Linux as its source-code is distributed under the CDDL license, which is incompatible with the GNU GPL barring it from integration into the mainline Linux kernel. Next month, however, a working ZFS module for the Linux kernel without a dependence on FUSE will be publicly released.