If you need a particular rootfs for an ARM7 or ARM64 device, there is a source of these at http://libguestfs.org/download/builder/
As an example, for Fedora 23 aarch64, then download the http://libguestfs.org/download/builder/fedora-23-aarch64.xz file, and then expand it (I use ark..) This will give you a file fedora-23-aarch64, and simply rename this to fedora-23-aarch64.img.
As the Fedora aarch64 images are (at present..) intended for servers, the image includes a FAT EFI partition, followed by an EXT4 boot partition, followed by a SWAP partition, followed by the the actual rootfs partition, which is in XFS format… These images are designed for use with QEMU etc., after all.. Most of my ARM devices use U-Boot with a FAT boot partition, rather than EFI, and it is relatively easy to create your own EXT4 partition on an SDcard, and then just copy the contents of the XFS rootfs across..
As you can see, the image partitions can be easily mounted locally, using the Gnome Disks utility.. The menu for this function is somewhat hidden, but is accessed by clicking on the little radio-button in the top left..
Robert Gadsdon. April 25, 2016.