bcachefs is a next generation, robust, high performance Linux filesystem supporting CoW, device tiering, compression, and encryption.
Presently bcachefs is not ready to be distributed in the upstream Linux kernel. Those who are interested in using bcachefs must patch the Linux kernel in order to add support.
Obtain the patched kernels sources.
Right now it is easier for bcachefs' developer Ken Overstreet to maintain kernel sources with the bcachefs already applied.
Move to the kernel sources directory on Gentoo, then clone the sources (dev-vcs/git is required):
git clone --depth=1 https://evilpiepirate.org/git/bcachefs.git bcachefs.git
Build the kernel
The bcachefs kernel sources will need to be built. With the exceptions of defining any new kernel features and enabling CONFIG_BCACHE_FS, the kernel can be built using the currently running kernel's configuration:
zcat /proc/config.gz > /usr/src/bcachefs.git/.config
Build (and install) the kernel, then update the bootloader (GRUB2 presumed):
make && make install
grub-mkconfig -o /boot/grub/grub.cfg
There are presently no USE flags for the sys-fs/bcache-tools package, so simply emerge the package:
emerge --ask sys-fs/bcache-tools
This is for bcache-tools package which is associated with hybrid hard drives. This package has been requested with a proposed ebuild via bug #657120.