mkinitcpio-btrfs.install

post_install() { post_upgrade "${@}"; }

post_upgrade() {

    { grep -qe '^HOOKS=.*btrfs[^_]' /etc/mkinitcpio.conf && cat <<'MSG'

==> WARNING: detected active hook "btrfs" in /etc/mkinitcpio.conf
  -> You MUST rename it to "btrfs_advanced".
     Else this hook will *not* run!
MSG
} || {
    [ -z "${2}" ] && ! grep -qe '^HOOKS=.*btrfs_advanced' /etc/mkinitcpio.conf && cat <<'MSG'

==> Add hook to /etc/mkinitcpio.conf:
  -> HOOKS="[...] btrfs_advanced"
MSG
}

    cat <<'MSG'

==> Have a look in /etc/default/btrfs_advanced to configure advanced options.

==> Run mkinitcpio to update your initramfs image
    # mkinitcpio -p linux

==> ATTENTION: GRUB 2.02 does no longer support relative paths from set-default
    subvolumes. Thus it is recommended to regenerate your GRUB configuration
    using grub-mkconfig and also reinstall GRUB to your drive using
    grub-install, as this is not done automatically on GRUB version updates.
MSG

    [ $(vercmp ${1} 0.3) -ge 0 ] &&
    [ $(vercmp ${2:-0} 0.3) -lt 0 ] &&
        _display_rollback_add_info

    cat <<'MSG'

==> Have ideas for this hook? Share!
  -> [GitHub] https://github.com/xtfxme/mkinitcpio-btrfs
  -> [AUR]    https://aur.archlinux.org/packages/mkinitcpio-btrfs
MSG

    echo
}

post_remove() {

    cat <<'MSG'

==> Remove "btrfs_advanced" from HOOKS in /etc/mkinitcpio.conf

==> Run mkinitcpio to update your initramfs image (remove hook)
    # mkinitcpio -p linux
MSG

    echo
}

_display_rollback_add_info() {

    cat <<'MSG'

==> To ENABLE rollback support, EITHER:
  -> Reboot and the hook will ask to do it for you.
  -> Or run the following command RIGHT before rebooting:
     # btrfs subvolume snapshot / /__active
     # btrfs subvolume list /
     ID 256 gen 98 top level 5 path __active
     # btrfs subvolume set-default 256 .
     Changes between snapshot and reboot will be ignored!
MSG

}