* gnu/system.scm (operating-system-derivation)[boot-file-systems]: Keep "/".
* gnu/system/linux-initrd.scm (file-system->spec): Keep the 'check?'
flag.
(qemu-initrd)[helper-packages]: New variable. Pass it as #:to-copy.
<gexp>: Add 'set-path-environment-variable' call. Remove #:unionfs
argument for 'boot-system'.
* gnu/system/vm.scm (%linux-vm-file-systems): Add 'check?' field/
(virtualized-operating-system): Likewise for the "9p" file system.
* guix/build/linux-initrd.scm (mount-root-file-system): Change #:unionfs
default. Call 'check-file-system' before mounting ROOT, when
VOLATILE-ROOT? is false.
(check-file-system): New procedure.
(mount-file-system): Honor 'check?' element in list; add
'check-file-system' call.
(boot-system): Remove #:root-fs-type and #:unionfs parameters.
[root-mount-point?, root-fs-type]: New variables.
Call 'mount-file-system' on all MOUNTS but "/".