gnu: file-systems: Add variable %base-live-file-systems.

* gnu/system/file-systems.scm (%base-live-file-systems): New variable.
* gnu/system/install.scm (installation-os): Use %base-live-file-systems.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu/system/file-systems.scm

@@ -85,6 +85,7 @@
             %elogind-file-systems
 
             %base-file-systems
+            %base-live-file-systems
             %container-file-systems
 
             <file-system-mapping>
@@ -495,6 +496,26 @@ TARGET in the other system."
         %efivars-file-system
         %immutable-store))
 
+(define %base-live-file-systems
+  ;; This is the bare minimum to use live file-systems.
+  ;; Used in installation-os.
+  (list (file-system
+          (mount-point "/")
+          (device (file-system-label "Guix_image"))
+          (type "ext4"))
+
+        ;; Make /tmp a tmpfs instead of keeping the overlayfs.  This
+        ;; originally was used for unionfs because FUSE creates
+        ;; '.fuse_hiddenXYZ' files for each open file, and this confuses
+        ;; Guix's test suite, for instance (see
+        ;; <http://bugs.gnu.org/23056>).  We keep this for overlayfs to be
+        ;; on the safe side.
+        (file-system
+          (mount-point "/tmp")
+          (device "none")
+          (type "tmpfs")
+          (check? #f))))
+
 ;; File systems for Linux containers differ from %base-file-systems in that
 ;; they impose additional restrictions such as no-exec or need different
 ;; options to function properly.

gnu/system/install.scm

@@ -517,22 +517,7 @@ Access documentation at any time by pressing Alt-F2.\x1b[0m
     (file-systems
      ;; Note: the disk image build code overrides this root file system with
      ;; the appropriate one.
-     (cons* (file-system
-              (mount-point "/")
-              (device (file-system-label "Guix_image"))
-              (type "ext4"))
-
-            ;; Make /tmp a tmpfs instead of keeping the overlayfs.  This
-            ;; originally was used for unionfs because FUSE creates
-            ;; '.fuse_hiddenXYZ' files for each open file, and this confuses
-            ;; Guix's test suite, for instance (see
-            ;; <http://bugs.gnu.org/23056>).  We keep this for overlayfs to be
-            ;; on the safe side.
-            (file-system
-              (mount-point "/tmp")
-              (device "none")
-              (type "tmpfs")
-              (check? #f))
+     (append %base-live-file-systems
 
             ;; XXX: This should be %BASE-FILE-SYSTEMS but we don't need
             ;; elogind's cgroup file systems.