system: Add '%devtmpfs-file-system' for udev, and '%base-file-systems'.

Suggested by Adam Pribyl <pribyl@lowlevel.cz>.

* gnu/services/base.scm (udev-service)[requirement]: Add
  'file-system-/dev'.
* gnu/system/file-systems.scm (%devtmpfs-file-system,
  %base-file-systems): New variables.
* gnu/system/install.scm (installation-services)[file-systems]: Use
  %base-file-systems.
* build-aux/hydra/demo-os.scm (file-systems): Likewise.
* doc/guix.texi (System Installation): Show %BASE-FILE-SYSTEMS in the
  example.
  (Using the Configuration System): Likewise.
  (File Systems): Document %base-file-systems, %devtmpfs-file-system,
  %binary-format-file-system, and %fuse-control-file-system.

1 files changed, 7 insertions, 7 deletions

diff --git a/build-aux/hydra/demo-os.scm b/build-aux/hydra/demo-os.scm
index 89b67aabe3..9164500d70 100644
--- a/build-aux/hydra/demo-os.scm
+++ b/build-aux/hydra/demo-os.scm
@@ -44,13 +44,13 @@
  (file-systems
   ;; We provide a dummy file system for /, but that's OK because the VM build
   ;; code will automatically declare the / file system for us.
-  (list (file-system
-          (mount-point "/")
-          (device "dummy")
-          (type "dummy"))
-        ;; %fuse-control-file-system   ; needs fuse.ko
-        ;; %binary-format-file-system  ; needs binfmt.ko
-        ))
+  (cons* (file-system
+           (mount-point "/")
+           (device "dummy")
+           (type "dummy"))
+         ;; %fuse-control-file-system   ; needs fuse.ko
+         ;; %binary-format-file-system  ; needs binfmt.ko
+         %base-file-systems))
 
  (users (list (user-account
                (name "guest")