file-systems: Add 'file-system-mapping->bind-mount'.

* gnu/system/file-systems.scm (file-system-mapping->bind-mount): New
procedure.
* gnu/system/linux-container.scm (mapping->file-system): Remove.
(containerized-operating-system)[mapping->fs]: Use
'file-system-mapping->bind-mount' instead of 'mapping->file-system'.
* guix/scripts/environment.scm (launch-environment/container): Likewise.

gnu/system/file-systems.scm

@@ -63,6 +63,8 @@
             file-system-mapping-target
             file-system-mapping-writable?
 
+            file-system-mapping->bind-mount
+
             %store-mapping))
 
 ;;; Commentary:
@@ -352,6 +354,21 @@ TARGET in the other system."
   (writable? file-system-mapping-writable?        ;Boolean
              (default #f)))
 
+(define (file-system-mapping->bind-mount mapping)
+  "Return a file system that realizes MAPPING, a <file-system-mapping>, using
+a bind mount."
+  (match mapping
+    (($ <file-system-mapping> source target writable?)
+     (file-system
+       (mount-point target)
+       (device source)
+       (type "none")
+       (flags (if writable?
+                  '(bind-mount)
+                  '(bind-mount read-only)))
+       (check? #f)
+       (create-mount-point? #t)))))
+
 (define %store-mapping
   ;; Mapping of the host's store into the guest.
   (file-system-mapping

gnu/system/linux-container.scm

@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2015 David Thompson <davet@gnu.org>
-;;; Copyright © 2016 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2016, 2017 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -30,25 +30,10 @@
   #:use-module (gnu services)
   #:use-module (gnu system)
   #:use-module (gnu system file-systems)
-  #:export (mapping->file-system
-            system-container
+  #:export (system-container
             containerized-operating-system
             container-script))
 
-(define (mapping->file-system mapping)
-  "Return a file system that realizes MAPPING."
-  (match mapping
-    (($ <file-system-mapping> source target writable?)
-     (file-system
-       (mount-point target)
-       (device source)
-       (type "none")
-       (flags (if writable?
-                  '(bind-mount)
-                  '(bind-mount read-only)))
-       (check? #f)
-       (create-mount-point? #t)))))
-
 (define (containerized-operating-system os mappings)
   "Return an operating system based on OS for use in a Linux container
 environment.  MAPPINGS is a list of <file-system-mapping> to realize in the
@@ -66,7 +51,7 @@ containerized OS."
             (operating-system-file-systems os)))
 
   (define (mapping->fs fs)
-    (file-system (inherit (mapping->file-system fs))
+    (file-system (inherit (file-system-mapping->bind-mount fs))
       (needed-for-boot? #t)))
 
   (operating-system (inherit os)

guix/scripts/environment.scm

@@ -433,7 +433,8 @@ host file systems to mount inside the container."
                              (writable? #f)))
                           reqs)))
             (file-systems (append %container-file-systems
-                                  (map mapping->file-system mappings))))
+                                  (map file-system-mapping->bind-mount
+                                       mappings))))
        (exit/status
         (call-with-container file-systems
           (lambda ()