env: Add environment-mounted?

env.scm

@@ -1,6 +1,7 @@
 (define-module (env)
   #:use-module (gcrypt hash)
   #:use-module (guix base32)
+  #:use-module (guix build syscalls)
   #:use-module (guix build utils)
   #:use-module (guix hash)
   #:use-module (ice-9 ftw)
@@ -38,7 +39,8 @@
             remove-env-no-checks!
             roll-back!
             environment->overlay-mount-maybe
-            unmount-environment))
+            unmount-environment
+            environment-mounted?))
 
 (define directory-files (@@ (ice-9 ftw) directory-files))
 
@@ -439,6 +441,21 @@ by other environments made."
     (when (file-exists? tmpdirln)
       (delete-file tmpdirln))))
 
+(define (fuse-overlayfs-mounts)
+  (filter (λ (m) (equal? "fuse.fuse-overlayfs"
+                         (mount-type m) ))
+          (mounts)))
+
+(define (fuse-overlayfs-mount-points)
+  (map mount-point (fuse-overlayfs-mounts)))
+
+(define (environment-mounted? env)
+  (if (member  (string-append %env-directory
+                              "/" (symbol->string (environment-name env)))
+               (fuse-overlayfs-mount-points))
+      #t
+      #f))
+
 (define (environment->overlay-mount-maybe env)
   (let* ((name (symbol->string (environment-name env)))
          (dir (readlink (string-append "/tmp/genv/" name))))