ui: 'with-profile-lock' keeps going upon ENOLCK.

* guix/build/syscalls.scm (call-with-file-lock/no-wait): Really pass
ARGS to HANDLER.  Return #f when HANDLER is called.
* guix/ui.scm (profile-lock-handler): Emit a mere warning upon ENOLCK.

guix/build/syscalls.scm

@@ -1127,7 +1127,9 @@ exception if it's already taken."
                 (lambda (key . args)
                   (match key
                     ('flock-error
-                     (handler args))
+                     (apply handler args)
+                     ;; No open port to the lock, so return #f.
+                     #f)
                     ('system-error
                       ;; When using the statically-linked Guile in the initrd,
                       ;; 'fcntl-flock' returns ENOSYS unconditionally.  Ignore

guix/ui.scm

@@ -1666,8 +1666,13 @@ DURATION-RELATION with the current time."
 
 (define (profile-lock-handler profile errno . _)
   "Handle failure to acquire PROFILE's lock."
-  (leave (G_ "profile ~a is locked by another process~%")
-         profile))
+  ;; NFS mounts can return ENOLCK.  When that happens, there's not much that
+  ;; can be done, so warn the user and keep going.
+  (if (= errno ENOLCK)
+      (warning (G_ "cannot lock profile ~a: ~a~%")
+               profile (strerror errno))
+      (leave (G_ "profile ~a is locked by another process~%")
+             profile)))
 
 (define profile-lock-file
   (cut string-append <> ".lock"))