From 3fa1e930b827aebca2dbbfe84c36cf203f15afda Mon Sep 17 00:00:00 2001
From: Chris Marusich <address@hidden>
Date: Mon, 20 Aug 2018 00:16:06 -0700
Subject: [PATCH] gnu: services: Fix pcscd activation bug.

* gnu/services/security-token.scm (pcscd-activation): Idempotently create the
/var/lib/pcsc symlink so that it does not fail when it already exists.
---
 gnu/services/security-token.scm | 36 +++++++++++++++++++++++++--------
 1 file changed, 28 insertions(+), 8 deletions(-)

diff --git a/gnu/services/security-token.scm b/gnu/services/security-token.scm
index 7e7ea54a5..8bea49538 100644
--- a/gnu/services/security-token.scm
+++ b/gnu/services/security-token.scm
@@ -20,6 +20,7 @@
   #:use-module (gnu services)
   #:use-module (gnu services shepherd)
   #:use-module (gnu packages admin)
+  #:use-module (gnu packages base)
   #:use-module (gnu packages security-token)
   #:use-module (gnu system shadow)
   #:use-module (guix gexp)
@@ -62,14 +63,33 @@
 (define pcscd-activation
   (match-lambda
     (($ <pcscd-configuration> pcsc-lite usb-drivers)
-     #~(begin
-         (use-modules (guix build utils))
-         (mkdir-p "/var/lib")
-         (symlink #$(directory-union
-                     "pcsc"
-                     (map (cut file-append <> "/pcsc")
-                          usb-drivers))
-                  "/var/lib/pcsc")))))
+     (with-imported-modules (source-module-closure
+                             '((guix build utils)))
+       #~(begin
+           (use-modules (guix build utils))
+           ;; This switch-symlinks procedure was copied from (guix utils).  It
+           ;; would be nice to re-use the procedure from that module, but if
+           ;; we add that module to this gexp's imported modules and try to
+           ;; use it, then this activation gexp can fail when it runs.  To be
+           ;; specific, if you try to use (guix utils) and then build a VM
+           ;; with a pcscd-service-type using "guix system vm-image", then
+           ;; when you boot the VM, it will fail.  It fails because (guix
+           ;; utils) dynamically links glibc's strverscmp function when
+           ;; defining the version-compare procedure, and for some reason
+           ;; strverscmp can't be found.  Perhaps there's a way to fix or
+           ;; avoid this, but since we don't need the version-compare
+           ;; procedure here, anyway, it's simpler to just define our own
+           ;; switch-symlinks procedure instead.
+           (define (switch-symlinks link target)
+             (let ((pivot (string-append link ".new")))
+               (symlink target pivot)
+               (rename-file pivot link)))
+           (mkdir-p "/var/lib")
+           (switch-symlinks "/var/lib/pcsc"
+                            #$(directory-union
+                               "pcsc"
+                               (map (cut file-append <> "/pcsc")
+                                    usb-drivers))))))))
 
 (define pcscd-service-type
   (service-type
-- 
2.18.0