bug#66339: [PATCH gnome-team v3] gnu: dbus-service: make the session available under /run/dbus

[Vivien Kraus via Bug reports for GNU Guix <bug-guix@gnu.org>]

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According to https://gitlab.gnome.org/GNOME/glib/-/merge_requests/3101, glib
now searches for the session bus socket in runstatedir. The dbus service must
thus have its socket in /run/dbus.

For interoperability with the dbus standard, /run/dbus is also symlinked to
/var/run/dbus.

* gnu/services/dbus.scm (dbus-activation): Symlink /run/dbus to /var/run/dbus.
(%dbus-accounts): Run dbus in /run/dbus.
(dbus-root-service-type): Save the pid file in /run/dbus.
---

Le jeudi 05 octobre 2023 à 06:41 +0200, Liliana Marie Prikler a écrit :
> > I’m still concerned about doing a symlink in the activation function.
> > What if we activate a new system from an existing one? Won’t the symlink
> > fail? I think we should preemptively delete /var/run/dbus and make a new
> > symlink every time. But I could be wrong, maybe this is not needed.
> >
> > What do you think?
> If we go this route, I think we should first check whether /var/run/dbus is
> indeed a symlink to /run/dbus and move the existing files if not before
> deleting the directory and creating the symlink.  But before that, we should
> try to symlink, which will fail with EEXIST if the file already exists,
> regardless of whether it's a symlink – thereafter you can check the cause of
> this failure through lstat.

I changed my mind! I now think it is OK for the system reconfigure to fail if
a different symlink already exists.

Best regards,

Vivien

 gnu/services/dbus.scm | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/gnu/services/dbus.scm b/gnu/services/dbus.scm
index 5a0c634393..206a7bb491 100644
--- a/gnu/services/dbus.scm
+++ b/gnu/services/dbus.scm
@@ -163,7 +163,7 @@ (define %dbus-accounts
          (group "messagebus")
          (system? #t)
          (comment "D-Bus system bus user")
-         (home-directory "/var/run/dbus")
+         (home-directory "/run/dbus")
          (shell (file-append shadow "/sbin/nologin")))))
 
 (define dbus-setuid-programs
@@ -186,7 +186,24 @@ (define (dbus-activation config)
         (let ((user (getpwnam "messagebus")))
           ;; This directory contains the daemon's socket so it must be
           ;; world-readable.
-          (mkdir-p/perms "/var/run/dbus" user #o755))
+          (mkdir-p/perms "/run/dbus" user #o755))
+
+        (catch 'system-error
+          (lambda ()
+            (symlink "/run/dbus" "/var/run/dbus"))
+          (lambda args
+            (let ((errno (system-error-errno args)))
+              (cond
+               ((= errno EEXIST)
+                (let ((existing-name
+                       (readlink "/run/dbus")))
+                  (unless (equal? existing-name "/var/run/dbus")
+                    (error "the symlink /run/dbus exists and does not point to /var/run/dbus"))))
+               (else
+                (format (current-error-port)
+                        "Failed to symlink /run/dbus to /var/run/dbus: ~s~%"
+                        (strerror errno))
+                (error "cannot create /var/run/dbus"))))))
 
         (unless (file-exists? "/etc/machine-id")
           (format #t "creating /etc/machine-id...~%")
@@ -210,7 +227,7 @@ (define dbus-shepherd-service
                              '(#:environment-variables '("DBUS_VERBOSE=1")
                                #:log-file "/var/log/dbus-daemon.log")
                              '())
-                      #:pid-file "/var/run/dbus/pid"))
+                      #:pid-file "/run/dbus/pid"))
             (stop #~(make-kill-destructor)))))))
 
 (define dbus-root-service-type

base-commit: b18b2d13488f2a92331ccad2dc8cbb54ee15582f
-- 
2.41.0