From b391ab0fb9d45c1ef00bd12f25d240801db62cbf Mon Sep 17 00:00:00 2001
From: Simon McVittie <simon.mcvittie@collabora.co.uk>
Date: Mon, 18 Feb 2013 18:20:00 +0000
Subject: [PATCH 3/5] sd_uid_get_display: add

This can be used to get a best-effort X11 display, suitable for passing
to user-bus-activated services.

Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
---
 Makefile.am                    |    1 +
 man/sd_uid_get_state.xml       |   22 ++++++++++++++++++++++
 src/login/libsystemd-login.sym |    1 +
 src/login/sd-login.c           |   26 ++++++++++++++++++++++++++
 src/systemd/sd-login.h         |    3 +++
 5 files changed, 53 insertions(+)

diff --git a/Makefile.am b/Makefile.am
index 10934eb..62a91aa 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -896,6 +896,7 @@ libsystemd_core_la_LIBADD = \
 	libsystemd-audit.la \
 	libsystemd-id128-internal.la \
 	libsystemd-daemon.la \
+	libsystemd-login-internal.la \
 	libudev.la \
 	$(LIBWRAP_LIBS) \
 	$(PAM_LIBS) \
diff --git a/man/sd_uid_get_state.xml b/man/sd_uid_get_state.xml
index cc8fc0f..6cfc6b7 100644
--- a/man/sd_uid_get_state.xml
+++ b/man/sd_uid_get_state.xml
@@ -47,6 +47,7 @@
                 <refname>sd_uid_is_on_seat</refname>
                 <refname>sd_uid_get_sessions</refname>
                 <refname>sd_uid_get_seats</refname>
+                <refname>sd_uid_get_display</refname>
                 <refpurpose>Determine login state of a specific Unix user ID</refpurpose>
         </refnamediv>
 
@@ -80,6 +81,12 @@
                                 <paramdef>int <parameter>require_active</parameter></paramdef>
                                 <paramdef>char*** <parameter>seats</parameter></paramdef>
                         </funcprototype>
+
+                        <funcprototype>
+                                <funcdef>int <function>sd_uid_get_display</function></funcdef>
+                                <paramdef>uid_t <parameter>uid</parameter></paramdef>
+                                <paramdef>char** <parameter>display</parameter></paramdef>
+                        </funcprototype>
                 </funcsynopsis>
         </refsynopsisdiv>
 
@@ -147,6 +154,15 @@
                 with no attached seat and hence the number of entries
                 in the returned array may differ from the one returned
                 by <function>sd_uid_get_sessions()</function>.</para>
+
+                <para><function>sd_uid_get_display()</function> may
+                be used to determine an X11 display for the
+                specified user. If they have more than one, an arbitrary one
+                is returned. The display returned through the
+                <parameter>display</parameter> needs to be
+                freed by the caller with the libc
+                <citerefentry><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                function.</para>
         </refsect1>
 
         <refsect1>
@@ -162,6 +178,11 @@
                 number of entries in the returned arrays. On failure,
                 these calls return a negative errno-style error
                 code.</para>
+
+                <para>On success,
+                <function>sd_uid_get_display()</function>
+                returns 0. On failure, it returns a negative errno-style
+                error code.</para>
         </refsect1>
 
         <refsect1>
@@ -169,6 +190,7 @@
 
                 <para>The <function>sd_uid_get_state()</function>,
                 <function>sd_uid_is_on_seat()</function>,
+                <function>sd_uid_get_display()</function>,
                 <function>sd_uid_get_sessions()</function>, and
                 <function>sd_uid_get_seats()</function> interfaces are
                 available as shared library, which can be compiled and
diff --git a/src/login/libsystemd-login.sym b/src/login/libsystemd-login.sym
index 272b0e2..7a53332 100644
--- a/src/login/libsystemd-login.sym
+++ b/src/login/libsystemd-login.sym
@@ -57,4 +57,5 @@ global:
 LIBSYSTEMD_LOGIN_198 {
 global:
         sd_session_get_tty;
+        sd_uid_get_display;
 } LIBSYSTEMD_LOGIN_186;
diff --git a/src/login/sd-login.c b/src/login/sd-login.c
index 8867e8c..2214a87 100644
--- a/src/login/sd-login.c
+++ b/src/login/sd-login.c
@@ -165,6 +165,32 @@ _public_ int sd_uid_get_state(uid_t uid, char**state) {
         return 0;
 }
 
+_public_ int sd_uid_get_display(uid_t uid, char **display) {
+        char *p, *s = NULL;
+        int r;
+
+        if (!display)
+                return -EINVAL;
+
+        if (asprintf(&p, "/run/systemd/users/%lu", (unsigned long) uid) < 0)
+                return -ENOMEM;
+
+        r = parse_env_file(p, NEWLINE, "DISPLAY", &s, NULL);
+        free(p);
+
+        if (r < 0) {
+                free(s);
+                return r;
+        } else if (isempty(s)) {
+                free(s);
+                return -ENOENT;
+        }
+
+        r = sd_session_get_display(s, display);
+        free(s);
+        return r;
+}
+
 _public_ int sd_uid_is_on_seat(uid_t uid, int require_active, const char *seat) {
         char *p, *w, *t, *state, *s = NULL;
         size_t l;
diff --git a/src/systemd/sd-login.h b/src/systemd/sd-login.h
index 3746b45..dcc8ab3 100644
--- a/src/systemd/sd-login.h
+++ b/src/systemd/sd-login.h
@@ -82,6 +82,9 @@ int sd_uid_get_sessions(uid_t uid, int require_active, char ***sessions);
  * just return number of seats.*/
 int sd_uid_get_seats(uid_t uid, int require_active, char ***seats);
 
+/* If uid has a session with an X11 display, get it. */
+int sd_uid_get_display(uid_t uid, char **display);
+
 /* Return 1 if the session is a active. */
 int sd_session_is_active(const char *session);
 
-- 
1.7.10.4