sd-bus: also add destroy callbacks to sd_bus_track objects

This augments previous work for this for sd_bus_slot objects, and adds
the same concept to sd_bus_track objects, too.

man/rules/meson.build

@@ -233,7 +233,10 @@ manpages = [
  ['sd_bus_set_watch_bind', '3', ['sd_bus_get_watch_bind'], ''],
  ['sd_bus_slot_set_destroy_callback',
   '3',
-  ['sd_bus_slot_get_destroy_callback'],
+  ['sd_bus_destroy_t',
+   'sd_bus_slot_get_destroy_callback',
+   'sd_bus_track_get_destroy_callback',
+   'sd_bus_track_set_destroy_callback'],
   ''],
  ['sd_bus_slot_set_floating', '3', ['sd_bus_slot_get_floating'], ''],
  ['sd_bus_track_add_name',

man/sd_bus_slot_set_destroy_callback.xml

@@ -20,6 +20,9 @@
   <refnamediv>
     <refname>sd_bus_slot_set_destroy_callback</refname>
     <refname>sd_bus_slot_get_destroy_callback</refname>
+    <refname>sd_bus_track_set_destroy_callback</refname>
+    <refname>sd_bus_track_get_destroy_callback</refname>
+    <refname>sd_bus_destroy_t</refname>
 
     <refpurpose>Define the callback function for resource cleanup.</refpurpose>
   </refnamediv>
@@ -44,35 +47,54 @@
         <paramdef>sd_bus_slot *<parameter>slot</parameter></paramdef>
         <paramdef>sd_bus_destroy_t *<parameter>callback</parameter></paramdef>
       </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_track_set_destroy_callback</function></funcdef>
+        <paramdef>sd_bus_track *<parameter>track</parameter></paramdef>
+        <paramdef>sd_bus_destroy_t <parameter>callback</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_track_get_destroy_callback</function></funcdef>
+        <paramdef>sd_bus_track *<parameter>track</parameter></paramdef>
+        <paramdef>sd_bus_destroy_t *<parameter>callback</parameter></paramdef>
+      </funcprototype>
     </funcsynopsis>
   </refsynopsisdiv>
 
   <refsect1>
     <title>Description</title>
 
-    <para><function>sd_bus_slot_set_destroy_callback()</function> sets
+    <para><function>sd_bus_slot_set_destroy_callback()</function> sets <parameter>callback</parameter> as the callback
-    <parameter>callback</parameter> as the callback function to be called right before the bus slot
+    function to be called right before the bus slot object <parameter>slot</parameter> is deallocated. The
-    object <parameter>slot</parameter> is deallocated. The <parameter>userdata</parameter> pointer
+    <parameter>userdata</parameter> pointer from the slot object will be passed as the <parameter>userdata</parameter>
-    from the slot object will be passed as the <parameter>userdata</parameter> parameter. This
+    parameter. This pointer can be set by an argument to the constructor functions, see
-    pointer can be set specified as an argument to the constuctor functions, see
+    <citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>, or directly,
-    <citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+    see <citerefentry><refentrytitle>sd_bus_slot_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
-    or directly, see
+    This callback function is called even if <parameter>userdata</parameter> is <constant>NULL</constant>. Note that
-    <citerefentry><refentrytitle>sd_bus_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
+    this callback is invoked at a time where the bus slot object itself is already invalidated, and executing
-    This callback function is called even if <parameter>userdata</parameter> is
+    operations or taking new references to the bus slot object is not permissible.</para>
-    <constant>NULL</constant>.</para>
 
     <para><function>sd_bus_slot_get_destroy_callback()</function> returns the current callback
     for <parameter>slot</parameter> in the <parameter>callback</parameter> parameter.</para>
+
+    <para><function>sd_bus_track_set_destroy_callback()</function> and
+    <function>sd_bus_track_get_destroy_callback</function> provide equivalent functionality for the
+    <parameter>userdata</parameter> pointer associated with bus peer tracking objects. For details about bus peer
+    tracking objects, see
+    <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
   </refsect1>
 
   <refsect1>
     <title>Return Value</title>
 
-    <para>On success, <function>sd_bus_slot_set_destroy_callback()</function> returns 0 or a
+    <para>On success, <function>sd_bus_slot_set_destroy_callback()</function> and
-    positive integer. On failure, it returns a negative errno-style error code.</para>
+    <function>sd_bus_track_set_destroy_callback()</function> return 0 or a positive integer. On failure, they return a
+    negative errno-style error code.</para>
 
-    <para><function>sd_bus_slot_get_destroy_callback()</function> returns 1 if the destroy callback
+    <para><function>sd_bus_slot_get_destroy_callback()</function> and
-    function is set, 0 if not. On failure, it returns a negative errno-style error code.</para>
+    <function>sd_bus_track_get_destroy_callback</function> return positive if the destroy callback function is set, 0
+    if not. On failure, they return a negative errno-style error code.</para>
   </refsect1>
 
   <refsect1>
@@ -84,8 +106,8 @@
       <varlistentry>
         <term><constant>-EINVAL</constant></term>
 
-        <listitem><para>The <parameter>slot</parameter> parameter is <constant>NULL</constant>.
+        <listitem><para>The <parameter>slot</parameter> or <parameter>track</parameter> parameter is
-        </para></listitem>
+        <constant>NULL</constant>.</para></listitem>
       </varlistentry>
     </variablelist>
   </refsect1>
@@ -98,7 +120,11 @@
     <para>
       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
-      <citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+      <citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_bus_slot_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_bus_track_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>
     </para>
   </refsect1>
 

src/libsystemd/libsystemd.sym

@@ -565,6 +565,8 @@ global:
         sd_bus_slot_set_floating;
         sd_bus_slot_get_destroy_callback;
         sd_bus_slot_set_destroy_callback;
+        sd_bus_track_get_destroy_callback;
+        sd_bus_track_set_destroy_callback;
         sd_event_add_inotify;
         sd_event_source_get_inotify_mask;
 } LIBSYSTEMD_238;

src/libsystemd/sd-bus/bus-track.c

@@ -31,6 +31,7 @@ struct sd_bus_track {
         bool in_queue:1;   /* In bus->track_queue? */
         bool modified:1;
         bool recursive:1;
+        sd_bus_destroy_t destroy_callback;
 
         LIST_FIELDS(sd_bus_track, tracks);
 };
@@ -164,18 +165,21 @@ _public_ sd_bus_track* sd_bus_track_unref(sd_bus_track *track) {
                 return NULL;
 
         assert(track->n_ref > 0);
+        track->n_ref--;
 
-        if (track->n_ref > 1) {
+        if (track->n_ref > 0)
-                track->n_ref--;
                 return NULL;
-        }
 
         if (track->in_list)
                 LIST_REMOVE(tracks, track->bus->tracks, track);
 
         bus_track_remove_from_queue(track);
-        hashmap_free_with_destructor(track->names, track_item_free);
+        track->names = hashmap_free_with_destructor(track->names, track_item_free);
-        sd_bus_unref(track->bus);
+        track->bus = sd_bus_unref(track->bus);
+
+        if (track->destroy_callback)
+                track->destroy_callback(track->userdata);
+
         return mfree(track);
 }
 
@@ -439,6 +443,22 @@ _public_ void *sd_bus_track_set_userdata(sd_bus_track *track, void *userdata) {
         return ret;
 }
 
+_public_ int sd_bus_track_set_destroy_callback(sd_bus_track *track, sd_bus_destroy_t callback) {
+        assert_return(track, -EINVAL);
+
+        track->destroy_callback = callback;
+        return 0;
+}
+
+_public_ int sd_bus_track_get_destroy_callback(sd_bus_track *track, sd_bus_destroy_t *ret) {
+        assert_return(track, -EINVAL);
+
+        if (ret)
+                *ret = track->destroy_callback;
+
+        return !!track->destroy_callback;
+}
+
 _public_ int sd_bus_track_set_recursive(sd_bus_track *track, int b) {
         assert_return(track, -EINVAL);
 

src/systemd/sd-bus.h

@@ -485,6 +485,9 @@ const char* sd_bus_track_contains(sd_bus_track *track, const char *name);
 const char* sd_bus_track_first(sd_bus_track *track);
 const char* sd_bus_track_next(sd_bus_track *track);
 
+int sd_bus_track_set_destroy_callback(sd_bus_track *s, sd_bus_destroy_t callback);
+int sd_bus_track_get_destroy_callback(sd_bus_track *s, sd_bus_destroy_t *ret);
+
 /* Define helpers so that __attribute__((cleanup(sd_bus_unrefp))) and similar may be used. */
 _SD_DEFINE_POINTER_CLEANUP_FUNC(sd_bus, sd_bus_unref);
 _SD_DEFINE_POINTER_CLEANUP_FUNC(sd_bus, sd_bus_flush_close_unref);