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Merge pull request #9132 from poettering/sd-bus-slot-set-floating

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make sure we don't leak bus slots when sd_bus_add_match_async() is used
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Lennart Poettering 2018-05-31 00:58:41 +02:00 committed by GitHub
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9 changed files with 205 additions and 22 deletions
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1
man/rules/meson.build
View File

@ -231,6 +231,7 @@ manpages = [
['sd_bus_set_connected_signal', '3', ['sd_bus_get_connected_signal'], ''],
['sd_bus_set_sender', '3', ['sd_bus_get_sender'], ''],
['sd_bus_set_watch_bind', '3', ['sd_bus_get_watch_bind'], ''],
['sd_bus_slot_set_floating', '3', ['sd_bus_slot_get_floating'], ''],
['sd_bus_track_add_name',
'3',
['sd_bus_track_add_sender',

9
man/sd_bus_add_match.xml
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@ -123,7 +123,7 @@
name), from which the match string is internally generated. Optionally, these parameters may be specified as
<constant>NULL</constant> in which case the relevant field of incoming signals is not tested.</para>
<para><function>sd_bus_match_signal_async()</function> is combines the signal matching logic of
<para><function>sd_bus_match_signal_async()</function> combines the signal matching logic of
<function>sd_bus_match_signal()</function> with the asynchronous behaviour of
<function>sd_bus_add_match_async()</function>.</para>
@ -132,7 +132,9 @@
at a later time with
<citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If specified
as <constant>NULL</constant> the lifetime of the match is bound to the lifetime of the bus object itself, and the
match cannot be removed independently.</para>
match is generally not removed independently. See
<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
details.</para>
<para>The message <parameter>m</parameter> passed to the callback is only borrowed, that is, the callback should
not call <citerefentry><refentrytitle>sd_bus_message_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
@ -175,7 +177,8 @@
<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_set_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>
<citerefentry><refentrytitle>sd_bus_set_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>

35
man/sd_bus_default.xml
View File

@ -206,21 +206,26 @@
<citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
to drop the reference.</para>
<para>Queued but unwritten/unread messages also keep a reference
to their bus connection object. For this reason, even if an
application dropped all references to a bus connection, it might
not get destroyed right away. Until all incoming queued
messages are read, and until all outgoing unwritten messages are
written, the bus object will stay
alive. <function>sd_bus_flush()</function> may be used to write
all outgoing queued messages so they drop their references. To
flush the unread incoming messages, use
<function>sd_bus_close()</function>, which will also close the bus
connection. When using the default bus logic, it is a good idea to
first invoke <function>sd_bus_flush()</function> followed by
<function>sd_bus_close()</function> when a thread or process
terminates, and thus its bus connection object should be
freed.</para>
<para>Queued but unwritten/unread messages keep a reference to their bus connection object. For this reason, even
if an application dropped all references to a bus connection, it might not get destroyed right away. Until all
incoming queued messages are read, and until all outgoing unwritten messages are written, the bus object will stay
alive. <function>sd_bus_flush()</function> may be used to write all outgoing queued messages so they drop their
references. To flush the unread incoming messages, use <function>sd_bus_close()</function>, which will also close
the bus connection. When using the default bus logic, it is a good idea to first invoke
<function>sd_bus_flush()</function> followed by <function>sd_bus_close()</function> when a thread or process
terminates, and thus its bus connection object should be freed.</para>
<para>Normally, slot objects (as created by
<citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> and similar
calls) keep a reference to their bus connection object, too. Thus, as long as a bus slot object remains referenced
its bus object will remain allocated too. Optionally, bus slot objects may be placed in "floating" mode. When in
floating mode the life cycle of the bus slot object is bound to the bus object, i.e. when the bus object is freed
the bus slot object is automatically unreferenced too. The floating state of a slot object may be controlled
explicitly with
<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
though usually floating bus slot objects are created by passing <constant>NULL</constant> as the
<parameter>slot</parameter> parameter of <function>sd_bus_add_match()</function> and related calls, thus indicating
that the caller is not directly interested in referencing and managing the bus slot object.</para>
<para>The life cycle of the default bus connection should be the
responsibility of the code that creates/owns the thread the

118
man/sd_bus_slot_set_floating.xml Normal file
View File

@ -0,0 +1,118 @@
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<refentry id="sd_bus_slot_set_floating">
<refentryinfo>
<title>sd_bus_slot_set_floating</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_bus_slot_set_floating</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_slot_set_floating</refname>
<refname>sd_bus_slot_get_floating</refname>
<refpurpose>Control whether a bus slot object is "floating".</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_bus_slot_set_floating</function></funcdef>
<paramdef>sd_bus_slot *<parameter>bus</parameter></paramdef>
<paramdef>int <parameter>b</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_slot_get_floating</function></funcdef>
<paramdef>sd_bus_slot *<parameter>slot</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_bus_slot_set_floating()</function> controls whether the specified bus slot object
<parameter>slot</parameter> shall be "floating" or not. A floating bus slot object's lifetime is bound to the
lifetime of the bus object it is associated with, meaning that it remains allocated as long as the bus object
itself and is freed automatically when the bus object is freed. Regular (i.e. non-floating) bus slot objects keep
the bus referenced, hence the bus object remains allocated at least as long as there remains at least one
referenced bus slot object around. The floating state hence controls the direction of referencing between the bus
object and the bus slot objects: if floating the bus pins the the bus slot, and otherwise the bus slot pins the bus
objects. Use <function>sd_bus_slot_set_floating()</function> to switch between both modes: if the
<parameter>b</parameter> parameter is zero, the slot object is considered floating, otherwise it is made a regular
(non-floating) slot object.</para>
<para>Bus slot objects may be allocated with calls such as
<citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If the
<parameter>slot</parameter> of these functions is non-<constant>NULL</constant> the slot object will be of the
regular kind (i.e. non-floating), otherwise it will be created floating. With
<function>sd_bus_slot_set_floating()</function> a bus slot object allocated as regular can be converted into a
floating object and back. This is particularly useful for creating a bus slot object, then changing parameters of
it, and then turning it into a floating object, whose lifecycle is managed by the bus object.</para>
<para><function>sd_bus_slot_get_floating()</function> returns the current floating state of the specified bus slot
object. It returns negative on error, zero if the bus slot object is a regular (non-floating) object and positive
otherwise.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style
error code.</para>
</refsect1>
<refsect1>
<title>Errors</title>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><constant>-ECHILD</constant></term>
<listitem><para>The bus connection has been created in a different process.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ESTALE</constant></term>
<listitem><para>The bus object the specified bus slot object is associated with has already been freed, and
hence no change in the floating state can be made anymore.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Notes</title>
<para><function>sd_bus_slot_set_floating()</function> and <function>sd_bus_slot_get_floating()</function> are
available as a shared library, which can be compiled and linked to with the
<constant>libsystemd</constant> <citerefentry
project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>

2
src/libsystemd/libsystemd.sym
View File

@ -561,4 +561,6 @@ global:
sd_bus_open_with_description;
sd_bus_open_user_with_description;
sd_bus_open_system_with_description;
sd_bus_slot_get_floating;
sd_bus_slot_set_floating;
} LIBSYSTEMD_238;

8
src/libsystemd/sd-bus/bus-internal.h
View File

@ -128,7 +128,15 @@ struct sd_bus_slot {
sd_bus *bus;
void *userdata;
BusSlotType type:5;
/* Slots can be "floating" or not. If they are not floating (the usual case) then they reference the bus object
* they are associated with. This means the bus object stays allocated at least as long as there is a slot
* around associated with it. If it is floating, then the slot's lifecycle is bound to the lifecycle of the
* bus: it will be disconnected from the bus when the bus is destroyed, and it keeping the slot reffed hence
* won't mean the bus stays reffed too. Internally this means the reference direction is reversed: floating
* slots objects are referenced by the bus object, and not vice versa. */
bool floating:1;
bool match_added:1;
char *description;

40
src/libsystemd/sd-bus/bus-slot.c
View File

@ -260,6 +260,37 @@ _public_ void* sd_bus_slot_get_current_userdata(sd_bus_slot *slot) {
return slot->bus->current_userdata;
}
_public_ int sd_bus_slot_get_floating(sd_bus_slot *slot) {
assert_return(slot, -EINVAL);
return slot->floating;
}
_public_ int sd_bus_slot_set_floating(sd_bus_slot *slot, int b) {
assert_return(slot, -EINVAL);
if (slot->floating == !!b)
return 0;
if (!slot->bus) /* already disconnected slots can't be reconnected */
return -ESTALE;
slot->floating = b;
/* When a slot is "floating" then the bus references the slot. Otherwise the slot references the bus. Hence,
* when we move from one to the other, let's increase one reference and decrease the other. */
if (b) {
sd_bus_slot_ref(slot);
sd_bus_unref(slot->bus);
} else {
sd_bus_ref(slot->bus);
sd_bus_slot_unref(slot);
}
return 1;
}
_public_ int sd_bus_slot_set_description(sd_bus_slot *slot, const char *description) {
assert_return(slot, -EINVAL);
@ -269,8 +300,13 @@ _public_ int sd_bus_slot_set_description(sd_bus_slot *slot, const char *descript
_public_ int sd_bus_slot_get_description(sd_bus_slot *slot, const char **description) {
assert_return(slot, -EINVAL);
assert_return(description, -EINVAL);
assert_return(slot->description, -ENXIO);
*description = slot->description;
if (slot->description)
*description = slot->description;
else if (slot->type == BUS_MATCH_CALLBACK)
*description = slot->match_callback.match_string;
else
return -ENXIO;
return 0;
}

12
src/libsystemd/sd-bus/sd-bus.c
View File

@ -3227,13 +3227,21 @@ static int bus_add_match_full(
goto finish;
}
if (asynchronous)
if (asynchronous) {
r = bus_add_match_internal_async(bus,
&s->match_callback.install_slot,
s->match_callback.match_string,
add_match_callback,
s);
else
if (r < 0)
return r;
/* Make the slot of the match call floating now. We need the reference, but we don't
* want that this match pins the bus object, hence we first create it non-floating, but
* then make it floating. */
r = sd_bus_slot_set_floating(s->match_callback.install_slot, true);
} else
r = bus_add_match_internal(bus, s->match_callback.match_string);
if (r < 0)
goto finish;

2
src/systemd/sd-bus.h
View File

@ -228,6 +228,8 @@ void *sd_bus_slot_get_userdata(sd_bus_slot *slot);
void *sd_bus_slot_set_userdata(sd_bus_slot *slot, void *userdata);
int sd_bus_slot_set_description(sd_bus_slot *slot, const char *description);
int sd_bus_slot_get_description(sd_bus_slot *slot, const char **description);
int sd_bus_slot_get_floating(sd_bus_slot *slot);
int sd_bus_slot_set_floating(sd_bus_slot *slot, int b);
sd_bus_message* sd_bus_slot_get_current_message(sd_bus_slot *slot);
sd_bus_message_handler_t sd_bus_slot_get_current_handler(sd_bus_slot *bus);