man: add sd_bus_message_new_call(3)
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
parent
e8b84fcca6
commit
cfe8ee463d
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@ -0,0 +1,64 @@
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#include <stdio.h>
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#include <string.h>
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#include <unistd.h>
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#include <sys/types.h>
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#include <systemd/sd-bus.h>
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#define _cleanup_(f) __attribute__((cleanup(f)))
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/* This is equivalent to:
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* busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 \
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* org.freedesktop.systemd1.Manager GetUnitByPID $$
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*
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* Compile with 'cc -lsystemd print-unit-path.c'
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*/
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#define DESTINATION "org.freedesktop.systemd1"
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#define PATH "/org/freedesktop/systemd1"
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#define INTERFACE "org.freedesktop.systemd1.Manager"
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#define MEMBER "GetUnitByPID"
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static int log_error(int error, const char *message) {
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fprintf(stderr, "%s: %s\n", message, strerror(-error));
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return error;
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}
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static int print_unit_path(sd_bus *bus) {
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_cleanup_(sd_bus_message_unrefp) sd_bus_message *m = NULL;
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_cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
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_cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
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int r;
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r = sd_bus_message_new_method_call(bus, &m,
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DESTINATION, PATH, INTERFACE, MEMBER);
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if (r < 0)
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return log_error(r, "Failed to create bus message");
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r = sd_bus_message_append(m, "u", (unsigned) getpid());
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if (r < 0)
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return log_error(r, "Failed to append to bus message");
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r = sd_bus_call(bus, m, -1, &error, &reply);
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if (r < 0)
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return log_error(r, "Call failed");
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const char *ans;
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r = sd_bus_message_read(reply, "o", &ans);
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if (r < 0)
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return log_error(r, "Failed to read reply");
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printf("Unit path is \"%s\".\n", ans);
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return 0;
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}
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int main(int argc, char **argv) {
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_cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
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int r;
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r = sd_bus_open_system(&bus);
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if (r < 0)
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return log_error(r, "Failed to acquire bus");
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print_unit_path(bus);
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}
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@ -210,6 +210,7 @@ manpages = [
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'3',
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['sd_bus_message_get_realtime_usec', 'sd_bus_message_get_seqnum'],
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''],
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['sd_bus_message_new_method_call', '3', [], ''],
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['sd_bus_message_new_method_error',
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'3',
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['sd_bus_message_new_method_errno',
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@ -60,6 +60,7 @@
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<citerefentry><refentrytitle>sd_bus_message_copy</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_get_cookie</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_new_method_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_new_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_read_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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@ -0,0 +1,134 @@
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<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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<refentry id="sd_bus_message_new_method_call"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_bus_message_new_method_call</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_bus_message_new_method_call</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_bus_message_new_method_call</refname>
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<refpurpose>Create a method call message</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int sd_bus_message_new_method_call</funcdef>
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<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
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<paramdef>sd_bus_message **<parameter>m</parameter></paramdef>
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<paramdef>const char *<parameter>destination</parameter></paramdef>
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<paramdef>const char *<parameter>path</parameter></paramdef>
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<paramdef>const char *<parameter>interface</parameter></paramdef>
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<paramdef>const char *<parameter>member</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>The <function>sd_bus_message_new_method_call()</function> function creates a new bus
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message object that encapsulates a D-Bus method call, and returns it in the
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<parameter>m</parameter> output parameter. The call will be made on the destination
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<parameter>destination</parameter>, path <parameter>path</parameter>, on the interface
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<parameter>interface</parameter>, member <parameter>member</parameter>.</para>
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<para>Briefly, the <emphasis>destination</emphasis> is a dot-separated name that identifies a
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service connected to the bus. The <emphasis>path</emphasis> is a slash-separated identifier of
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an object within the destination that resembles a file system path. The meaning of this path is
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defined by the destination. The <emphasis>interface</emphasis> is a dot-separated name that
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resembles a Java interface name that identifies a group of methods and signals supported by the
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object identified by path. Methods and signals are collectively called
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<emphasis>members</emphasis> and are identified by a simple name composed of ASCII letters,
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numbers, and underscores. See the <ulink
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url="https://dbus.freedesktop.org/doc/dbus-tutorial.html#concepts">D-Bus Tutorial</ulink> for an
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in-depth explanation.</para>
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<para>The <parameter>destination</parameter> parameter may be <constant>NULL</constant>. The
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<parameter>interface</parameter> parameter may be <constant>NULL</constant>, if the destination
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has only a single member with the given name and there is no ambiguity if the interface name is
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omitted.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>This function returns 0 if the message object was successfully created, and a negative
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errno-style error code otherwise.</para>
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</refsect1>
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<refsect1 id='errors'>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>The output parameter <parameter>m</parameter> is
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<constant>NULL</constant>.</para>
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<para>The <parameter>destination</parameter> parameter is non-null and is not a valid D-Bus
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service name (<literal>org.somewhere.Something</literal>), the <parameter>path</parameter>
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parameter is not a valid D-Bus path (<literal>/an/object/path</literal>), the
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<parameter>interface</parameter> parameter is non-null and is not a valid D-Bus interface
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name (<literal>an.interface.name</literal>), or the <parameter>member</parameter> parameter
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is not a valid D-Bus member (<literal>Name</literal>).</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOTCONN</constant></term>
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<listitem><para>The bus parameter <parameter>bus</parameter> is <constant>NULL</constant> or
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the bus is not connected.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Memory allocation failed.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>Examples</title>
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<example>
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<title>Make a call to a D-Bus method that takes a single parameter</title>
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<programlisting><xi:include href="print-unit-path.c" parse="text" /></programlisting>
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<para>This defines a minimally useful program that will open a connection to the bus, create a
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message object, send it, wait for the reply, and finally extract and print the answer. It does
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error handling and proper memory management.</para>
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</example>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_path_encode</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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@ -44,7 +44,11 @@
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object that encapsulates a D-Bus signal, and returns it in the <parameter>m</parameter> output
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parameter. The signal will be sent to path <parameter>path</parameter>, on the interface
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<parameter>interface</parameter>, member <parameter>member</parameter>. When this message is
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sent, no reply is expected.</para>
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sent, no reply is expected. See
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<citerefentry><refentrytitle>sd_bus_message_new_call</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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for a short description of the meaning of the <parameter>path</parameter>,
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<parameter>interface</parameter>, and <parameter>member</parameter> parameters.
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</para>
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</refsect1>
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<refsect1>
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@ -80,7 +80,7 @@
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always be <constant>NUL</constant>-terminated. The returned string
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will be the concatenation of the bus path prefix plus an escaped
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version of the external identifier string. This operation may be
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reversed with <function>sd_bus_decode()</function>. It is
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reversed with <function>sd_bus_path_decode()</function>. It is
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recommended to only use external identifiers that generally
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require little escaping to be turned into valid bus path
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identifiers (for example, by sticking to a 7-bit ASCII character
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