--- /dev/null
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+
+#include <systemd/sd-bus.h>
+#define _cleanup_(f) __attribute__((cleanup(f)))
+
+/* This is equivalent to:
+ * busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 \
+ * org.freedesktop.systemd1.Manager GetUnitByPID $$
+ *
+ * Compile with 'cc -lsystemd print-unit-path.c'
+ */
+
+#define DESTINATION "org.freedesktop.systemd1"
+#define PATH "/org/freedesktop/systemd1"
+#define INTERFACE "org.freedesktop.systemd1.Manager"
+#define MEMBER "GetUnitByPID"
+
+static int log_error(int error, const char *message) {
+ fprintf(stderr, "%s: %s\n", message, strerror(-error));
+ return error;
+}
+
+static int print_unit_path(sd_bus *bus) {
+ _cleanup_(sd_bus_message_unrefp) sd_bus_message *m = NULL;
+ _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+ _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
+ int r;
+
+ r = sd_bus_message_new_method_call(bus, &m,
+ DESTINATION, PATH, INTERFACE, MEMBER);
+ if (r < 0)
+ return log_error(r, "Failed to create bus message");
+
+ r = sd_bus_message_append(m, "u", (unsigned) getpid());
+ if (r < 0)
+ return log_error(r, "Failed to append to bus message");
+
+ r = sd_bus_call(bus, m, -1, &error, &reply);
+ if (r < 0)
+ return log_error(r, "Call failed");
+
+ const char *ans;
+ r = sd_bus_message_read(reply, "o", &ans);
+ if (r < 0)
+ return log_error(r, "Failed to read reply");
+
+ printf("Unit path is \"%s\".\n", ans);
+
+ return 0;
+}
+
+int main(int argc, char **argv) {
+ _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+ int r;
+
+ r = sd_bus_open_system(&bus);
+ if (r < 0)
+ return log_error(r, "Failed to acquire bus");
+
+ print_unit_path(bus);
+}
--- /dev/null
+<?xml version='1.0'?>
+<!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_message_new_method_call"
+ xmlns:xi="http://www.w3.org/2001/XInclude">
+
+ <refentryinfo>
+ <title>sd_bus_message_new_method_call</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>sd_bus_message_new_method_call</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_bus_message_new_method_call</refname>
+
+ <refpurpose>Create a method call message</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int sd_bus_message_new_method_call</funcdef>
+ <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
+ <paramdef>sd_bus_message **<parameter>m</parameter></paramdef>
+ <paramdef>const char *<parameter>destination</parameter></paramdef>
+ <paramdef>const char *<parameter>path</parameter></paramdef>
+ <paramdef>const char *<parameter>interface</parameter></paramdef>
+ <paramdef>const char *<parameter>member</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>The <function>sd_bus_message_new_method_call()</function> function creates a new bus
+ message object that encapsulates a D-Bus method call, and returns it in the
+ <parameter>m</parameter> output parameter. The call will be made on the destination
+ <parameter>destination</parameter>, path <parameter>path</parameter>, on the interface
+ <parameter>interface</parameter>, member <parameter>member</parameter>.</para>
+
+ <para>Briefly, the <emphasis>destination</emphasis> is a dot-separated name that identifies a
+ service connected to the bus. The <emphasis>path</emphasis> is a slash-separated identifier of
+ an object within the destination that resembles a file system path. The meaning of this path is
+ defined by the destination. The <emphasis>interface</emphasis> is a dot-separated name that
+ resembles a Java interface name that identifies a group of methods and signals supported by the
+ object identified by path. Methods and signals are collectively called
+ <emphasis>members</emphasis> and are identified by a simple name composed of ASCII letters,
+ numbers, and underscores. See the <ulink
+ url="https://dbus.freedesktop.org/doc/dbus-tutorial.html#concepts">D-Bus Tutorial</ulink> for an
+ in-depth explanation.</para>
+
+ <para>The <parameter>destination</parameter> parameter may be <constant>NULL</constant>. The
+ <parameter>interface</parameter> parameter may be <constant>NULL</constant>, if the destination
+ has only a single member with the given name and there is no ambiguity if the interface name is
+ omitted.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para>This function returns 0 if the message object was successfully created, and a negative
+ errno-style error code otherwise.</para>
+ </refsect1>
+
+ <refsect1 id='errors'>
+ <title>Errors</title>
+
+ <para>Returned errors may indicate the following problems:</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><constant>-EINVAL</constant></term>
+
+ <listitem><para>The output parameter <parameter>m</parameter> is
+ <constant>NULL</constant>.</para>
+
+ <para>The <parameter>destination</parameter> parameter is non-null and is not a valid D-Bus
+ service name (<literal>org.somewhere.Something</literal>), the <parameter>path</parameter>
+ parameter is not a valid D-Bus path (<literal>/an/object/path</literal>), the
+ <parameter>interface</parameter> parameter is non-null and is not a valid D-Bus interface
+ name (<literal>an.interface.name</literal>), or the <parameter>member</parameter> parameter
+ is not a valid D-Bus member (<literal>Name</literal>).</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-ENOTCONN</constant></term>
+
+ <listitem><para>The bus parameter <parameter>bus</parameter> is <constant>NULL</constant> or
+ the bus is not connected.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-ENOMEM</constant></term>
+
+ <listitem><para>Memory allocation failed.</para></listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+ <xi:include href="libsystemd-pkgconfig.xml" />
+
+ <refsect1>
+ <title>Examples</title>
+
+ <example>
+ <title>Make a call to a D-Bus method that takes a single parameter</title>
+
+ <programlisting><xi:include href="print-unit-path.c" parse="text" /></programlisting>
+ <para>This defines a minimally useful program that will open a connection to the bus, create a
+ message object, send it, wait for the reply, and finally extract and print the answer. It does
+ error handling and proper memory management.</para>
+ </example>
+ </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_path_encode</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>
projects / thirdparty / systemd.git / commitdiff
