DBus services

The message bus can start applications (services) on behalf of other applications, the application asks DBus to start a service by its name, usually the name should be known such as org.freedesktop.TextEditor.

In order for DBus to find the executable corresponding to a particular name, the bus daemon looks for service description files which usually are installed in /usr/share/dbus-1/services and they have .service in their extension name (all linux distros that i know they use this prefix to install dbus services files), as an example of a service file.

DBus service file example:

[D-BUS Service]

Name=org.share.linux

Exec=path to the executable.

We will write two programs, one is the service that we want to start the other is the application that activates this service

share-linux-serivce-example.c

#include <stdio.h>

#include <dbus/dbus.h>

int main()

{

DBusConnection *connection;

DBusError error;

 

dbus_error_init(&error);

connection = dbus_bus_get(DBUS_BUS_STARTER, &error); /* DBUS_BUS_STARTER is

the bus that started us */

/* Do something here to make sure that the application was successfully

started by DBus

* Example could be something like

* FILE *tmp;

* tmp = fopen("/tmp/share-linux-service.result", "w");

* fprintf(tmp,"share-linux service was started successfully");

* fclose(tmp);

* /

 

/* After that you have the service up, so you can do whetever you like */

dbus_connection_unref(connection);

 

return 0;

}

Compile this example with dbus-1 argument for pkg-config, you need to install the service file in /usr/share/dbus-1/service, name it org.share.linux and edit the

Exec path to where you have the service example binary.

start-service.c

#include <stdio.h>

#include <dbus/dbus.h>int main()

{

DBusConnection *connection;

DBusError error;

DBusMessage *message;

 

const char *service_name = "org.share.linux";

dbus_uint32_t flag; /* Currently this is not used by DBus, they say it is for

futur expansion*/

dbus_bool_t result;

 

dbus_error_init(&error);

 

connection = dbus_bus_get(DBUS_BUS_SESSION, &error);

 

if ( dbus_error_is_set(&error) )

{

printf("Error getting dbus connection: %s\n",error.message);

dbus_error_free(&error);

dbus_connection_unref(connection);

return 0;

}

 

message = dbus_message_new_method_call("org.freedesktop.DBus",

"/org/freedesktop/DBus",

"org.freedesktop.DBus",

"StartServiceByName");

 

if ( !message )

{

printf("Error creating DBus message\n");

dbus_connection_unref(connection);

return 0;

}

 

dbus_message_set_no_reply(message, TRUE); /* We don't want to receive a reply

*/

 

/* Append the argument to the message, must ends with DBUS_TYPE_UINT32 */

dbus_message_append_args(message,

DBUS_TYPE_STRING,

&service_name,

DBUS_TYPE_UINT32,

&flag,

DBUS_TYPE_INVALID);

 

result = dbus_connection_send(connection, message, NULL);

 

 

if ( result == TRUE )

{

printf("Successfully activating the %s service\n",service_name);

}

else

{

printf("Failed to activate the %s service\n",service_name);

}

dbus_message_unref(message);

dbus_connection_unref(connection);

return 0;

}

http://linoxide.com/how-tos/d-bus-ipc-mechanism-linux/