D-BUS unable to receive few signals.

[abhijeet.sinha1 at wipro.com]

Hello,

I was trying to trigger some task when DHCP does an DHCPACK on an IP. This I thought of achieving by using dbus signals.

I picked up the code from the following page -- http://dbus.freedesktop.org/doc/dbus/libdbus-tutorial.html <http://dbus.freedesktop.org/doc/dbus/libdbus-tutorial.html>  Read the "Receiving a Signal" section and modified it to my own requirements.

As for sending the signal I used the dbus-send command from DHCP server ( Inserting few statements in ISC DHCP's dhcpd.conf file by which on commit or on release the dbus-send command in triggered )
I am facing a problem, where some Signals do not reach the dbus server program. It happens once in 40-50 signals. But my application would not want to lose the Signals.

Part of my Code
dbus-server.c

#include <dbus/dbus.h>
#include <stdbool.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include<string.h>
void receive()
{
   DBusMessage* msg;
   DBusMessageIter args;
   DBusConnection* conn;
   DBusError err;
   int ret, ipcheck;
   char *sigvalue1, *message;
   dbus_bool_t sigvalue2;
   bool request_type;
   static int sequence_number = 0;
   dbus_error_init(&err);
   conn = dbus_bus_get(DBUS_BUS_SYSTEM, &err);
   ret = dbus_bus_request_name(conn, "com.example.app.Sink",  DBUS_NAME_FLAG_REPLACE_EXISTING , &err);
   dbus_bus_add_match(conn, "type='signal',interface='com.example.app.Signal'", &err);
   dbus_connection_flush(conn);
   // All the checks were made to see if the connection is established. 
   while (true)
   {
       dbus_connection_read_write(conn, 0);
       msg = dbus_connection_pop_message(conn);
       if (NULL == msg) {
           sleep(1);
           continue;
       }
       if (dbus_message_is_signal(msg, "com.example.app.Signal", "Test"))
       {
           fprintf(stdout,"\n#####################################################\n");
           sequence_number++;
           fprintf(stdout,"\nSignal Sequence Number: %d\n",sequence_number);
           fflush(stdout);
           if (dbus_message_iter_init(msg, &args))
           {
                dbus_message_iter_get_basic(&args,&sigvalue1);
                dbus_message_iter_next(&args);
                dbus_message_iter_get_basic(&args,&sigvalue2);
                fflush(stdout);
                if( sigvalue2 )
                    request_type=true;
                else
                    request_type=false;
                if ( request_type )
                {
                    // DO SOMETHING
                    dbus_message_unref(msg);
                    continue;
                }
                else
                {
                    // DO SOMETHING ELSE
                    dbus_message_unref(msg);
                    continue;
                }
           }
       }
       dbus_message_unref(msg);
    } // end of while loop
 }



A dbus-send command is sent using --

dbus-send --system --dest='com.example.app.Sink' --type=signal /com/example/app/Signal com.example.app.Signal.Test string:"192.168.47.100" boolean:true
or

dbus-send --system --dest='com.example.app.Sink' --type=signal /com/example/app/Signal com.example.app.Signal.Test string:"192.168.47.100" boolean:false


I have an xml conf file in /etc/dbus-1/system.d/app.conf

<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd <http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd> ">
<busconfig>
    <policy user="root">
            <allow own="com.example.app.Source"/>
            <allow send_interface="com.example.app.Signal"/>
            <allow send_destination="com.example.app.Sink"/>
    </policy>
    <policy user="root">
            <allow own="com.example.app.Sink"/>
    </policy>
    <policy context="default">
            <deny own="com.example.app.Source"/>
            <deny send_destination="com.example.app.Sink"/>
            <deny send_interface="com.example.app.Signal"/>
    </policy>
</busconfig>



I modified the dbus-server.c code to change the following

dbus_connection_read_write(conn, 0); to 

dbus_connection_read_write(conn, 1); and 

dbus_connection_read_write(conn, 2);

But none had the required effect. Is there any glitch which is left which makes it lose the Signal ? I have picked most part of the code from the example provided on the tutorial, so I assume it should work. Please provide any leads as to what is making the Signal to be lost.

Regards,

Abhijeet Kumar Sinha
Project Engineer
Wipro Technologies
Bangalore






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