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       smokeping_extend - Notes on extending Smokeping


       This document is intended to guide prospective authors in writing new
       Smokeping probes.  It mostly describes the interface between Smokeping
       and its probe modules. If it seems too complicated to understand, look
       at the existing modules for examples.

       Comments and proposed changes or additions are welcome.  Please send
       them to the smokeping-users mailing list. Patches against the POD
       source of this document are most appreciated.


       The first thing you should decide is which base class you should use
       for your probe. For most (if not all) uses it’s a choice between
       Smokeping::probes::base and Smokeping::probes::basefork. The former is
       intended for probes that can measure their targets all in one go, while
       the latter is for probing them one at a time, possibly in several
       concurrent subprocesses.

       At the moment, the only probes that use "Smokeping::probes::base" are
       the FPing derivatives. All the others use
       "Smokeping::probes::basefork", and chances are you should too. This
       document will thus concentrate on the latter case.


       The Smokeping::probes::skel module is a non-functional probe that is
       intended to make a good basis for a new probe module. Copy the file,
       "lib/probes/", to a new name and just fill out the blanks :)
       Note that the names of real probe modules must start with a capital


       The probe documentation is generated from the source code with the
       smokeping arguments "--man" or "--makepod". The embedded POD
       documentation should point to this real documentation, so that curious
       users of the "perldoc" command see what’s going on.  All the current
       probes do this.

       You should provide the method "pod_hash" that returns a reference to a
       hash with keys corresponding to the section names you want in the
       manpage. The supported section names are "name", "overview",
       "description", "authors", "notes", "bugs", and "see_also". If you don’t
       need a particular section, just leave it out.

       The special sections "synopsis" and "variables" are automatically
       generated from the description of your variables. See below.

       Note that if you use ’here documents’ (’<<’) that have POD markup
       inside, you should escape the markup so that it doesn’t show up in the
       embedded POD documentation. Most probes do it like this:

        my $e = "=";
        my $doc = <<DOC;
        ${e}head1 SECTION TITLE


       The probe should offer the "ProbeDesc" method that returns a short
       description of what it does. This will be used in the graphs produced
       by the web frontend.


       All Smokeping probes must define their variables by implementing a
       "probevars" method for probe-specific variables and a "targetvars"
       method for target-specific variables. If you don’t know the difference
       between these yet, see smokeping_examples.

       (The probes that are derived from "Smokeping::probes::base" don’t
       support target-specific variables, so they only use the "probevars"

       The base classes offer these methods too to provide the variables that
       are common to all the probes (eg. the probe-specific "step" variable
       and the target-specific "pings" variable. If you don’t want to add
       anything to the base class variables (perhaps because all your
       variables are of a target-specific nature, so you don’t need new probe-
       specific variables at all), you can leave the corresponding method out
       and it will be inherited from the base class.

       When you do supply your own "probevars" or "targetvars" method, you
       should combine your variables with those coming from the superclass.
       There is a convenience method called "_makevars" that does this, and
       the common idiom is

        sub probevars {
               my $class = shift;
               return $class->_makevars($class->SUPER::probevars, {
                       # your variables go here

       The variables are declared in a syntax that comes from the module used
       for parsing the configuration file, "Config::Grammar". Each variable
       should be a hash that uses the "special variable keys" documented in
       Config::Grammar. See "Smokeping::probes::skel" and the other probes for

       For reference, here are the keys the hash should have. Much of this is
       taken straight from the "Config::Grammar" manual.

       Keys you must provide
               Description of the variable.

               An example value. This will be used in the SYNOPSIS section in
               the probe manual.

       Optional keys
               A default value that will be assigned to the variable if none
               is specified or inherited.

           _re Regular expression upon which the value will be checked.

               String containing the returned error in case the regular
               expression doesn’t match (if not specified, a generic ’syntax
               error’ message will be returned).

               A function pointer. It is called for every value, with the
               value passed as its first argument. If the function returns a
               defined value it is assumed that the test was not successful
               and an error is generated with the returned string as content.

       The "probevars" and "targetvars" methods should return hash references
       that contain the variable names as keys and the hashes described above
       as values. In addition the "Config::Grammar" special section key
       "_mandatory" is supported and should contain a reference to a list of
       mandatory variables. The "_makevars" method is aware of this special
       key and merges the mandatory lists in its arguments. Note that no other
       "Config::Grammar" special section keys are supported.


       If you must do something at probe initialization time, like check that
       the external program you’re going to use behaves as you expect, you
       should do it in the "new" method. You should probably also take care
       that you don’t run the tests needlessly while in CGI mode. The usual
       way to do this is to test for $ENV{SERVER_SOFTWARE}. See the
       "Smokeping::probes::skel" module for an example.


       All the real action happens in the "pingone" method (or, for
       "Smokeping::probes::base"-derived probes, in the "ping" method.) The
       arguments for "pingone" are $self, the module instance (since this is a
       method) and $target, the target to be probed.

       You can access the probe-specific variables here via the
       "$self->{properties}" hash and the target-specific ones via the
       "$target->{vars}" hash. You get the number of pings needed for the
       target via the "pings" method: "my $count = $self->pings($target)".

       You should return a sorted array of the latency times measured. If a
       ping fails, don’t put anything in the array.

       That’s it, you’re done!


       If you would like to provide a documented example configuration for
       your probe (in addition to the automatically generated SYNOPSIS section
       in the probe manual), you can do so by adding it to the
       Smokeping::Examples module.  Look for the ’examples’ subroutine and add
       your example there.

       Future versions of Smokeping might provide a way to embed examples in
       the probe modules too. The author’s motivation for implementing this
       would be greatly increased by even a single demand for it, so please
       speak up if you think you’d use it.


       If you deal with timeouts (for example because your program offers a
       parameter for specifying the timeout for the pings), you should know a
       few things.

       First, there’s timeout logic in "Smokeping::probes::basefork" that
       kills the probe when the timeout is reached. By default the timeout is
       (# of pings * 5 seconds) + 1 second. If you expect that your pings can
       take longer, you should modify the default value of the probe-specific
       variable "timeout".  This would be done like this:

        sub probevars {
               my $class = shift;
               my $h = $class->SUPER::probevars;
               $h->{timeout}{_default} = 10; # override the superclass default
               return $class->_makevars($h, {
                       # your variables go here

       If you want to provide a target-specific "timeout" setting, you should
       delete the probe-specific variable and be sure to provide a default for
       your target-specific one. See eg. "Smokeping::probes::AnotherDNS" for
       an example of how this is done.

       Providing a target-specific "timeout" will make the timeout in
       "Smokeping::probes::basefork" be (# of pings * the maximum timeout of
       all targets) + 1 second. The 1 second is added so that the own timeout
       logic of the probe has time to kick in even in the worst case (ie. all
       pings are lost) before "Smokeping::probes::basefork" starts killing the


       Copyright 2005 by Niko Tyni.


       This program is free software; you can redistribute it and/or modify it
       under the terms of the GNU General Public License as published by the
       Free Software Foundation; either version 2 of the License, or (at your
       option) any later version.

       This program is distributed in the hope that it will be useful, but
       WITHOUT ANY WARRANTY; without even the implied warranty of
       General Public License for more details.

       You should have received a copy of the GNU General Public License along
       with this program; if not, write to the Free Software Foundation, Inc.,
       675 Mass Ave, Cambridge, MA 02139, USA.


       Niko Tyni <>


       This document makes writing new probes look much harder than it really


       The other Smokeping documents, especially smokeping_config.