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<title>Importing Custom Data</title>
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<center><h1>Importing Custom Data</h1></center>
<p>
<h3>Introduction</h3>
<p>
The mechanism for including custom recording/reporting code into collectl is very similar to that for
exporting custom data. One uses the switch <i>--import</i> followed by one or more file names, separated
by colons. Following each file name are one or more file-specific arguments which if specified are
comma separated as shown below:
<div class=terminal>
<pre>
collectl --import file1,d:file2
</pre></div>
In this example collectl will look for the files <i>file1.ph</i> and <i>file2.ph</i>, noting
that the first has the single argument 'd'. Collectl will execute a perl <i>require</i> on each
file (in the order they're specified) and subsequently call functions in them from various locations
within collectl. Looking for strings in both <i>collectl</i> and <i>formatit.ph</i> that begin
with <i>&{$imp</i> will identify the locations where collectl calls the functions named in the API
and may help during the development/testing process to better understand what collectl is doing.
<p>
As a reference, a simple module has been included in the same main directory as collectl itself,
which is named <i>hello.ph</i> as collectl's version of <i>Hello World</i>. Since it can't read
anything from /proc it is hardcoded to generate 3 lines of data with increasing data values. Beyond
that bit a hand-waving, everything else it does is fully functional. You can mix its output with
any standard collectl data, record to raw or plot files, play back the data and even send its output
over a socket.
<p>
From time to time additional <i>import</i> modules may be included in collectl which may also be used
as reference. For example, the module <i>misc.ph</i> is now also part of collectl. It imports data
about the uptime, number of people logged in, the cpu frequency and the number of mounted nfs file
systems.
<p>
It should be noted that although collectl itself does not use <i>strict</i>, which is a long story,
it is recommended these routines do. This will help ensure that they do not accidentally reuse a
variable of the same name that collectl does and accidentally step on it.
<p><b>A couple of words about performance</b>
<p>
One of the key design objectives for collectl is efficiency and it is indeed very lightweight,
typically using less than 0.2% of the CPU when sampling once every 10 seconds. Another way to
look at this is it often uses less than 192 CPU seconds in the course of an entire day.
If you care about overhead, and you should, be sure to be as efficient as you can in your own code.
If you have to run a command to get your data instead of reading it from /proc, that will be more
expensive. If that command has to do a lot of work, it will be even more expensive.
<p>
It is recommended your take advantage of collectl's
<a href=http://collectl.sourceforge.net/Performance.html>built-in mechanism</a> for
measuring its own performance. For example, measuring the performance of the <i>hello.ph</i> module,
which does almost nothing since it doesn't even look at /proc data, uses less than 1 second to read 8840
samples on an older 2GHz system, which is the equivalent of a full day's worth of sampling. Monitoring
CPU performance data take about 3-1/2 seconds and memory counters take about
7 seconds, just to give a few examples of the more efficient types of data it collects.
<p><h3>Access to collectl internal functions, variable and constants</h3>
<p>
Collectl is relatively big, at least for a perl script, consisting of over 100 internal subroutines,
most of which are simply for internal
housekeeping, but some of which are of a more general purpose. It also keeps most of its statistical
data in single variables and one dimensional arrays. Clearly hashes could make it more convenient
for passing data around but it was felt that the use of more complex data structures would generate
more overhead and so their use has been minimized.
<p>
While it is literally impossible to enumerate them all, there are a relatively small number of
functions, variables and constants that should be considered when writing your routines to
insure a more seamless integration with collectl. The following table is really only a means
to get started. If you need more details of what a function actually does or how a variable is used,
read the code.
<center>
<table border=1 width=75%>
<tr><td width=20%><b>Function</b></td><td><b>Definition</b></td></tr>
<tr><td>cvt()</td><td>Convert a string to a maximum number of characters, appending 'K', 'M', etc
as appropriate. Can also be instructed to divide counters by 1000 and sizes by 1024.</td></tr>
<tr><td>error()</td><td>Report error on terminal and if logging to a message file
write a type 'E' message. Then exit</td></tr>
<tr><td>fix()</td><td>When a counter turns negative, it has wrapped. This function will convert
to a positive number by adding back the size of a 32-bit word OR a user specified data width.</td></tr>
<tr><td>getexec()</td><td>Execute a command and record its output to a <i>raw file</i> when operating
in collectl mode, prepended with the supplied string</td</tr>
<tr><td>getproc()</td><td>Read data from /proc, prepending a string as with <i>getexec</i> except in
this case you can also instruct it to skip lines at the beginning or end. See the function itself
for details</td></tr>
<tr><td>record()</td><td>Only needed if not using <i>getproc</i>, which will call it for you. It writes
data to a <i>raw file> record when in record mode or calls the appropriate print routines in interactive
mode.
a single line of data</td></tr>
<tr><td width=20%><b>Variable</b></td><td><b>Definition</b></td></tr>
<tr><td>$datetime</td><td>The date/time stamp associated with the current set of data, in the user
requested format, based on the use of -o. See the constant <i>$miniFiller</i> which is a string of
spaces of the same width.</td></tr>
<tr><td>$intSecs</td><td>The number of seconds in the current interval. This is <i>not</i> an integer.</td></tr>
<tr><td width=20%><b>Constants</b></td><td><b>Definition</b></td></tr>
<tr><td>$miniFiller</td><td>A string of spaces, the same number of characters as in the
<i>$datetime</i> variable</td></td>
<tr><td>$rate</td><td>A text string that is set to <i>/secs</i> and appended to most of
the verbose format headers, indicating rates are being displayed. However, if the user specifies -on
with the collectl command to indicate non-normalized data, it is set to <i>/int</i> to indicate
per-interval data is being reported.</td></tr>
<tr><td>$SEP</td><td>This is the current plot format separator character, set to a space by default,
but can be changed with --sep so <i>never</i> hard code spaces into your plot format output.</td></tr>
</table>
</center>
<p>
<h3>The API</h3>
The API between collectl and user written code is actually a fixed number of callbacks. In other
words, when you tell collectl to import a piece of code, it not only uses that name to identify
the code it also uses that name as a qualifier on the name of the functions it calls.
If you load a module called <i>mymodule</i>, collectl will then make calls to <i>mymoduleInit(),
mymoduleGetData()</i> and several others as enumerated in the table below. You <i>must</i> include
all these function call backs in your code or prevent them from being called by restricting which
switches the user is allow to specify in the collectl command line. For example if your module
doesn't want to support plot data and you generate an error if the user specified -P (which can be
checked by examining <i>$plotFlag</i> in your init routine), you can safely leave off the
<i>PrintPlot</i> callback.
<p>
<center>
<table border=1 width=75%>
<tr><td width=20%><b>Function</b></td><td><b>Definition</b></td></tr>
<tr><td>Analyze</td><td>Examine performance counters and generate values for current interval</td></tr>
<tr><td>GetData</td><td>Read performance data from /proc or any other mechanism of choice</td></tr>
<tr><td>GetHeader</td><td>During playback only, supply the header for additional initialization</td></tr>
<tr><td>Init</td><td>One time initializations are performed here</td></tr>
<tr><td>InitInterval<td>Initializations required for each processing cycle</td></tr>
<tr><td>IntervalEnd<td>Optional routine, called at end of each processing cycle if defined</td></tr>
<tr><td>PrintBrief</td><td>Build output strings for brief format</td></tr>
<tr><td>PrintExport</td><td>Build output strings for formatting by gexpr, lexpr and sexpr, which are
3 standard collectl <i>--export</i> modules</td></tr>
<tr><td>PrintPlot</td><td>Build output string in plot format</td></tr>
<tr><td>PrintVerbose</td><td>Build output string in verbose format</td></tr>
<tr><td>UpdateHeader</td><td>Add custom line(s) to all file headers</td></tr>
</table>
</center>
<p>
There are also several constants that must be passed back to collectl during intialization.
See <i>Init()</i> for more details.
<p>
<ul>
<li>A string consisting of 's', 'd', or 'sd', indicating whether or not this module supports
<i>summary data, detail data</i> or <i>both</i>.
<li>A unique string for any data collected by this code and ultimately
passed to collectl in <i>record()</i>. As a result, all data written to the raw file will be
prepended by this discriminator so that during actual collection and/or playback collectl will know
to call the analysis routine upon seeing this type of data. Therefore this string must be unique
with respect to any other data collection qualification strings. This string will also be used as an
extension for any detail plot files and so should be on the order of 3 or 4 characters long.</li>
</ul>
<p><b>Analyze($type, \$data)</b>
<p>
This function is called for each line of recorded data that begins with the qualifier string that
has been set in <i>Init</i>. Any lines that don't begin with that string will never be seen by
this routine. You should also be sure that string is unque enough that you aren't passed data
you don't expect.
<ul>
<li><b>$type</b> is the first space-separated field from the recorded data. It is completely under
your control to decide how to process that data. In some cases there will only be a single line to
process and no further decisions will be required. In other cases there
may be multiple lines and it may be necessary to include an additional discriminator when recording the
data so that the analysis routine can figure out what to do with it. For example, try running with
-d4 and look at the data returned for -sf or -si.
<li><b>$data</b> is a reference to the string of everything that follows <i>$type</i> in the current
line of data being processed</li>
</ul>
<p><b>GetData()</b>
<p>
This function takes no arguments and is responsible for reading in the data to be recorded
and processed by collectl and as such you should strive to make it as efficient as possible.
If reading data from /proc, you can probably use the getproc()
function, using 0 as the first parameter for doing generic reads. If you wish to execute
a command, you can call getexec() and pass it a 3 which is its generic argument for capturing
the entire contents of whatever command is being executed.
<p>
If you want to <i>do your own thing</i> you can basically do anything you want, but be sure
to call <i>record()</i> to actually write the data to the raw file and optionally
pass it to the analysis routine later on.
<p>
In any case, each record <i>must</i> use the same discriminator that <i>Analyze</i> is expecting
so collectl can identify that data as coming from this module. You may
also want to look at the data gathering loop inside of collectl to get a better feel for
how data collection works in general.
<p>
To make sure you're collecting data correctly, run collectl with -d4 as shown below for reading
socket data, which uses the string <i>sock</i> as its own discriminator. The <i>Analyze</i>
routine then needs to look at the second field to identify how to interpret the remainder of
the data line.
<div class=terminal>
<pre>
collectl -ss -d4
>>> 1238001124.002 <<<
sock sockets: used 405
sock TCP: inuse 10 orphan 0 tw 0 alloc 12 mem 0
sock UDP: inuse 8 mem 0
sock RAW: inuse 0
sock FRAG: inuse 0 memory 0
</pre></div>
<p><b>GetHeader(\$header)</b>
<p>
This function is called when one needs to know what is stored in the header of a file being
played back - it is only called if collectl doesn't find it and therefore optional.
While it is impossible to know how a module will use <i>GetHeader</i>, it is often used to
retrieve instance numbers, such as how many nvidia GPUs one might have been monitored or
their type (see <i>nvidia.ph</i>), both of which would have been written to the header
using a call to
<i>UpdateHeader</i>.
<ul>
<li><b>$header</b> is a reference to the header once it is read in collectl's <i>initFormat</i></li>
</ul>
<p>
Since standard collectl processing is to always playback what the user requests, even if
that data hadn't even been collected, the same holds true here. If one had gotten to
this point and it is determined there is no data, the API does not contain a failure return
code as does <i>init</i>. Rather, one would simply end up reporting 0s for all values.
<p><b>Init(\$options, \$key)</b>
<p>
This function is called once by collectl, before any data collection begins. If there are any
one-time initializations of variables to do, this is the place to do them. For example, when processing
incrementing variables one often subtracts the previous value from the current one and this is the
ideal place to initialize their previous values to 0. Naturally that will lead to erroneous results
for the first interval, which is why collectl never includes those stats in its output. However, if
you don't initialize them to something you will get <i>uninitialized variable</i> warnings the first
time they're used.
<ul>
<li><b>$options</b> is a reference to the option string, if any, passed immediately
after the name following<i>--import</i> and specifies whether the user wants to see
<i>summary data, detail data</i> or <i>both</i>. If none specified it must be set to the
default behavior desired for this module, typically 's'.</li>
<li><b>$key</b> is a reference to a string of usually 2-4 characters which will be
prepended to each data record and used in several places to associate data records with
this module</li>
</ul>
<p>
Upon completion return 1 to indicate <i>success</i>, Returning a -1 will indicate <i>failure</i>
and result in the imported module's functional calls to be removed from collectl's call
stack and will no longer be actively called.
<p><b>InitInterval()</b>
<p>
During each data collection interval, collectl may need to reset some counters. For example, when
processing disk data, collectl adds together all the disk stats for each interval which are then
reported as summary data. At the beginning of each interval these counters must be reset to 0
and it's at that point in the processing that this routine is called.
<p><b>IntervalEnd()</b>
<p>
As described earlier, if this routine exists it is called at the end of an interval processing cycle.
This makes it possible to do any post processing that may be require before the start of the next
interval. In many cases this is not necessary.
<p><b>PrintBrief($type, \$line)</b>
<p>
The trick with brief mode is that that multiple types of data are displayed together on the same line.
That means each imported module must append its own unique data to the current line of output as it
is being constructed without any carriage returns. Further, since there are 2 header lines and
<i>brief format</i> supports the ability to print running totals when one enters <i>return</i> during
processing, there are a number of places one needs to have their code called from.
<p>
<ul>
<li><b>$type</b> is an integer from 1 to 6 and is used to decide which subfunction to execute.
Think of it this a <i>case statement</i> control variable.
<li><b>$line</b> is a reference to the current output line being constructed. Simply append
whatever makes sense for that function, be it a header or a value. In the case of the running
totals, since that is always printed on the terminal and never goes to a socket a simple
<i>print</i> is sufficient.
</ul>
<p><b>PrintExport($type, \$ref1, \$ref2, \$ref3, \$ref4)</b>
<p>
What about custom export modules and how this effects them?
The good news is that at least for the standard 3, <i>sexpr, lexpr</i> and the newest
<i>gexpr</i> all support <i>--import</i>. In other words they too have callbacks that you must respond
to if your code is being run at the same time as one of these.
<p>
Again, see <i>hello.ph</i> for an example, but suffice it to say you need to do something when
called, even if only a null function is supplied.
<p>
Since both <i>lexpr</i> and <i>sexpr</i> can write their output to the terminal, the easiest way
to test these is to just run collect and have it display on the terminal. However, the output
of gexpr is binary and so the easiest way to test this code is to tell it not to open a socket
(though you must supply an address/port, even if invalid) and report the 3 data elements it is about to
encode by running with a debug value of 9 noting this is <i>gexpr's</i> own internal debug
switch and not collectl's. The 8 bit tells gexpr to <i>not</i> open the sockeT (which is why an
invalid value is ok) and the 1 bit tells it to display its output nicely formatting on the terminal.
<div class=terminal>
<pre>
collectl --import hello --export gexpr,1.2.3.4:5,d=9
Name: hwtotals.hw Units: num/sec Val: 140
Name: hwtotals.hw Units: num/sec Val: 230
Name: hwtotals.hw Units: num/sec Val: 320
</pre></div>
<p>
<ul>
<li><b>$type</b> is a 'g', 'l' or 's' depending which of the 3 <i>expr</i> modules is exported and the
interpretation of the 4 references that follow are type dependent</li>
<li><b>type=g</b></li>
<ul>
<li><b>$ref1</b> is the data label</li>
<li><b>$ref2</b> is the units string</li>
<li><b>$ref3</b> is data value</li>
</ul>
<li><b>type=l</b></li>
<ul>
<li><b>$ref1</b> is the summary data label</li>
<li><b>$ref2</b> is the summary data value</li>
<li><b>$ref3</b> is the detail data label</li>
<li><b>$ref4</b> is the detail data value</li>
</ul>
<li><b>type=s</b></li>
<ul>
<li><b>$ref1</b> is the summary data line</li>
<li><b>$ref1</b> is the detail data line</li>
</ul>
</ul>
<p><b>PrintPlot($type, \$line)</b>
<p>
This type of output is formatted for plotting, which can get quite complicated
based on whether you are writing to a terminal, multiple files or a socket. Fortunately
all that headache is handled for you by collectl. All you need to do is append your
<i>summary</i> or <i>detail</i> data to the current line being constructed, similar
to the way brief data is handled. Since it has to handle both headers as well as data,
there are 4 <i>types</i> included in the call.
<p>
<ul>
<li><b>$type</b> is used as a selector to specify whether header/data and if for summary/detail
is to be constructed.</li>
<li><b>$line</b> is a reference to the current line being constructed. Be sure to use $SEP as
a field separator so your code will correctly use collectl's <i>--sep</i> switch.
</ul>
<p><b>PrintVerbose($printHeader, $homeFlag, \$line)</b>
<p>
Like <i>PrintBrief</i>, this routine is in charge of printing verbose data but is much simpler
since it doesn't have to insert code into the middle of running strings.
<p>
<ul>
<li><b>$printHeader</b> is actually a flag, which when set indicate it's time to print a header.
As you can see in hello.ph, there are 2 global string worth knowing about. Both <i>$miniFiller</i>
and <i>$datetime</i> are normally set to null, but if the user specifies a time switch such as -oT,
the first will be set to the appropriate number of pad characters and the second set to the time
in the format specified by -o.
<li><b>$homeFlag</b> is a localized copy of collectl's $homeFlag which when set indicates the
display is in <i>home</i> mode and section separating <i>returns</i> should be omitted from the
output to make it more dense.</li>
<li><b>$line</b> is a reference to the line about to be printed. Set it to the you wish to print,
rather than append to it.
</ul>
<p><b>UpdateHeader(\$line)</b>
<p>
<ul>
<li><b>$line</b> is a reference to the string that contains the standard header that
appears at the beginning of all collectl files. This call is made immediately before
writing out the final line of #s and so anything appended to this string will appear in
the header as its own unique line. If you do not want to add anything to the header
simply make this an empty function.</li>
</ul>
<table width=100%><tr><td align=right><i>updated Feb 21, 2011</i></td></tr></colgroup></table>
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