path: root/doc/SystemTap_Beginners_Guide/en-US/Scripts.xml

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<section id="scripts">
  <title>SystemTap Scripts</title>
<indexterm>
<primary>scripts</primary>
<secondary>introduction</secondary>
</indexterm>	
 <indexterm>
<primary>SystemTap scripts</primary>
<secondary>introduction</secondary>
</indexterm> 



<para>
    For the most part, SystemTap scripts are the foundation of each SystemTap
    session. SystemTap scripts instruct SystemTap on what type of information to
    collect, and what to do once that information is collected.
  </para>
<indexterm>
<primary>scripts</primary>
<secondary>introduction</secondary>
<tertiary>components</tertiary>
</indexterm>
<indexterm>
<primary>SystemTap scripts</primary>
<secondary>introduction</secondary>
<tertiary>components</tertiary>
</indexterm>

<indexterm>
	<primary>components</primary>
	<secondary>SystemTap scripts</secondary>
	<tertiary>introduction</tertiary>
</indexterm>

<indexterm>
<primary>scripts</primary>
<secondary>introduction</secondary>
<tertiary>events and handlers</tertiary>
</indexterm>
<indexterm>
<primary>SystemTap scripts</primary>
<secondary>introduction</secondary>
<tertiary>events and handlers</tertiary>
</indexterm>
<indexterm>
<primary>handlers and events</primary>
<secondary>SystemTap scripts</secondary>
<tertiary>introduction</tertiary>
</indexterm>
  <para>
    As stated in <xref linkend="understanding-how-systemtap-works"/>, SystemTap
    scripts are made up of two components: <emphasis>events</emphasis> and
    <emphasis>handlers</emphasis>. Once a SystemTap session is underway,
    SystemTap monitors the operating system for the specified events and
    executes the handlers as they occur.
  </para>

  <note>
    <title>Note</title>
<indexterm>
<primary>scripts</primary>
<secondary>introduction</secondary>
<tertiary>probes</tertiary>
</indexterm>
<indexterm>
<primary>SystemTap scripts</primary>
<secondary>introduction</secondary>
<tertiary>probes</tertiary>
</indexterm>
<indexterm>
<primary>probes</primary>
<secondary>SystemTap scripts</secondary>
<tertiary>introduction</tertiary>
</indexterm>
    <para>
      An event and its corresponding handler is collectively called a
      <emphasis>probe</emphasis>. A SystemTap script can have multiple probes.
    </para>
	
    <para>
      A probe's handler is commonly referred to as a <emphasis>probe
      body</emphasis>.
    </para>
  </note>

  <para>
    In terms of application development, using events and handlers is similar to
    instrumenting the code by inserting diagnostic print statements in a
    program's sequence of commands. These diagnostic print statements allow you
    to view a history of commands executed once the program is run.
  </para>
<!--	<para>
		In terms of application development, using events and handlers is similar to inserting <command>print</command> statements in a program's sequence of commands. These <command>print</command> statements allow you to view a history of commands executed once the program is run. 
	</para>	-->
	
  <para>
    SystemTap scripts allow insertion of the instrumentation code without
    recompilation of the code and allows more flexibility with regard to
    handlers. Events serve as the triggers for handlers to run; handlers can be
    specified to record specified data and print it in a certain manner.
  </para>
	
  <formalpara id="scriptformats">
    <title>Format</title>
<indexterm>
<primary>scripts</primary>
<secondary>introduction</secondary>
<tertiary>format and syntax</tertiary>
</indexterm>
<indexterm>
<primary>SystemTap scripts</primary>
<secondary>introduction</secondary>
<tertiary>format and syntax</tertiary>
</indexterm>
<indexterm>
<primary>format and syntax</primary>
<secondary>SystemTap scripts</secondary>
<tertiary>introduction</tertiary>
</indexterm>
<indexterm>
<primary>syntax and format</primary>
<secondary>SystemTap scripts</secondary>
<tertiary>introduction</tertiary>
</indexterm>
    <para>
      SystemTap scripts use the file extension <filename>.stp</filename>, and
      contains probes written in the following format:
    </para>
  </formalpara>	
<screen>
probe	<replaceable>event</replaceable> {<replaceable>statements</replaceable>}
</screen>

  <para>
    SystemTap supports multiple events per probe; multiple events are delimited
    by a comma (<command>,</command>). If multiple events are specified in a
    single probe, SystemTap will execute the handler when any of the specified
    events occur.
  </para>
<indexterm>
<primary>scripts</primary>
<secondary>introduction</secondary>
<tertiary>statement blocks</tertiary>
</indexterm>  
<indexterm>
<primary>SystemTap scripts</primary>
<secondary>introduction</secondary>
<tertiary>statement blocks</tertiary>
</indexterm>
<indexterm>
<primary>statement blocks</primary>
<secondary>SystemTap scripts</secondary>
<tertiary>introduction</tertiary>
</indexterm>
  <para>
	Each probe has a corresponding <firstterm>statement block</firstterm>. This statement block is 
	enclosed in braces (<command>{ }</command>) and contains the statements to be executed per event. 
	SystemTap executes these statements in sequence; special separators or 
	terminators are generally not necessary between multiple statements.
  </para>

<note>
	<title>Note</title>
	<para>
		Statement blocks in SystemTap scripts follow the same syntax and semantics as the C 
		programming language. A statement block can be nested within another statement block.
  	</para>
</note>	
<indexterm>
<primary>scripts</primary>
<secondary>introduction</secondary>
<tertiary>functions</tertiary>
</indexterm>
<indexterm>
<primary>SystemTap scripts</primary>
<secondary>introduction</secondary>
<tertiary>functions</tertiary>
</indexterm>
<indexterm>
<primary>functions</primary>
<secondary>SystemTap scripts</secondary>
<tertiary>introduction</tertiary>
</indexterm>
  <para>
    Systemtap allows you to write functions to factor out code to be used by a
    number of probes. Thus, rather than repeatedly writing the same 
    series of statements in multiple probes, you can just place the instructions
    in a <firstterm>function</firstterm>, as in:
  </para>

<screen>
function <replaceable>function_name</replaceable>(<replaceable>arguments</replaceable>) {<replaceable>statements</replaceable>}
probe <replaceable>event</replaceable> {<replaceable>function_name</replaceable>(<replaceable>arguments</replaceable>)}
</screen>

  <para>
    The <command><replaceable>statements</replaceable></command> in
    <replaceable>function_name</replaceable> are executed when the probe for
    <replaceable>event</replaceable> executes. The
    <replaceable>arguments</replaceable> are optional values passed into the
    function.
  </para>

<!--
	<para>The <replaceable>exit()</replaceable> condition is optional; this condition safely terminates the session once the script successfully collects the required information the first time.</para>	
	-->
  <important>
    <title>Important</title>
    <para>
      <xref linkend="scripts"/> is designed to introduce readers to the basics
      of SystemTap scripts. To understand SystemTap scripts better, it is
      advisable that you refer to <xref linkend="useful-systemtap-scripts"/>;
      each section therein provides a detailed explanation of the script, its
      events, handlers, and expected output.
    </para>
  </important>

  <section id="systemtapscript-events">
    <title>Event</title>
<indexterm>
<primary>Events</primary>
<secondary>introduction</secondary>
</indexterm>	
    <para>
      SystemTap events can be broadly classified into two types:
      <firstterm>synchronous</firstterm> and
      <firstterm>asynchronous</firstterm>.
    </para>

    <formalpara>
      <title>Synchronous Events</title>
<indexterm>
<primary>Events</primary>
<secondary>synchronous events</secondary>
</indexterm>

<indexterm>
<primary>synchronous events</primary>
<secondary>Events</secondary>
</indexterm>
      <para>
	A <firstterm>synchronous</firstterm> event occurs when any process
	executes an instruction at a particular location in kernel
	code. This gives other events a reference point from which more
	contextual data may be available.
      </para>
    </formalpara>

<!--<para>A <firstterm>synchronous</firstterm> event occurs when any processor executes an instruction matched by the specification. This gives other events a reference point (or instruction address) from which more contextual data may be available.</para>-->

<!--<para>Synchronous events reference particular locations in kernel code. As a result, when synchronous events are used SystemTap can determine contextual  information regarding the location (such as function parameters).</para>-->
<indexterm>
<primary>Events</primary>
<secondary>examples of synchronous and asynchronous events</secondary>
</indexterm>

<indexterm>
<primary>examples of synchronous and asynchronous events</primary>
<secondary>Events</secondary>
</indexterm>
    <para>Examples of synchronous events include:</para>

<variablelist>

<varlistentry>
	<term>syscall.<replaceable>system_call</replaceable></term>
	<listitem>
<indexterm>
<primary>Events</primary>
<secondary><command>syscall.<replaceable>system_call</replaceable></command></secondary>
</indexterm>

<indexterm>
<primary><command>syscall.<replaceable>system_call</replaceable></command></primary>
<secondary>Events</secondary>
</indexterm>

	  <para>
	    The entry to the system call
	    <replaceable>system_call</replaceable>. If the exit from a syscall
	    is desired, appending a <command>.return</command> to the event
	    monitor the exit of the system call instead. For example, to specify
	    the entry and exit of the system call <command>close</command>, use 
	    <command>syscall.close</command> and
	    <command>syscall.close.return</command> respectively.
	  </para>
	</listitem>	
</varlistentry>
	
<varlistentry>
	<term>vfs.<replaceable>file_operation</replaceable></term>
	<listitem>
<indexterm>
<primary>Events</primary>
<secondary><command>vfs.<replaceable>file_operation</replaceable></command></secondary>
</indexterm>

<indexterm>
<primary><command>vfs.<replaceable>file_operation</replaceable></command></primary>
<secondary>Events</secondary>
</indexterm>

	  <para>
	    The entry to the <replaceable>file_operation</replaceable> event for
	    Virtual File System (VFS). Similar to <command>syscall</command>
	    event, appending a <command>.return</command> to the event monitors
	    the exit of the <replaceable>file_operation</replaceable> operation.
	  </para>
	</listitem>	
</varlistentry>
	
<varlistentry>
	<term>kernel.function("<replaceable>function</replaceable>")</term>
	<listitem>
<indexterm>
<primary>Events</primary>
<secondary><command>kernel.function("<replaceable>function</replaceable>")</command></secondary>
</indexterm>

<indexterm>
<primary><command>kernel.function("<replaceable>function</replaceable>")</command></primary>
<secondary>Events</secondary>
</indexterm>
	  <para>
	    The entry to the kernel function
	    <replaceable>function</replaceable>. For example,
	    <command>kernel.function("sys_open")</command> refers to the "event"
	    that occurs when the kernel function <command>sys_open</command> is
	    called by any thread in the system. To specify the
	    <emphasis>return</emphasis> of the kernel function
	    <command>sys_open</command>, append the <command>return</command>
	    string to the event statement;
	    i.e. <command>kernel.function("sys_open").return</command>.
	  </para>
<indexterm>
<primary>Events</primary>
<secondary>wildcards</secondary>
</indexterm>

<indexterm>
<primary>wildcards in events</primary>
</indexterm>
<indexterm>
	<primary>events wildcards</primary>
</indexterm>
	  <para>
	    When defining probe events, you can use asterisk (<literal>*</literal>)
	    for wildcards. You can also trace the entry or exit of a function in
	    a kernel source file. Consider the following example:
	  </para>

<example id="wildcards">
<title>wildcards.stp</title>
<programlisting>
probe kernel.function("*@net/socket.c") { }
probe kernel.function("*@net/socket.c").return { }
</programlisting>	
</example>

	  <remark>Wild cards also work for other types of events, e.g. syscall.*</remark>

	  <para>
	    In the previous example, the first probe's event specifies the entry
	    of ALL functions in the kernel source file
	    <filename>net/socket.c</filename>. The second probe specifies the
	    exit of all those functions. Note that in this example, 
	    there are no statements in the handler;
	    as such, no information will be collected or displayed.
	  </para>
	</listitem>

      </varlistentry>

      <varlistentry>
	<term>kernel.trace("<replaceable>tracepoint</replaceable>")</term>
	<listitem>
<indexterm><primary>tracepoint</primary></indexterm>
<indexterm>
<primary>Events</primary>
<secondary><command>kernel.trace("<replaceable>tracepoint</replaceable>")</command></secondary>
</indexterm>

<indexterm>
<primary><command>kernel.trace("<replaceable>tracepoint</replaceable>")</command></primary>
<secondary>Events</secondary>
</indexterm>
	  <para>
	    The static probe for <replaceable>tracepoint</replaceable>.
	    Recent kernels (2.6.30 and newer)
	    include instrumentation for specific events in the kernel. These
	    events are statically marked with tracepoints.  One example of a
	    tracepoint available in systemtap is
	    <command>kernel.trace("kfree_skb")</command> which indicates each
	    time a network buffer is freed in the kernel.
	  </para>
	</listitem>

      </varlistentry>

      <varlistentry>
	<term>module("<replaceable>module</replaceable>").function("<replaceable>function</replaceable>")</term>
	<listitem>
<indexterm>
<primary>Events</primary>
<secondary><command>module("<replaceable>module</replaceable>")</command></secondary>
</indexterm>

<indexterm>
	<primary><command>module("<replaceable>module</replaceable>")</command></primary>
<secondary>Events</secondary>
</indexterm>
	  <para>Allows you to probe functions within modules. For example:</para>
		
<example id="eventsmodules"><title>moduleprobe.stp</title>
<programlisting>
probe module("ext3").function("*") { }
probe module("ext3").function("*").return { }
</programlisting>	
</example>
		
		<para>
			The first probe in <xref linkend="eventsmodules"/>
		points to the entry of <emphasis>all</emphasis> functions for
		the <filename>ext3</filename> module. The second probe points to
		the exits of all functions for that same module; the use of the
		<command>.return</command> suffix is similar to
		<command>kernel.function()</command>. Note that the probes in
		<xref linkend="eventsmodules"/> do not contain statements
		in the probe handlers, and as such will not print any useful
		data (as in <xref linkend="wildcards"/>).
	        </para>
		
		<para>
			A system's kernel modules are typically located in <filename>/lib/modules/<replaceable>kernel_version</replaceable></filename>, where <replaceable>kernel_version</replaceable> refers to the currently loaded kernel version. Modules use the filename extension <filename>.ko</filename>. 
		</para>	
		
	</listitem>
      </varlistentry>
    </variablelist>

    <formalpara>
      <title>Asynchronous Events</title>
<indexterm>
<primary>Events</primary>
<secondary>asynchronous events</secondary>
</indexterm>

<indexterm>
<primary>asynchronous events</primary>
<secondary>Events</secondary>
</indexterm>

      <para>
	<firstterm>Asynchronous</firstterm> events are not tied to a particular
	instruction or location in code. This family of probe points consists
	mainly of counters, timers, and similar constructs.
      </para>
<!--	<para><firstterm>Asynchronous</firstterm> events, on the other hand, do not point to any reference point. This family of probe points consists mainly of counters, timers, and similar constructs.</para>-->
    </formalpara>

    <para>Examples of asynchronous events include:</para>

    <variablelist>

      <varlistentry>
	<term>begin</term>
	<listitem>
<indexterm>
<primary>Events</primary>
<secondary><command>begin</command></secondary>
</indexterm>

<indexterm>
<primary><command>begin</command></primary>
<secondary>Events</secondary>
</indexterm>		
	  <para>
	    The startup of a SystemTap session; i.e. as soon as the SystemTap
	    script is run.
	  </para>
	</listitem>	
      </varlistentry>	

      <varlistentry>
	<term>end</term>
	<listitem>
<indexterm>
<primary>Events</primary>
<secondary><command>end</command></secondary>
</indexterm>

<indexterm>
<primary><command>end</command></primary>
<secondary>Events</secondary>
</indexterm>
	  <para>The end of a SystemTap session.</para>
	</listitem>	
      </varlistentry>
      <varlistentry>
	<term>timer events</term>
	<listitem>
<indexterm>
<primary>Events</primary>
<secondary>timer events</secondary>
</indexterm>

<indexterm>
<primary>timer events</primary>
<secondary>Events</secondary>
</indexterm>

	  <para>
	    An event that specifies a handler to be executed periodically.
	    For example:
	  </para>
		
<example id="timer"><title>timer-s.stp</title>
<programlisting>
probe timer.s(4)
{
  printf("hello world\n")
}
</programlisting>
</example>

	  <para>
	    <xref linkend="timer"/> is an example of a probe that prints
	    <command>hello world</command> every 4 seconds. Note that you can
	    also use the following timer events:
	  </para>
	
<itemizedlist>
<listitem><para><command>timer.ms(<replaceable>milliseconds</replaceable>)</command></para></listitem>

<listitem><para><command>timer.us(<replaceable>microseconds</replaceable>)</command></para></listitem>

<listitem><para><command>timer.ns(<replaceable>nanoseconds</replaceable>)</command></para></listitem>

<listitem><para><command>timer.hz(<replaceable>hertz</replaceable>)</command></para></listitem>

<listitem><para><command>timer.jiffies(<replaceable>jiffies</replaceable>)</command></para></listitem>
</itemizedlist>

	  <para>
	    When used in conjunction with other probes that collect information,
	    timer events allows you to print out get periodic updates and see
	    how that information changes over time.
	  </para>

	</listitem>
      </varlistentry>

  </variablelist>

    <important>
      <title>Important</title>
      <para>
	SystemTap supports the use of a large collection of probe events. For
	more information about supported events, refer to <command>man
	stapprobes</command>. The <citetitle>SEE ALSO</citetitle> section of
	<command>man stapprobes</command> also contains links to other
	<command>man</command> pages that discuss supported events for specific
	subsystems and components.
      </para>
    </important>

<remark>is reference appropriate? too advanced for readers (it seems so to me)? please advise.</remark> 

  </section>
<!-- stophere -->
<section id="systemtapscript-handler">
	<title>Systemtap Handler/Body</title>
	<indexterm>
		<primary>handlers</primary>
		<secondary>introduction</secondary>
	</indexterm>
	<para> Consider the following sample script: </para>
	
<example id="helloworld"><title>helloworld.stp</title>
<programlisting>
probe begin
{
  printf ("hello world\n")
  exit ()
}
</programlisting>	
</example>
	
	<para>
		In <xref linkend="helloworld"/>, the event <command>begin</command>
		(i.e. the start of the session) triggers the handler enclosed in
		<command>{ }</command>, which simply prints <command>hello
			world</command> followed by a new-line, then exits.
	</para>	
	
	<note>
		<title>Note</title>
		<indexterm>
			<primary>functions (used in handlers)</primary>
			<secondary><command>exit()</command></secondary>
		</indexterm>
		
		<indexterm>
			<primary><command>exit()</command></primary>
			<secondary>functions</secondary>
		</indexterm>
		<para>
			SystemTap scripts continue to run until the
			<command>exit()</command> function executes. If the users wants to stop
			the execution of the script, it can interrupted manually with
			<keycombo><keycap>Ctrl</keycap><keycap>C</keycap></keycombo>.
		</para>
	</note>
	
	<formalpara id="printf">
		<title>printf ( ) Statements</title>
		<indexterm>
			<primary><command>printf()</command></primary>
			<secondary>format strings</secondary>
		</indexterm>
		
		<para>
			The <command>printf ()</command> statement is one of the simplest
			functions for printing data. <command>printf ()</command> can also be
			used to display data using a wide variety of SystemTap functions in the
			following format:
		</para>
	</formalpara>
	
	
	<programlisting>
		printf ("<replaceable>format string</replaceable>\n", <replaceable>arguments</replaceable>)
	</programlisting>
	<indexterm>
		<primary><command>printf()</command></primary>
		<secondary>format strings</secondary>
	</indexterm>
	
	<indexterm>
		<primary>format strings</primary>
		<secondary><command>printf()</command></secondary>
	</indexterm>
	<para>
		The <replaceable>format string</replaceable> specifies how
		<replaceable>arguments</replaceable> should be printed. The format string
		of <xref linkend="helloworld"/> simply instructs SystemTap to print
		<command>hello world</command>, and contains no format specifiers.
	</para>
	<indexterm>
		<primary><command>printf()</command></primary>
		<secondary>format specifiers</secondary>
	</indexterm>
	
	<indexterm>
		<primary>format specifiers</primary>
		<secondary><command>printf()</command></secondary>
	</indexterm>
	<para>
		You can use the format specifiers <command>%s</command> (for strings)
		and <command>%d</command> (for numbers) in format strings, depending on
		your list of arguments. Format strings can have multiple format
		specifiers, each matching a corresponding argument; multiple arguments
		are delimited by a comma (<command>,</command>).
	</para>
	
	<note>
		<title>Note</title>
		<indexterm>
			<primary><command>printf()</command></primary>
			<secondary>syntax and format</secondary>
		</indexterm>
		
		<indexterm>
			<primary>syntax and format</primary>
			<secondary><command>printf()</command></secondary>
		</indexterm>
		<indexterm>
			<primary>format and syntax</primary>
			<secondary><command>printf()</command></secondary>
		</indexterm>
		<para>Semantically, the SystemTap <command>printf</command> function is
			very similar to its C language counterpart. The aforementioned syntax
			and format for SystemTap's <command>printf</command> function is
			identical to that of the C-style <command>printf</command>.
		</para>
	</note>
	
	<para> To illustrate this, consider the following probe example: </para>
	
<example id="syscall-open">
<title>variables-in-printf-statements.stp</title>
<programlisting>
probe syscall.open
{
  printf ("%s(%d) open\n", execname(), pid())
}
</programlisting>
</example>
	
	<para>
		<xref linkend="syscall-open"/> instructs SystemTap to probe all entries to
		the system call <command>open</command>; for each event, it prints the
		current <command>execname()</command> (a string with the executable name) and
		<command>pid()</command> (the current process ID number), followed by the word
		<command>open</command>. A snippet of this probe's output would look like:
	</para>
	
	<remark>editorial review: does a clarification that "format specifier1" is
		to "argument1", "format specifier2" is to "argument2", or is this clear
		enough? </remark>
	
<screen>
vmware-guestd(2206) open
hald(2360) open
hald(2360) open
hald(2360) open
df(3433) open
df(3433) open
df(3433) open
hald(2360) open
</screen>
	
	<formalpara id="systemtapscript-functions">
		<title>SystemTap Functions</title>
		<indexterm>
			<primary>functions</primary>
		</indexterm>
		
		<indexterm>
			<primary>SystemTap script functions</primary>
		</indexterm>
		
		<indexterm>
			<primary>handler functions</primary>
		</indexterm>
		
		<para>
			SystemTap supports a wide variety of functions that can be used as
			<command>printf ()</command> arguments. <xref linkend="syscall-open"/>
			uses the SystemTap functions <command>execname()</command> (name of the
			process that called a kernel function/performed a system call) and
			<command>pid()</command> (current process ID).
		</para>
	</formalpara>		
	
	<remark>is "handler function" an appropriate term? wcohen: use "SystemTap functions" to match up language in man pages</remark>
	
	<para>The following is a list of commonly-used SystemTap functions:</para>	
	<variablelist>
		
		<varlistentry>
			<term>tid()</term>
			<listitem>
				<indexterm>
					<primary>functions</primary>
					<secondary><command>tid()</command></secondary>
<!-- 					<tertiary><command>tid()</command></tertiary> -->
				</indexterm>
				
				<indexterm>
					<primary>functions</primary>
					<secondary><command>tid()</command></secondary>
<!-- 					<tertiary></tertiary> -->
				</indexterm>
				
				<indexterm>
					<primary><command>tid()</command></primary>
					<secondary>functions</secondary>
<!-- 					<tertiary>handler </tertiary> -->
				</indexterm>
				
				<para>The ID of the current thread.</para>
			</listitem>	
		</varlistentry>	
		
		<varlistentry>
			<term>uid()</term>
			<listitem>
				<indexterm>
					<primary>functions</primary>
					<!--<secondary>handler functions</secondary>-->
					<secondary><command>uid()</command></secondary>
				</indexterm>
<!--				
				<indexterm>
					<primary>handler functions</primary>
					<secondary>Handlers</secondary>
					<tertiary><command>uid()</command></tertiary>
				</indexterm>
				-->
				<indexterm>
					<primary><command>uid()</command></primary>
					<secondary>functions</secondary>
<!-- 					<tertiary>handler functions</tertiary> -->
				</indexterm>
				<para>The ID of the current user.</para>
			</listitem>	
		</varlistentry>
		
		<varlistentry>
			<term>cpu()</term>
			<listitem>
				<indexterm>
					<primary>functions</primary>
					<!--<secondary>handler functions</secondary>-->
					<secondary><command>cpu()</command></secondary>
				</indexterm>
<!--				
				<indexterm>
					<primary>handler functions</primary>
					<secondary>Handlers</secondary>
					<tertiary><command>cpu()</command></tertiary>
				</indexterm>
				-->
				<indexterm>
					<primary><command>cpu()</command></primary>
					<secondary>functions</secondary>
<!-- 					<tertiary>handler functions</tertiary> -->
				</indexterm>		
				<para>The current CPU number.</para>
			</listitem>	
		</varlistentry>
		
		<varlistentry>
			<term>gettimeofday_s()</term>
			<listitem>
				<indexterm>
					<primary>functions</primary>
					<!--<secondary>handler functions</secondary>-->
					<secondary><command>gettimeofday_s()</command></secondary>
				</indexterm>
<!--				
				<indexterm>
					<primary>handler functions</primary>
					<secondary>Handlers</secondary>
					<tertiary><command>gettimeofday_s()</command></tertiary>
				</indexterm>
				-->
				<indexterm>
					<primary><command>gettimeofday_s()</command></primary>
					<secondary>functions</secondary>
<!-- 					<tertiary>handler functions</tertiary> -->
				</indexterm>
				
				<para>The number of seconds since UNIX epoch (January 1, 1970).</para>
			</listitem>	
		</varlistentry>
		
		<varlistentry>
			<term>ctime()</term>
			<listitem>
				<indexterm>
					<primary>functions</primary>
					<!--<secondary>handler functions</secondary>-->
					<secondary><command>ctime()</command></secondary>
				</indexterm>
<!--				
				<indexterm>
					<primary>handler functions</primary>
					<secondary>Handlers</secondary>
					<tertiary><command>ctime()</command></tertiary>
				</indexterm>
				-->
				<indexterm>
					<primary><command>ctime()</command></primary>
					<secondary>functions</secondary>
<!-- 					<tertiary>handler functions</tertiary> -->
				</indexterm>				
				<para>
					Convert number of seconds since UNIX epoch to date.
				</para>
			</listitem>	
		</varlistentry>
		
		<!--
		    <varlistentry>
			    <term>get_cycles()</term>
			    <listitem>
				    <para>A snapshot of the hardware cycle counter.</para>
			    </listitem>	
		    </varlistentry>
		    -->
		    
		    <varlistentry>
			    <term>pp()</term>
			    <listitem>
				    <indexterm>
					    <primary>functions</primary>
					    <!--<secondary>handler functions</secondary>-->
					    <secondary><command>pp()</command></secondary>
				    </indexterm>
<!--				    
				    <indexterm>
					    <primary>handler functions</primary>
					    <secondary>Handlers</secondary>
					    <tertiary><command>pp()</command></tertiary>
				    </indexterm>
				    -->
				    <indexterm>
					    <primary><command>pp()</command></primary>
					    <secondary>functions</secondary>
<!-- 					    <tertiary>handler functions</tertiary> -->
				    </indexterm>
				    <para>A string describing the probe point currently being handled.</para>
			    </listitem>	
		    </varlistentry>
		    <!-- removed, doesnt work as expected anymore
			 <varlistentry>
				 <term>probefunc()</term>
				 <listitem>
					 <para>If known, the name of the function in which the probe was placed.</para>
				 </listitem>	
			 </varlistentry>
			 -->
			 
			 <varlistentry>
				 <term>thread_indent()</term>
				 <listitem>
					 <indexterm>
						 <primary>functions</primary>
						 <!--<secondary>handler functions</secondary>-->
						 <secondary><command>thread_indent()</command></secondary>
					 </indexterm>
<!--					 
					 <indexterm>
						 <primary>handler functions</primary>
						 <secondary>Handlers</secondary>
						 <tertiary><command>thread_indent()</command></tertiary>
					 </indexterm>
					 -->
					 <indexterm>
						 <primary><command>thread_indent()</command></primary>
						 <secondary>functions</secondary>
<!-- 						 <tertiary>handler functions</tertiary> -->
					 </indexterm>
					 <para>
						 This particular function is quite useful, providing you with a way
						 to better organize your print results. The function takes one
						 argument, an indentation delta, which indicates how many
						 spaces to add or remove from a thread's "indentation counter".
						 It then returns a
						 string with some generic trace data along with an appropriate number
						 of indentation spaces.
					 </para>
					 
					 <para>
						 The generic data included in the returned string includes a
						 timestamp (number of microseconds since the 
						 first call to <command>thread_indent()</command> by the thread),
						 a process name, and the thread ID. This allows you to
						 identify what functions were called, who called them, and the
						 duration of each function call.
					 </para>	
					 
					 <para>
						 If call entries and exits immediately precede each other, it is easy
						 to match them. However, in most cases, after a first function call
						 entry is made several other call entries and exits may be made
						 before the first call exits. The indentation counter helps you match
						 an entry with its corresponding exit by indenting the next function
						 call if it is not the exit of the previous one.
					 </para>
					 
					 <para>
						 Consider the following example on the use of
						 <command>thread_indent()</command>:
					 </para>
					 
<example id="thread_indent"><title>thread_indent.stp</title>
<programlisting>
probe kernel.function("*@net/socket.c") 
{
  printf ("%s -> %s\n", thread_indent(1), probefunc())
}
probe kernel.function("*@net/socket.c").return 
{
  printf ("%s &lt;- %s\n", thread_indent(-1), probefunc())
}
</programlisting>
</example>
					 
					 <para>
						 <xref linkend="thread_indent"/> prints out the
						 <command>thread_indent()</command> and probe functions at each event
						 in the following format:</para>
					 
<screen>
0 ftp(7223): -&gt; sys_socketcall
1159 ftp(7223):  -&gt; sys_socket
2173 ftp(7223):   -&gt; __sock_create
2286 ftp(7223):    -&gt; sock_alloc_inode
2737 ftp(7223):    &lt;- sock_alloc_inode
3349 ftp(7223):    -&gt; sock_alloc
3389 ftp(7223):    &lt;- sock_alloc
3417 ftp(7223):   &lt;- __sock_create
4117 ftp(7223):   -&gt; sock_create
4160 ftp(7223):   &lt;- sock_create
4301 ftp(7223):   -&gt; sock_map_fd
4644 ftp(7223):    -&gt; sock_map_file
4699 ftp(7223):    &lt;- sock_map_file
4715 ftp(7223):   &lt;- sock_map_fd
4732 ftp(7223):  &lt;- sys_socket
4775 ftp(7223): &lt;- sys_socketcall
</screen>
					 
					 <para>This sample output contains the following information:</para>
					 
					 <itemizedlist>
						 <listitem><para>The time (in microseconds) since the initial <command>thread_ident()</command> call for the thread (included in the string from <command>thread_ident()</command>).</para></listitem>
						 
						 <listitem><para>The process name (and its corresponding ID) that made the function call (included in the string from <command>thread_ident()</command>).</para></listitem>
						 
						 <listitem><para>An arrow signifying whether the call was an entry (<computeroutput>&lt;-</computeroutput>) or an exit (<computeroutput>-></computeroutput>); the indentations help you match specific function call entries with their corresponding exits.</para></listitem>
						 
						 <listitem><para>The name of the function called by the process.</para></listitem>
					 </itemizedlist>	
					 
					 <remark>remember to add a reference later to "tapsets" from here, to clarify
						 that thread_indent is defined in tapsets as a special function of sorts</remark>
					 
				 </listitem>	
			 </varlistentry>
			 
			 <varlistentry>
				 <term>name</term>
				 <listitem>
<indexterm>
<primary>local variables</primary>
<secondary>name</secondary>
</indexterm>

<indexterm>
<primary>variables (local)</primary>
<secondary>name</secondary>
</indexterm>

<indexterm>
<primary>name</primary>
<secondary>local variables</secondary>
</indexterm>					 
<!--					 <indexterm>
						 <primary>functions</primary>
						 <secondary>handler functions</secondary>
						 <tertiary><command>name</command></tertiary>
					 </indexterm>
					 
					 <indexterm>
						 <primary>handler functions</primary>
						 <secondary>Handlers</secondary>
						 <tertiary><command>name</command></tertiary>
					 </indexterm>
					 
					 <indexterm>
						 <primary><command>name</command></primary>
						 <secondary>Handlers</secondary>
						 <tertiary>handler functions</tertiary>
					 </indexterm>-->
					 <para>Identifies the name of a specific system call. This variable can
						 only be used in probes that use the event
						 <command>syscall.<replaceable>system_call</replaceable></command>.
					 </para>
				 </listitem>	
			 </varlistentry>
			 
			 <varlistentry>
				 <term>target()</term>
				 <listitem>
					 
					 <indexterm>
						 <primary>functions</primary>
<!-- 						 <secondary>handler functions</secondary> -->
						 <secondary><command>target()</command></secondary>
					 </indexterm>
<!--					 
					 <indexterm>
						 <primary>handler functions</primary>
						 <secondary>Handlers</secondary>
						 <tertiary><command>target()</command></tertiary>
					 </indexterm>
					 -->
					 <indexterm>
						 <primary><command>target()</command></primary>
						 <secondary>functions</secondary>
<!-- 						 <tertiary>handler functions</tertiary> -->
					 </indexterm>
					 <para>
						 Used in conjunction with <command>stap
							 <replaceable>script</replaceable> -x <replaceable>process
								 ID</replaceable></command> or <command>stap
							 <replaceable>script</replaceable> -c
							 <replaceable>command</replaceable></command>. If you want to specify
						 a script to take an argument of a process ID or command, use
						 <command>target()</command> as the variable in the script to refer
						 to it. For example:
					 </para>
					 
<example id="targetexample">
<title>targetexample.stp</title>
<programlisting>
probe syscall.* {
  if (pid() == target())
    printf("%s/n", name)
}	
</programlisting>
</example>
					 
					 <para>
						 When <xref linkend="targetexample"/> is run with the argument
						 <command>-x <replaceable>process ID</replaceable></command>, it
						 watches all system calls (as specified by the event
						 <command>syscall.*</command>) and prints out the name of all system
						 calls made by the specified process.
					 </para>
					 
					 <para>
						 This has the same effect as specifying <command>if (pid() ==
							 <replaceable>process ID</replaceable>)</command> each time you wish
						 to target a specific process. However, using
						 <command>target()</command> makes it easier for you to re-use the
						 script, giving you the ability to simply pass a process ID as an
						 argument each time you wish to run the script (e.g. <command>stap
							 targetexample.stp -x <replaceable>process ID</replaceable></command>).
					 </para>
					 <!--		
							<note>
								<title>Note</title>
								<para>In <xref linkend="targetexample"/>, <command>name</command> instructs SystemTap to capture the name of the process</para>
							</note>	-->
							
						</listitem>
					</varlistentry>
					
					<!--	
						<varlistentry>
							<term></term>
							<listitem>
								<para></para>
							</listitem>	
						</varlistentry>
						-->	
					</variablelist>		
					
					<para>For more information about supported SystemTap functions, refer to
						<command>man stapfuncs</command>.
					</para>
					
					<remark>will need a complete listing of supported handler functions? also, SystemTap function descriptions seem ambiguous, please advise.</remark>
					
					<!--	
						<para>
							<replaceable>variable</replaceable> can be either <command>%s</command> for strings, or <command>%d</command> for numbers, depending on the <replaceable>handler function</replaceable> used. Each <command>printf ()</command> statement can contain multiple <replaceable>variable</replaceable>s, with each one corresponding to a matching <replaceable>handler function</replaceable>. Multiple <replaceable>handler function</replaceable>s are delimited by comma (<command>,</command>). 
						</para>	
						
						<command>printf ()</command> is a SystemTap-supported C statement, and can also trap data using a wide variety
						
						SystemTap supports a wide variety of handler functions that can trap data when triggered by events. One way to display these functions is to use the <command>print()</command>   
					</para>	
					
					
					<para>
						<xref linkend="wildcards"/> illustrates an example of a SystemTap script that contains no handlers. SystemTap will still be able to run the script, but no information will be displayed. 	
					</para>
					-->
					
  </section>
</section>