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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>4.2.4. I/O Monitoring (By Device)</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css" /><meta name="generator" content="publican 1.6" /><meta name="package" content="Systemtap-SystemTap_Beginners_Guide-1.0-en-US-2.0-2" /><link rel="home" href="index.html" title="SystemTap Beginners Guide" /><link rel="up" href="mainsect-disk.html" title="4.2. Disk" /><link rel="prev" href="traceiosect.html" title="4.2.3. Track Cumulative IO" /><link rel="next" href="inodewatchsect.html" title="4.2.5. Monitoring Reads and Writes to a File" /></head><body class=""><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site" /></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site" /></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="traceiosect.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="inodewatchsect.html"><strong>Next</strong></a></li></ul><div xml:lang="en-US" class="section" title="4.2.4. I/O Monitoring (By Device)" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="traceio2sect">4.2.4. I/O Monitoring (By Device)</h3></div></div></div><a id="id2873849" class="indexterm"></a><a id="id2834270" class="indexterm"></a><a id="id2905060" class="indexterm"></a><a id="id2871918" class="indexterm"></a><a id="id2800201" class="indexterm"></a><div class="para">
This section describes how to monitor I/O activity on a specific device.
</div><div class="formalpara"><h5 class="formalpara" id="traceio2">traceio2.stp</h5>
<pre class="programlisting">
#! /usr/bin/env stap
global device_of_interest
probe begin {
/* The following is not the most efficient way to do this.
One could directly put the result of usrdev2kerndev()
into device_of_interest. However, want to test out
the other device functions */
dev = usrdev2kerndev($1)
device_of_interest = MKDEV(MAJOR(dev), MINOR(dev))
}
probe vfs.write, vfs.read
{
if (dev == device_of_interest)
printf ("%s(%d) %s 0x%x\n",
execname(), pid(), probefunc(), dev)
}
</pre>
</div><a id="id2818575" class="indexterm"></a><a id="id2992782" class="indexterm"></a><a id="id3091452" class="indexterm"></a><a id="id2889768" class="indexterm"></a><a id="id2983284" class="indexterm"></a><a id="id4354532" class="indexterm"></a><div class="para">
<a class="xref" href="traceio2sect.html#traceio2" title="traceio2.stp">traceio2.stp</a> takes 1 argument: the whole device number. To get this number, use <code class="command">stat -c "0x%D" <em class="replaceable"><code>directory</code></em></code>, where <code class="command"><em class="replaceable"><code>directory</code></em></code> is located in the device you wish to monitor.
</div><a id="id4330879" class="indexterm"></a><a id="id2872221" class="indexterm"></a><a id="id2953637" class="indexterm"></a><div class="para">
The <code class="command">usrdev2kerndev()</code> function converts the whole device number into the format understood by the kernel. The output produced by <code class="command">usrdev2kerndev()</code> is used in conjunction with the <code class="command">MKDEV()</code>, <code class="command">MINOR()</code>, and <code class="command">MAJOR()</code> functions to determine the major and minor numbers of a specific device.
</div><div class="para">
The output of <a class="xref" href="traceio2sect.html#traceio2" title="traceio2.stp">traceio2.stp</a> includes the name and ID of any process performing a read/write, the function it is performing (i.e. <code class="command">vfs_read</code> or <code class="command">vfs_write</code>), and the kernel device number.
</div><div class="para">
The following example is an excerpt from the full output of <code class="command">stap traceio2.stp 0x805</code>, where <code class="literal">0x805</code> is the whole device number of <code class="filename">/home</code>. <code class="filename">/home</code> resides in <code class="filename">/dev/sda5</code>, which is the device we wish to monitor.
</div><div class="example" id="traceio2output"><div class="example-contents"><pre class="screen">
[...]
synergyc(3722) vfs_read 0x800005
synergyc(3722) vfs_read 0x800005
cupsd(2889) vfs_write 0x800005
cupsd(2889) vfs_write 0x800005
cupsd(2889) vfs_write 0x800005
[...]
</pre></div><h6>Example 4.9. <a class="xref" href="traceio2sect.html#traceio2" title="traceio2.stp">traceio2.stp</a> Sample Output</h6></div><br class="example-break" /></div><ul class="docnav"><li class="previous"><a accesskey="p" href="traceiosect.html"><strong>Prev</strong>4.2.3. Track Cumulative IO</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="inodewatchsect.html"><strong>Next</strong>4.2.5. Monitoring Reads and Writes to a File</a></li></ul></body></html>
