mirror of
https://gitlab.com/libvirt/libvirt.git
synced 2024-12-28 11:21:44 +03:00
139 lines
8.3 KiB
HTML
139 lines
8.3 KiB
HTML
<?xml version="1.0" encoding="ISO-8859-1"?>
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
|
|
<html xmlns="http://www.w3.org/1999/xhtml">
|
|
<!--
|
|
This file is autogenerated from errors.html.in
|
|
Do not edit this file. Changes will be lost.
|
|
-->
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
|
|
<link rel="stylesheet" type="text/css" href="main.css" />
|
|
<link rel="SHORTCUT ICON" href="32favicon.png" />
|
|
<title>libvirt: Handling of errors</title>
|
|
<meta name="description" content="libvirt, virtualization, virtualization API" />
|
|
</head>
|
|
<body>
|
|
<div id="header">
|
|
<div id="headerLogo"></div>
|
|
<div id="headerSearch">
|
|
<form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><div>
|
|
<input id="query" name="query" type="text" size="12" value="" />
|
|
<input id="submit" name="submit" type="submit" value="Search" />
|
|
</div></form>
|
|
</div>
|
|
</div>
|
|
<div id="body">
|
|
<div id="menu">
|
|
<ul class="l0"><li>
|
|
<div>
|
|
<a title="Front page of the libvirt website" class="inactive" href="index.html">Home</a>
|
|
</div>
|
|
</li><li>
|
|
<div>
|
|
<a title="Details of new features and bugs fixed in each release" class="inactive" href="news.html">News</a>
|
|
</div>
|
|
</li><li>
|
|
<div>
|
|
<a title="Get the latest source releases, binary builds and get access to the source repository" class="inactive" href="downloads.html">Downloads</a>
|
|
</div>
|
|
</li><li>
|
|
<div>
|
|
<a title="Information for users, administrators and developers" class="inactive" href="docs.html">Documentation</a>
|
|
</div>
|
|
</li><li>
|
|
<div>
|
|
<a title="User contributed content" class="inactive" href="http://wiki.libvirt.org">Wiki</a>
|
|
</div>
|
|
</li><li>
|
|
<div>
|
|
<a title="Frequently asked questions" class="inactive" href="FAQ.html">FAQ</a>
|
|
</div>
|
|
</li><li>
|
|
<div>
|
|
<a title="How and where to report bugs and request features" class="inactive" href="bugs.html">Bug reports</a>
|
|
</div>
|
|
</li><li>
|
|
<div>
|
|
<a title="How to contact the developers via email and IRC" class="inactive" href="contact.html">Contact</a>
|
|
</div>
|
|
</li><li>
|
|
<div>
|
|
<a title="Miscellaneous links of interest related to libvirt" class="inactive" href="relatedlinks.html">Related Links</a>
|
|
</div>
|
|
</li><li>
|
|
<div>
|
|
<a title="Overview of all content on the website" class="inactive" href="sitemap.html">Sitemap</a>
|
|
</div>
|
|
</li></ul>
|
|
</div>
|
|
<div id="content">
|
|
<h1>Handling of errors</h1>
|
|
<p>The main goals of libvirt when it comes to error handling are:</p>
|
|
<ul><li>provide as much detail as possible</li><li>provide the information as soon as possible</li><li>dont force the library user into one style of error handling</li></ul>
|
|
<p>As result the library provide both synchronous, callback based and
|
|
asynchronous error reporting. When an error happens in the library code the
|
|
error is logged, allowing to retrieve it later and if the user registered an
|
|
error callback it will be called synchronously. Once the call to libvirt ends
|
|
the error can be detected by the return value and the full information for
|
|
the last logged error can be retrieved.</p>
|
|
<p>To avoid as much as possible troubles with a global variable in a
|
|
multithreaded environment, libvirt will associate when possible the errors to
|
|
the current connection they are related to, that way the error is stored in a
|
|
dynamic structure which can be made thread specific. Error callback can be
|
|
set specifically to a connection with</p>
|
|
<p>So error handling in the code is the following:</p>
|
|
<ol><li>if the error can be associated to a connection for example when failing
|
|
to look up a domain
|
|
<ol><li>if there is a callback associated to the connection set with <a href="html/libvirt-virterror.html#virConnSetErrorFunc">virConnSetErrorFunc</a>,
|
|
call it with the error information</li><li>otherwise if there is a global callback set with <a href="html/libvirt-virterror.html#virSetErrorFunc">virSetErrorFunc</a>,
|
|
call it with the error information</li><li>otherwise call <a href="html/libvirt-virterror.html#virDefaultErrorFunc">virDefaultErrorFunc</a>
|
|
which is the default error function of the library issuing the error
|
|
on stderr</li><li>save the error in the connection for later retrieval with <a href="html/libvirt-virterror.html#virConnGetLastError">virConnGetLastError</a></li></ol></li><li>otherwise like when failing to create an hypervisor connection:
|
|
<ol><li>if there is a global callback set with <a href="html/libvirt-virterror.html#virSetErrorFunc">virSetErrorFunc</a>,
|
|
call it with the error information</li><li>otherwise call <a href="html/libvirt-virterror.html#virDefaultErrorFunc">virDefaultErrorFunc</a>
|
|
which is the default error function of the library issuing the error
|
|
on stderr</li><li>save the error in the connection for later retrieval with <a href="html/libvirt-virterror.html#virGetLastError">virGetLastError</a></li></ol></li></ol>
|
|
<p>In all cases the error information is provided as a <a href="html/libvirt-virterror.html#virErrorPtr">virErrorPtr</a> pointer to
|
|
read-only structure <a href="html/libvirt-virterror.html#virError">virError</a> containing the
|
|
following fields:</p>
|
|
<ul><li>code: an error number from the <a href="html/libvirt-virterror.html#virErrorNumber">virErrorNumber</a>
|
|
enum</li><li>domain: an enum indicating which part of libvirt raised the error see
|
|
<a href="html/libvirt-virterror.html#virErrorDomain">virErrorDomain</a></li><li>level: the error level, usually VIR_ERR_ERROR, though there is room for
|
|
warnings like VIR_ERR_WARNING</li><li>message: the full human-readable formatted string of the error</li><li>conn: if available a pointer to the <a href="html/libvirt-libvirt.html#virConnectPtr">virConnectPtr</a>
|
|
connection to the hypervisor where this happened</li><li>dom: if available a pointer to the <a href="html/libvirt-libvirt.html#virDomainPtr">virDomainPtr</a> domain
|
|
targeted in the operation</li></ul>
|
|
<p>and then extra raw information about the error which may be initialized
|
|
to 0 or NULL if unused</p>
|
|
<ul><li>str1, str2, str3: string information, usually str1 is the error
|
|
message format</li><li>int1, int2: integer information</li></ul>
|
|
<p>So usually, setting up specific error handling with libvirt consist of
|
|
registering an handler with with <a href="html/libvirt-virterror.html#virSetErrorFunc">virSetErrorFunc</a> or
|
|
with <a href="html/libvirt-virterror.html#virConnSetErrorFunc">virConnSetErrorFunc</a>,
|
|
check the value of the code value, take appropriate action, if needed let
|
|
libvirt print the error on stderr by calling <a href="html/libvirt-virterror.html#virDefaultErrorFunc">virDefaultErrorFunc</a>.
|
|
For asynchronous error handing, set such a function doing nothing to avoid
|
|
the error being reported on stderr, and call virConnGetLastError or
|
|
virGetLastError when an API call returned an error value. It can be a good
|
|
idea to use <a href="html/libvirt-virterror.html#virResetLastError">virResetError</a> or <a href="html/libvirt-virterror.html#virConnResetLastError">virConnResetLastError</a>
|
|
once an error has been processed fully.</p>
|
|
<p>At the python level, there only a global reporting callback function at
|
|
this point, see the error.py example about it:</p>
|
|
<pre>def handler(ctxt, err):
|
|
global errno
|
|
|
|
#print "handler(%s, %s)" % (ctxt, err)
|
|
errno = err
|
|
|
|
libvirt.registerErrorHandler(handler, 'context') </pre>
|
|
<p>the second argument to the registerErrorHandler function is passed as the
|
|
first argument of the callback like in the C version. The error is a tuple
|
|
containing the same field as a virError in C, but cast to Python.</p>
|
|
</div>
|
|
</div>
|
|
<div id="footer">
|
|
<p id="sponsor">
|
|
Sponsored by:<br /><a href="http://et.redhat.com/"><img src="et.png" alt="Project sponsored by Red Hat Emerging Technology" /></a></p>
|
|
</div>
|
|
</body>
|
|
</html>
|