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<htmlxmlns="http://www.w3.org/1999/xhtml"><head><metahttp-equiv="Content-Type"content="text/html; charset=ISO-8859-1"/><linkrel="stylesheet"type="text/css"href="libvirt.css"/><linkrel="SHORTCUT ICON"href="/32favicon.png"/><title>Handling of errors</title></head><body><divid="container"><divid="intro"><divid="adjustments"></div><divid="pageHeader"></div><divid="content2"><h1class="style1">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 informations 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
andasynchronous error reporting. When an error happens in the library code
theerror is logged, allowing to retrieve it later and if the user registered
anerror callback it will be called synchronously. Once the call to libvirt
endsthe error can be detected by the return value and the full information
forthe last logged error can be retrieved.</p><p>To avoid as much as prossible troubles with a global variable in
amultithreaded environment, libvirt will associate when possible the errors
tothe current connection they are related to, that way the error is stored in
adynamic structure which can be made thread specific. Error callback can
beset 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
failingto look up a domain
<ol><li>if there is a callback associated to the connection set with <ahref="html/libvirt-virterror.html#virConnSetErrorFunc">virConnSetErrorFunc</a>,call
it with the error informations</li>
<li>otherwise if there is a global callback set with <ahref="html/libvirt-virterror.html#virSetErrorFunc">virSetErrorFunc</a>,call
the value of the code value, take appropriate action, if needed letlibvirt
print the error on stderr by calling <ahref="html/libvirt-virterror.html#virDefaultErrorFunc">virDefaultErrorFunc</a>.For
asynchronous error handing, set such a function doing nothing to avoidthe
error being reported on stderr, and call virConnGetLastError
orvirGetLastError when an API call returned an error value. It can be a
goodidea to use <ahref="html/libvirt-virterror.html#virResetLastError">virResetError</a>or <ahref="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
atthis point, see the error.py example about it:</p><pre>def handler(ctxt, err):
tuplecontaining the same field as a virError in C, but cast to Python.</p></div></div><divclass="linkList2"><divclass="llinks2"><h3class="links2"><span>main menu</span></h3><ul><li><ahref="index.html">Home</a></li><li><ahref="news.html">Releases</a></li><li><ahref="intro.html">Introduction</a></li><li><ahref="architecture.html">libvirt architecture</a></li><li><ahref="downloads.html">Downloads</a></li><li><ahref="format.html">XML Formats</a></li><li><ahref="python.html">Binding for Python</a></li><li><ahref="errors.html">Handling of errors</a></li><li><ahref="FAQ.html">FAQ</a></li><li><ahref="bugs.html">Reporting bugs and getting help</a></li><li><ahref="html/index.html">API Menu</a></li><li><ahref="examples/index.html">C code examples</a></li><li><ahref="ChangeLog.html">Recent Changes</a></li></ul></div><divclass="llinks2"><h3class="links2"><span>related links</span></h3><ul><li><ahref="https://www.redhat.com/archives/libvir-list/">Mail archive</a></li><li><ahref="https://bugzilla.redhat.com/bugzilla/buglist.cgi?product=Fedora+Core&component=libvirt&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&bug_status=MODIFIED&short_desc_type=allwordssubstr&short_desc=&long_desc_type=allwordssubstr">Open bugs</a></li><li><ahref="http://virt-manager.et.redhat.com/">virt-manager</a></li><li><ahref="http://search.cpan.org/~danberr/Sys-Virt-0.1.0/">Perl bindings</a></li><li><ahref="http://www.cl.cam.ac.uk/Research/SRG/netos/xen/index.html">Xen project</a></li><li><formaction="search.php"enctype="application/x-www-form-urlencoded"method="get"><inputname="query"type="text"size="12"value="Search..."/><inputname="submit"type="submit"value="Go"/></form></li><li><ahref="http://xmlsoft.org/"><imgsrc="Libxml2-Logo-90x34.gif"alt="Made with Libxml2 Logo"/></a></li></ul><pclass="credits">Graphics and design by <ahref="mail:dfong@redhat.com">Diana Fong</a></p></div></div><divid="bottom"><pclass="p1"></p></div></div></body></html>
