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120 lines
6.0 KiB
XML
120 lines
6.0 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html>
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<html xmlns="http://www.w3.org/1999/xhtml">
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<body>
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<h1>libvirt internals</h1>
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<p>
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This section provides documents useful to those working on the libvirt
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internals, adding new public APIs, new hypervisor drivers or extending
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the libvirtd daemon code.
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</p>
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<ul>
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<li>Introduction to basic rules and guidelines for
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<a href="hacking.html">hacking</a> on libvirt code</li>
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<li>Guide to adding <a href="api_extension.html">public APIs</a></li>
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<li>Insight into libvirt <a href="internals/eventloop.html">event loop and worker pool</a></li>
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<li>Approach for <a href="internals/command.html">spawning commands</a>
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from libvirt driver code</li>
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<li>The libvirt <a href="internals/rpc.html">RPC infrastructure</a></li>
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<li>The <a href="internals/locking.html">Resource Lock Manager</a></li>
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</ul>
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<p>Before adding new code it will be important to get a basic understanding
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of the many elements involved with making any call or change to the libvirt
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code. The architecture <a href="goals.html">goals</a> must be adhered to
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when submitting new code. Understanding the many places that need to be
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touched and the interactions between various subsystems within libvirt
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will directly correlate to the ability to be successful in getting new
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code accepted.</p>
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<p>The following diagram depicts code flow from a client application, in
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this case the libvirt provided <code>virsh</code> command through the
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various layers to elicit a response from some chosen hypervisor.
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</p>
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<p class="image">
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<img alt="virConnectOpen calling sequence"
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src="libvirt-virConnect-example.png"/>
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</p>
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<ul>
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<li>"virsh -c qemu:///system list --all"
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<p>After the virsh code processes the input arguments, it eventually
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will make a call to open the connection using a default set of
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authentication credentials (virConnectAuthDefault). </p></li>
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<li>virConnectOpenAuth()
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<p>Each of the virConnectOpen APIs will first call virInitialize() and
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then revector through the local "do_open():" call.</p>
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<ul>
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<li>virInitialize()
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<p>Calls the registration API for each of the drivers with
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client-side only capabilities and then call the remoteRegister()
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API last. This ensures the virDriverTab[] tries local drivers
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first before using the remote driver.</p></li>
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<li>Loop through virDriverTab[] entries trying to call their
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respective "open" entry point (in our case remoteOpen())</li>
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<li>After successful return from the virDriverTab[] open()
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API, attempt to find and open other drivers (network, interface,
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storage, etc.)</li>
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</ul>
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</li>
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<li>remoteOpen()
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<p>After a couple of URI checks, a call to doRemoteOpen() is made</p>
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<ul>
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<li>Determine network transport and host/port to use from URI
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<p>The transport will be either tls, unix, ssh, libssh2, ext,
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or tcp with the default of tls. Decode the host/port if provided
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or default to "localhost".</p></li>
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<li>virNetClientRegisterAsyncIO()
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<p>Register an I/O callback mechanism to get returned data via
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virNetClientIncomingEvent()</p></li>
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<li>"call(...REMOTE_PROC_OPEN...)"
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<p>Eventually routes into virNetClientProgramCall() which will
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call virNetClientSendWithReply() and eventually uses
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virNetClientIO()to send the message to libvirtd and
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then waits for a response using virNetClientIOEventLoop()</p></li>
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<li>virNetClientIncomingEvent()
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<p>Receives the returned packet and processes through
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virNetClientIOUpdateCallback()</p></li>
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</ul>
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</li>
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<li>libvirtd Daemon
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<p></p>
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<ul>
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<li>Daemon Startup
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<p>The daemon initialization processing will declare itself
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as a daemon via a virNetDaemonNew() call, then creates new server
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using virNetServerNew() and adds that server to the main daemon
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struct with virNetDaemonAddServer() call. It will then use
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virDriverLoadModule() to find/load all known drivers,
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set up an RPC server program using the <code>remoteProcs[]</code>
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table via a virNetServerProgramNew() call. The table is the
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corollary to the <code>remote_procedure</code> enum list in
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the client. It lists all the functions to be called in
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the same order. Once RPC is set up, networking server sockets
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are opened, the various driver state initialization routines
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are run from the <code>virStateDriverTab[]</code>, the network
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links are enabled, and the daemon waits for work.</p></li>
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<li>RPC
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<p>When a message is received, the <code>remoteProcs[]</code>
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table is referenced for the 'REMOTE_PROC_OPEN' call entry.
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This results in remoteDispatchOpen() being called via the
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virNetServerProgramDispatchCall().</p></li>
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<li>remoteDispatchOpen()
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<p>The API will read the argument passed picking out the
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<code>name</code> of the driver to be opened. The code
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will then call virConnectOpen() or virConnectOpenReadOnly()
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depending on the argument <code>flags</code>.</p></li>
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<li>virConnectOpen() or virConnectOpenReadOnly()
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<p>Just like the client except that upon entry the URI
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is what was passed from the client and will be found
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and opened to process the data.</p>
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<p>The returned structure data is returned via the
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virNetServer interfaces to the remote driver which then
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returns it to the client application.</p></li>
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</ul>
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</li>
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</ul>
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</body>
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</html>
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