docs: Convert 'internals' to RST and move it to 'kbase/internal/overview.rst'

Note that this document was not referenced from any top level page. This
patch does a straight conversion and leaves it unreferenced.

Next patch will then modify it to serve as an overview (hence the new
name) of how an API call happens.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

docs/kbase/internals/meson.build

@@ -4,6 +4,7 @@ docs_kbase_internals_files = [
   'incremental-backup',
   'locking',
   'migration',
+  'overview',
   'rpc',
 ]
 

docs/kbase/internals/overview.rst

@@ -0,0 +1,117 @@
+==========================
+libvirt internals overview
+==========================
+
+This section provides documents useful to those working on the libvirt
+internals, adding new public APIs, new hypervisor drivers or extending the
+libvirtd daemon code.
+
+-  Introduction to basic rules and guidelines for `hacking <../../hacking.html>`__ on
+   libvirt code
+-  Guide to adding `public APIs <../../api_extension.html>`__
+-  Insight into libvirt `event loop and worker
+   pool <eventloop.html>`__
+-  Approach for `spawning commands <command.html>`__ from libvirt
+   driver code
+-  The libvirt `RPC infrastructure <rpc.html>`__
+-  The `Resource Lock Manager <locking.html>`__
+
+Before adding new code it will be important to get a basic understanding of the
+many elements involved with making any call or change to the libvirt code. The
+architecture `goals <../../goals.html>`__ must be adhered to when submitting new code.
+Understanding the many places that need to be touched and the interactions
+between various subsystems within libvirt will directly correlate to the ability
+to be successful in getting new code accepted.
+
+The following diagram depicts code flow from a client application, in this case
+the libvirt provided ``virsh`` command through the various layers to elicit a
+response from some chosen hypervisor.
+
+.. image:: ../../images/libvirt-virConnect-example.png
+   :alt: virConnectOpen calling sequence
+
+-  "virsh -c qemu:///system list --all"
+
+   After the virsh code processes the input arguments, it eventually will make a
+   call to open the connection using a default set of authentication credentials
+   (virConnectAuthDefault).
+
+-  virConnectOpenAuth()
+
+   Each of the virConnectOpen APIs will first call virInitialize() and then
+   revector through the local "do_open():" call.
+
+   -  virInitialize()
+
+      Calls the registration API for each of the drivers with client-side only
+      capabilities and then call the remoteRegister() API last. This ensures the
+      virDriverTab[] tries local drivers first before using the remote driver.
+
+   -  Loop through virDriverTab[] entries trying to call their respective "open"
+      entry point (in our case remoteOpen())
+
+   -  After successful return from the virDriverTab[] open() API, attempt to
+      find and open other drivers (network, interface, storage, etc.)
+
+-  remoteOpen()
+
+   After a couple of URI checks, a call to doRemoteOpen() is made
+
+   -  Determine network transport and host/port to use from URI
+
+      The transport will be either tls, unix, ssh, libssh2, ext, or tcp with the
+      default of tls. Decode the host/port if provided or default to
+      "localhost".
+
+   -  virNetClientRegisterAsyncIO()
+
+      Register an I/O callback mechanism to get returned data via
+      virNetClientIncomingEvent()
+
+   -  "call(...REMOTE_PROC_OPEN...)"
+
+      Eventually routes into virNetClientProgramCall() which will call
+      virNetClientSendWithReply() and eventually uses virNetClientIO()to send
+      the message to libvirtd and then waits for a response using
+      virNetClientIOEventLoop()
+
+   -  virNetClientIncomingEvent()
+
+      Receives the returned packet and processes through
+      virNetClientIOUpdateCallback()
+
+-  libvirtd Daemon
+
+   -  Daemon Startup
+
+      The daemon initialization processing will declare itself as a daemon via a
+      virNetDaemonNew() call, then creates new server using virNetServerNew()
+      and adds that server to the main daemon struct with
+      virNetDaemonAddServer() call. It will then use virDriverLoadModule() to
+      find/load all known drivers, set up an RPC server program using the
+      ``remoteProcs[]`` table via a virNetServerProgramNew() call. The table is
+      the corollary to the ``remote_procedure`` enum list in the client. It
+      lists all the functions to be called in the same order. Once RPC is set
+      up, networking server sockets are opened, the various driver state
+      initialization routines are run from the ``virStateDriverTab[]``, the
+      network links are enabled, and the daemon waits for work.
+
+   -  RPC
+
+      When a message is received, the ``remoteProcs[]`` table is referenced for
+      the 'REMOTE_PROC_OPEN' call entry. This results in remoteDispatchOpen()
+      being called via the virNetServerProgramDispatchCall().
+
+   -  remoteDispatchOpen()
+
+      The API will read the argument passed picking out the ``name`` of the
+      driver to be opened. The code will then call virConnectOpen() or
+      virConnectOpenReadOnly() depending on the argument ``flags``.
+
+   -  virConnectOpen() or virConnectOpenReadOnly()
+
+      Just like the client except that upon entry the URI is what was passed
+      from the client and will be found and opened to process the data.
+
+      The returned structure data is returned via the virNetServer interfaces to
+      the remote driver which then returns it to the client application.