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docs: html.in: Convert api_extension to rst
Signed-off-by: Erik Skultety <eskultet@redhat.com> Reviewed-by: Peter Krempa <pkrempa@redhat.com>
This commit is contained in:
Erik Skultety
parent
d91482807e
commit
9d503ea9dc
@ -1,376 +0,0 @@
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<?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>Implementing a new API in Libvirt</h1>
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<ul id="toc"></ul>
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<p>
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This document walks you through the process of implementing a new
|
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API in libvirt. Remember that new API consists of any new public
|
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functions, as well as the addition of flags or extensions of XML used by
|
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existing functions.
|
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</p>
|
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|
||||
<p>
|
||||
Before you begin coding, it is critical that you propose your
|
||||
changes on the libvirt mailing list and get feedback on your ideas to
|
||||
make sure what you're proposing fits with the general direction of the
|
||||
project. Even before doing a proof of concept implementation, send an
|
||||
email giving an overview of the functionality you think should be
|
||||
added to libvirt. Someone may already be working on the feature you
|
||||
want. Also, recognize that everything you write is likely to undergo
|
||||
significant rework as you discuss it with the other developers, so
|
||||
don't wait too long before getting feedback.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Adding a new API to libvirt is not difficult, but there are quite a
|
||||
few steps. This document assumes that you are familiar with C
|
||||
programming and have checked out the libvirt code from the source code
|
||||
repository and successfully built the existing tree. Instructions on
|
||||
how to check out and build the code can be found at:
|
||||
</p>
|
||||
|
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<p>
|
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<a href="https://libvirt.org/downloads.html">https://libvirt.org/downloads.html</a>
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</p>
|
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|
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<p>
|
||||
Once you have a working development environment, the steps to create a
|
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new API are:
|
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</p>
|
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<ol>
|
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<li>define the public API</li>
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<li>define the internal driver API</li>
|
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<li>implement the public API</li>
|
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<li>implement the remote protocol:
|
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<ol>
|
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<li>define the wire protocol format</li>
|
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<li>implement the RPC client</li>
|
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<li>implement the server side dispatcher</li>
|
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</ol>
|
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</li>
|
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<li>use new API where appropriate in drivers</li>
|
||||
<li>add virsh support</li>
|
||||
<li>add common handling for new API</li>
|
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<li>for each driver that can support the new API:
|
||||
<ol>
|
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<li>add prerequisite support</li>
|
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<li>fully implement new API</li>
|
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</ol>
|
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</li>
|
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</ol>
|
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|
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<p>
|
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It is, of course, possible to implement the pieces in any order, but
|
||||
if the development tasks are completed in the order listed, the code
|
||||
will compile after each step. Given the number of changes required,
|
||||
verification after each step is highly recommended.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Submit new code in the form of one patch per step. That's not to say
|
||||
submit patches before you have working functionality--get the whole thing
|
||||
working and make sure you're happy with it. Then use git to break the
|
||||
changes into pieces so you don't drop a big blob of code on the
|
||||
mailing list in one go. Also, you should follow the upstream tree, and
|
||||
rebase your series to adapt your patches to work with any other changes
|
||||
that were accepted upstream during your development.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Don't mix anything else into the patches you submit. The patches
|
||||
should be the minimal changes required to implement the functionality
|
||||
you're adding. If you notice a bug in unrelated code (i.e., code you
|
||||
don't have to touch to implement your API change) during development,
|
||||
create a patch that just addresses that bug and submit it
|
||||
separately.
|
||||
</p>
|
||||
|
||||
<h2><a id='publicapi'>Defining the public API</a></h2>
|
||||
|
||||
<p>The first task is to define the public API. If the new API
|
||||
involves an XML extension, you have to enhance the RelaxNG
|
||||
schema and document the new elements or attributes:</p>
|
||||
|
||||
<p><code>
|
||||
docs/schemas/domaincommon.rng<br/>
|
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docs/formatdomain.html.in
|
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</code></p>
|
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|
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<p>If the API extension involves a new function, you have to add a
|
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declaration in the public header, and arrange to export the
|
||||
function name (symbol) so other programs can link against the
|
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libvirt library and call the new function:</p>
|
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|
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<p><code>
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include/libvirt/libvirt-$MODULE.h.in
|
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src/libvirt_public.syms
|
||||
</code></p>
|
||||
|
||||
<p>
|
||||
Please consult our
|
||||
<a href="coding-style.html#xml-element-and-attribute-naming">coding style</a>
|
||||
guide on elements and attribute names.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
This task is in many ways the most important to get right, since once
|
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the API has been committed to the repository, it's libvirt's policy
|
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never to change it. Mistakes in the implementation are bugs that you
|
||||
can fix. Make a mistake in the API definition and you're stuck with
|
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it, so think carefully about the interface and don't be afraid to
|
||||
rework it as you go through the process of implementing it.
|
||||
</p>
|
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|
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<h2><a id='internalapi'>Defining the internal API</a></h2>
|
||||
|
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<p>
|
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Each public API call is associated with a driver, such as a host
|
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virtualization driver, a network virtualization driver, a storage
|
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virtualization driver, a state driver, or a device monitor. Adding
|
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the internal API is ordinarily a matter of adding a new member to the
|
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struct representing one of these drivers.
|
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</p>
|
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|
||||
<p>
|
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Of course, it's possible that the new API will involve the creation of
|
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an entirely new driver type, in which case the changes will include the
|
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creation of a new struct type to represent the new driver type.
|
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</p>
|
||||
|
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<p>The driver structs are defined in:</p>
|
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|
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<p><code>src/driver-$MODULE.h</code></p>
|
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|
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<p>
|
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To define the internal API, first typedef the driver function
|
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prototype and then add a new field for it to the relevant driver
|
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struct. Then, update all existing instances of the driver to
|
||||
provide a <code>NULL</code> stub for the new function.
|
||||
</p>
|
||||
|
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<h2><a id='implpublic'>Implementing the public API</a></h2>
|
||||
|
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<p>
|
||||
Implementing the public API is largely a formality in which we wire up
|
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public API to the internal driver API. The public API implementation
|
||||
takes care of some basic validity checks before passing control to the
|
||||
driver implementation. In RFC 2119 vocabulary, this function:
|
||||
</p>
|
||||
|
||||
<ol class="ordinarylist">
|
||||
<li>SHOULD log a message with VIR_DEBUG() indicating that it is
|
||||
being called and its parameters;</li>
|
||||
<li>MUST call virResetLastError();</li>
|
||||
<li>SHOULD confirm that the connection is valid with
|
||||
virCheckConnectReturn() or virCheckConnectGoto();</li>
|
||||
<li><strong>SECURITY: If the API requires a connection with write
|
||||
privileges, MUST confirm that the connection flags do not
|
||||
indicate that the connection is read-only with
|
||||
virCheckReadOnlyGoto();</strong></li>
|
||||
<li>SHOULD do basic validation of the parameters that are being
|
||||
passed in, using helpers like virCheckNonNullArgGoto();</li>
|
||||
<li>MUST confirm that the driver for this connection exists and that
|
||||
it implements this function;</li>
|
||||
<li>MUST call the internal API;</li>
|
||||
<li>SHOULD log a message with VIR_DEBUG() indicating that it is
|
||||
returning, its return value, and status.</li>
|
||||
<li>MUST return status to the caller.</li>
|
||||
</ol>
|
||||
|
||||
<p>The public API calls are implemented in:</p>
|
||||
|
||||
<p><code>src/libvirt-$MODULE.c</code></p>
|
||||
|
||||
<h2><a id='remoteproto'>Implementing the remote protocol</a></h2>
|
||||
|
||||
<p>
|
||||
Implementing the remote protocol is essentially a
|
||||
straightforward exercise which is probably most easily
|
||||
understood by referring to the existing code.
|
||||
</p>
|
||||
|
||||
<h3><a id='wireproto'>Defining the wire protocol format</a></h3>
|
||||
|
||||
<p>
|
||||
Defining the wire protocol involves making additions to:
|
||||
</p>
|
||||
|
||||
<p><code>src/remote/remote_protocol.x</code></p>
|
||||
|
||||
<p>
|
||||
First, create two new structs for each new function that you're adding
|
||||
to the API. One struct describes the parameters to be passed to the
|
||||
remote function, and a second struct describes the value returned by
|
||||
the remote function. The one exception to this rule is that functions
|
||||
that return only 0 or -1 for status do not require a struct for returned
|
||||
data.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Second, add values to the remote_procedure enum for each new function
|
||||
added to the API.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Once these changes are in place, it's necessary to run 'make rpcgen'
|
||||
in the src directory to create the .c and .h files required by the
|
||||
remote protocol code. This must be done on a Linux host using the
|
||||
GLibC rpcgen program. Other rpcgen versions may generate code which
|
||||
results in bogus compile time warnings. This regenerates the
|
||||
following files:
|
||||
</p>
|
||||
|
||||
<p><code>
|
||||
src/remote/remote_daemon_dispatch_stubs.h
|
||||
src/remote/remote_daemon_dispatch.h
|
||||
src/remote/remote_daemon_dispatch.c
|
||||
src/remote/remote_protocol.c
|
||||
src/remote/remote_protocol.h
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||||
</code></p>
|
||||
|
||||
<h3><a id='rpcclient'>Implement the RPC client</a></h3>
|
||||
|
||||
<p>
|
||||
Implementing the RPC client uses the rpcgen generated .h files.
|
||||
The remote method calls go in:
|
||||
</p>
|
||||
|
||||
<p><code>src/remote/remote_driver.c</code></p>
|
||||
|
||||
<p>Each remote method invocation does the following:</p>
|
||||
|
||||
<ol class="ordinarylist">
|
||||
<li>locks the remote driver;</li>
|
||||
<li>sets up the method arguments;</li>
|
||||
<li>invokes the remote function;</li>
|
||||
<li>checks the return value, if necessary;</li>
|
||||
<li>extracts any returned data;</li>
|
||||
<li>frees any returned data;</li>
|
||||
<li>unlocks the remote driver.</li>
|
||||
</ol>
|
||||
|
||||
<h3><a id="serverdispatch">Implement the server side dispatcher</a></h3>
|
||||
|
||||
<p>
|
||||
Implementing the server side of the remote function call is simply a
|
||||
matter of deserializing the parameters passed in from the remote
|
||||
caller and passing them to the corresponding internal API function.
|
||||
The server side dispatchers are implemented in:
|
||||
</p>
|
||||
|
||||
<p><code>src/remote/remote_daemon_dispatch.c</code></p>
|
||||
|
||||
<p>Again, this step uses the .h files generated by make rpcgen.</p>
|
||||
|
||||
<p>
|
||||
After all three pieces of the remote protocol are complete, and
|
||||
the generated files have been updated, it will be necessary to
|
||||
update the file:</p>
|
||||
|
||||
<p><code>src/remote_protocol-structs</code></p>
|
||||
|
||||
<p>
|
||||
This file should only have new lines added; modifications to
|
||||
existing lines probably imply a backwards-incompatible API change.
|
||||
</p>
|
||||
|
||||
<h2><a id="internaluseapi">Use the new API internally</a></h2>
|
||||
|
||||
<p>
|
||||
Sometimes, a new API serves as a superset of existing API, by
|
||||
adding more granularity in what can be managed. When this is
|
||||
the case, it makes sense to share a common implementation by
|
||||
making the older API become a trivial wrapper around the new
|
||||
API, rather than duplicating the common code. This step should
|
||||
not introduce any semantic differences for the old API, and is
|
||||
not necessary if the new API has no relation to existing API.
|
||||
</p>
|
||||
|
||||
<h2><a id="virshuseapi">Expose the new API in virsh</a></h2>
|
||||
|
||||
<p>
|
||||
All new API should be manageable from the virsh command line
|
||||
shell. This proves that the API is sufficient for the intended
|
||||
purpose, and helps to identify whether the proposed API needs
|
||||
slight changes for easier usage. However, remember that virsh
|
||||
is used to connect to hosts running older versions of libvirtd,
|
||||
so new commands should have fallbacks to an older API if
|
||||
possible; implementing the virsh hooks at this point makes it
|
||||
very easy to test these fallbacks. Also remember to document
|
||||
virsh additions.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
A virsh command is composed of a few pieces of code. You need to
|
||||
define an array of vshCmdInfo structs for each new command that
|
||||
contain the help text and the command description text. You also need
|
||||
an array of vshCmdOptDef structs to describe the command options.
|
||||
Once you have those pieces in place you can write the function
|
||||
implementing the virsh command. Finally, you need to add the new
|
||||
command to the commands[] array. The following files need changes:
|
||||
</p>
|
||||
|
||||
<p><code>
|
||||
tools/virsh-$MODULE.c<br/>
|
||||
tools/virsh.pod
|
||||
</code></p>
|
||||
|
||||
<h2><a id="driverimpl">Implement the driver methods</a></h2>
|
||||
|
||||
<p>
|
||||
So, after all that, we get to the fun part. All functionality in
|
||||
libvirt is implemented inside a driver. Thus, here is where you
|
||||
implement whatever functionality you're adding to libvirt. You'll
|
||||
either need to add additional files to the src directory or extend
|
||||
files that are already there, depending on what functionality you're
|
||||
adding.
|
||||
</p>
|
||||
|
||||
<h3><a id="commonimpl">Implement common handling</a></h3>
|
||||
|
||||
<p>
|
||||
If the new API is applicable to more than one driver, it may
|
||||
make sense to provide some utility routines, or to factor some
|
||||
of the work into the dispatcher, to avoid reimplementing the
|
||||
same code in every driver. In the example code, this involved
|
||||
adding a member to the virDomainDefPtr struct for mapping
|
||||
between the XML API addition and the in-memory representation of
|
||||
a domain, along with updating all clients to use the new member.
|
||||
Up to this point, there have been no changes to existing
|
||||
semantics, and the new APIs will fail unless they are used in
|
||||
the same way as the older API wrappers.
|
||||
</p>
|
||||
|
||||
<h3><a id="drivercode">Implement driver handling</a></h3>
|
||||
|
||||
<p>
|
||||
The remaining patches should only touch one driver at a time.
|
||||
It is possible to implement all changes for a driver in one
|
||||
patch, but for review purposes it may still make sense to break
|
||||
things into simpler steps. Here is where the new APIs finally
|
||||
start working.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
It is always a good idea to patch the test driver in addition to the
|
||||
target driver, to prove that the API can be used for more than one
|
||||
driver.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Any cleanups resulting from the changes should be added as separate
|
||||
patches at the end of the series.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Once you have working functionality, run ninja test on each patch
|
||||
of the series before submitting patches. It may also be worth
|
||||
writing tests for the libvirt-TCK testsuite to exercise your new API,
|
||||
although those patches are not kept in the libvirt repository.
|
||||
</p>
|
||||
</body>
|
||||
</html>
|
||||
291
docs/api_extension.rst
Normal file
291
docs/api_extension.rst
Normal file
@ -0,0 +1,291 @@
|
||||
=================================
|
||||
Implementing a new API in Libvirt
|
||||
=================================
|
||||
|
||||
.. contents::
|
||||
|
||||
This document walks you through the process of implementing a new API in
|
||||
libvirt. Remember that new API consists of any new public functions, as
|
||||
well as the addition of flags or extensions of XML used by existing
|
||||
functions.
|
||||
|
||||
Before you begin coding, it is critical that you propose your changes on
|
||||
the libvirt mailing list and get feedback on your ideas to make sure
|
||||
what you're proposing fits with the general direction of the project.
|
||||
Even before doing a proof of concept implementation, send an email
|
||||
giving an overview of the functionality you think should be added to
|
||||
libvirt. Someone may already be working on the feature you want. Also,
|
||||
recognize that everything you write is likely to undergo significant
|
||||
rework as you discuss it with the other developers, so don't wait too
|
||||
long before getting feedback.
|
||||
|
||||
Adding a new API to libvirt is not difficult, but there are quite a few
|
||||
steps. This document assumes that you are familiar with C programming
|
||||
and have checked out the libvirt code from the source code repository
|
||||
and successfully built the existing tree. Instructions on how to check
|
||||
out and build the code can be found at:
|
||||
|
||||
https://libvirt.org/downloads.html
|
||||
|
||||
Once you have a working development environment, the steps to create a
|
||||
new API are:
|
||||
|
||||
#. define the public API
|
||||
#. define the internal driver API
|
||||
#. implement the public API
|
||||
#. implement the remote protocol:
|
||||
|
||||
#. define the wire protocol format
|
||||
#. implement the RPC client
|
||||
#. implement the server side dispatcher
|
||||
|
||||
#. use new API where appropriate in drivers
|
||||
#. add virsh support
|
||||
#. add common handling for new API
|
||||
#. for each driver that can support the new API:
|
||||
|
||||
#. add prerequisite support
|
||||
#. fully implement new API
|
||||
|
||||
It is, of course, possible to implement the pieces in any order, but if
|
||||
the development tasks are completed in the order listed, the code will
|
||||
compile after each step. Given the number of changes required,
|
||||
verification after each step is highly recommended.
|
||||
|
||||
Submit new code in the form of one patch per step. That's not to say
|
||||
submit patches before you have working functionality--get the whole
|
||||
thing working and make sure you're happy with it. Then use git to break
|
||||
the changes into pieces so you don't drop a big blob of code on the
|
||||
mailing list in one go. Also, you should follow the upstream tree, and
|
||||
rebase your series to adapt your patches to work with any other changes
|
||||
that were accepted upstream during your development.
|
||||
|
||||
Don't mix anything else into the patches you submit. The patches should
|
||||
be the minimal changes required to implement the functionality you're
|
||||
adding. If you notice a bug in unrelated code (i.e., code you don't have
|
||||
to touch to implement your API change) during development, create a
|
||||
patch that just addresses that bug and submit it separately.
|
||||
|
||||
Defining the public API
|
||||
-----------------------
|
||||
|
||||
The first task is to define the public API. If the new API involves an
|
||||
XML extension, you have to enhance the RelaxNG schema and document the
|
||||
new elements or attributes:
|
||||
|
||||
``docs/schemas/domaincommon.rng docs/formatdomain.html.in``
|
||||
|
||||
If the API extension involves a new function, you have to add a
|
||||
declaration in the public header, and arrange to export the function
|
||||
name (symbol) so other programs can link against the libvirt library and
|
||||
call the new function:
|
||||
|
||||
``include/libvirt/libvirt-$MODULE.h.in src/libvirt_public.syms``
|
||||
|
||||
Please consult our `coding
|
||||
style <coding-style.html#xml-element-and-attribute-naming>`__ guide on
|
||||
elements and attribute names.
|
||||
|
||||
This task is in many ways the most important to get right, since once
|
||||
the API has been committed to the repository, it's libvirt's policy
|
||||
never to change it. Mistakes in the implementation are bugs that you can
|
||||
fix. Make a mistake in the API definition and you're stuck with it, so
|
||||
think carefully about the interface and don't be afraid to rework it as
|
||||
you go through the process of implementing it.
|
||||
|
||||
Defining the internal API
|
||||
-------------------------
|
||||
|
||||
Each public API call is associated with a driver, such as a host
|
||||
virtualization driver, a network virtualization driver, a storage
|
||||
virtualization driver, a state driver, or a device monitor. Adding the
|
||||
internal API is ordinarily a matter of adding a new member to the struct
|
||||
representing one of these drivers.
|
||||
|
||||
Of course, it's possible that the new API will involve the creation of
|
||||
an entirely new driver type, in which case the changes will include the
|
||||
creation of a new struct type to represent the new driver type.
|
||||
|
||||
The driver structs are defined in:
|
||||
|
||||
``src/driver-$MODULE.h``
|
||||
|
||||
To define the internal API, first typedef the driver function prototype
|
||||
and then add a new field for it to the relevant driver struct. Then,
|
||||
update all existing instances of the driver to provide a ``NULL`` stub
|
||||
for the new function.
|
||||
|
||||
Implementing the public API
|
||||
---------------------------
|
||||
|
||||
Implementing the public API is largely a formality in which we wire up
|
||||
public API to the internal driver API. The public API implementation
|
||||
takes care of some basic validity checks before passing control to the
|
||||
driver implementation. In RFC 2119 vocabulary, this function:
|
||||
|
||||
#. SHOULD log a message with VIR_DEBUG() indicating that it is being
|
||||
called and its parameters;
|
||||
#. MUST call virResetLastError();
|
||||
#. SHOULD confirm that the connection is valid with
|
||||
virCheckConnectReturn() or virCheckConnectGoto();
|
||||
#. **SECURITY: If the API requires a connection with write privileges,
|
||||
MUST confirm that the connection flags do not indicate that the
|
||||
connection is read-only with virCheckReadOnlyGoto();**
|
||||
#. SHOULD do basic validation of the parameters that are being passed
|
||||
in, using helpers like virCheckNonNullArgGoto();
|
||||
#. MUST confirm that the driver for this connection exists and that it
|
||||
implements this function;
|
||||
#. MUST call the internal API;
|
||||
#. SHOULD log a message with VIR_DEBUG() indicating that it is
|
||||
returning, its return value, and status.
|
||||
#. MUST return status to the caller.
|
||||
|
||||
The public API calls are implemented in:
|
||||
|
||||
``src/libvirt-$MODULE.c``
|
||||
|
||||
Implementing the remote protocol
|
||||
--------------------------------
|
||||
|
||||
Implementing the remote protocol is essentially a straightforward
|
||||
exercise which is probably most easily understood by referring to the
|
||||
existing code.
|
||||
|
||||
Defining the wire protocol format
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Defining the wire protocol involves making additions to:
|
||||
|
||||
``src/remote/remote_protocol.x``
|
||||
|
||||
First, create two new structs for each new function that you're adding
|
||||
to the API. One struct describes the parameters to be passed to the
|
||||
remote function, and a second struct describes the value returned by the
|
||||
remote function. The one exception to this rule is that functions that
|
||||
return only 0 or -1 for status do not require a struct for returned
|
||||
data.
|
||||
|
||||
Second, add values to the remote_procedure enum for each new function
|
||||
added to the API.
|
||||
|
||||
Once these changes are in place, it's necessary to run 'make rpcgen' in
|
||||
the src directory to create the .c and .h files required by the remote
|
||||
protocol code. This must be done on a Linux host using the GLibC rpcgen
|
||||
program. Other rpcgen versions may generate code which results in bogus
|
||||
compile time warnings. This regenerates the following files:
|
||||
|
||||
``src/remote/remote_daemon_dispatch_stubs.h src/remote/remote_daemon_dispatch.h src/remote/remote_daemon_dispatch.c src/remote/remote_protocol.c src/remote/remote_protocol.h``
|
||||
|
||||
Implement the RPC client
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Implementing the RPC client uses the rpcgen generated .h files. The
|
||||
remote method calls go in:
|
||||
|
||||
``src/remote/remote_driver.c``
|
||||
|
||||
Each remote method invocation does the following:
|
||||
|
||||
#. locks the remote driver;
|
||||
#. sets up the method arguments;
|
||||
#. invokes the remote function;
|
||||
#. checks the return value, if necessary;
|
||||
#. extracts any returned data;
|
||||
#. frees any returned data;
|
||||
#. unlocks the remote driver.
|
||||
|
||||
Implement the server side dispatcher
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Implementing the server side of the remote function call is simply a
|
||||
matter of deserializing the parameters passed in from the remote caller
|
||||
and passing them to the corresponding internal API function. The server
|
||||
side dispatchers are implemented in:
|
||||
|
||||
``src/remote/remote_daemon_dispatch.c``
|
||||
|
||||
Again, this step uses the .h files generated by make rpcgen.
|
||||
|
||||
After all three pieces of the remote protocol are complete, and the
|
||||
generated files have been updated, it will be necessary to update the
|
||||
file:
|
||||
|
||||
``src/remote_protocol-structs``
|
||||
|
||||
This file should only have new lines added; modifications to existing
|
||||
lines probably imply a backwards-incompatible API change.
|
||||
|
||||
Use the new API internally
|
||||
--------------------------
|
||||
|
||||
Sometimes, a new API serves as a superset of existing API, by adding
|
||||
more granularity in what can be managed. When this is the case, it makes
|
||||
sense to share a common implementation by making the older API become a
|
||||
trivial wrapper around the new API, rather than duplicating the common
|
||||
code. This step should not introduce any semantic differences for the
|
||||
old API, and is not necessary if the new API has no relation to existing
|
||||
API.
|
||||
|
||||
Expose the new API in virsh
|
||||
---------------------------
|
||||
|
||||
All new API should be manageable from the virsh command line shell. This
|
||||
proves that the API is sufficient for the intended purpose, and helps to
|
||||
identify whether the proposed API needs slight changes for easier usage.
|
||||
However, remember that virsh is used to connect to hosts running older
|
||||
versions of libvirtd, so new commands should have fallbacks to an older
|
||||
API if possible; implementing the virsh hooks at this point makes it
|
||||
very easy to test these fallbacks. Also remember to document virsh
|
||||
additions.
|
||||
|
||||
A virsh command is composed of a few pieces of code. You need to define
|
||||
an array of vshCmdInfo structs for each new command that contain the
|
||||
help text and the command description text. You also need an array of
|
||||
vshCmdOptDef structs to describe the command options. Once you have
|
||||
those pieces in place you can write the function implementing the virsh
|
||||
command. Finally, you need to add the new command to the commands[]
|
||||
array. The following files need changes:
|
||||
|
||||
``tools/virsh-$MODULE.c tools/virsh.pod``
|
||||
|
||||
Implement the driver methods
|
||||
----------------------------
|
||||
|
||||
So, after all that, we get to the fun part. All functionality in libvirt
|
||||
is implemented inside a driver. Thus, here is where you implement
|
||||
whatever functionality you're adding to libvirt. You'll either need to
|
||||
add additional files to the src directory or extend files that are
|
||||
already there, depending on what functionality you're adding.
|
||||
|
||||
Implement common handling
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
If the new API is applicable to more than one driver, it may make sense
|
||||
to provide some utility routines, or to factor some of the work into the
|
||||
dispatcher, to avoid reimplementing the same code in every driver. In
|
||||
the example code, this involved adding a member to the virDomainDefPtr
|
||||
struct for mapping between the XML API addition and the in-memory
|
||||
representation of a domain, along with updating all clients to use the
|
||||
new member. Up to this point, there have been no changes to existing
|
||||
semantics, and the new APIs will fail unless they are used in the same
|
||||
way as the older API wrappers.
|
||||
|
||||
Implement driver handling
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
The remaining patches should only touch one driver at a time. It is
|
||||
possible to implement all changes for a driver in one patch, but for
|
||||
review purposes it may still make sense to break things into simpler
|
||||
steps. Here is where the new APIs finally start working.
|
||||
|
||||
It is always a good idea to patch the test driver in addition to the
|
||||
target driver, to prove that the API can be used for more than one
|
||||
driver.
|
||||
|
||||
Any cleanups resulting from the changes should be added as separate
|
||||
patches at the end of the series.
|
||||
|
||||
Once you have working functionality, run ninja test on each patch of the
|
||||
series before submitting patches. It may also be worth writing tests for
|
||||
the libvirt-TCK testsuite to exercise your new API, although those
|
||||
patches are not kept in the libvirt repository.
|
||||
@ -32,7 +32,6 @@ docs_assets = [
|
||||
|
||||
docs_html_in_files = [
|
||||
'404',
|
||||
'api_extension',
|
||||
'api',
|
||||
'apps',
|
||||
'architecture',
|
||||
@ -107,6 +106,7 @@ docs_html_in_files = [
|
||||
docs_rst_files = [
|
||||
'aclpolkit',
|
||||
'advanced-tests',
|
||||
'api_extension',
|
||||
'best-practices',
|
||||
'ci',
|
||||
'coding-style',
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user