[Libguestfs] [PATCH nbdkit v2] Add the ability to write plugins in golang.

[Daniel P. Berrangé]

On Thu, Apr 23, 2020 at 10:03:45AM +0100, Richard W.M. Jones wrote:
> On Tue, Apr 21, 2020 at 05:07:43PM +0100, Daniel P. Berrangé wrote:
> > On Tue, Apr 21, 2020 at 11:44:59AM +0100, Richard W.M. Jones wrote:
> > > Thanks: Dan Berrangé
> > > 
> > > XXX UNFINISHED:
> > > 
> > >  - Is using uintptr for the handle a good idea?  Plugins must return
> > >    something != 0.  In other languages we would allow plugins to
> > >    return an arbitrary object here, but this is not possible in golang
> > >    because of lack of GC roots.
> > 
> > Yeah, this is the bit that looks wierd to me when thinking about this
> > from a Go dev POV.  You asked me on IRC whether we should have a separate
> > interface for a connection object, and this makes me think that we should
> > indeed do that.
> ...
> 
> This is what the patch looks like with a separate connection object.
> It appears to work.
> 
> Rich.
> 
> -- 
> Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> virt-df lists disk usage of guests without needing to install any
> software inside the virtual machine.  Supports Linux and Windows.
> http://people.redhat.com/~rjones/virt-df/

> From a929cff8745f21df913ea3230741dc7f2a1c016e Mon Sep 17 00:00:00 2001
> From: "Richard W.M. Jones" <rjones at redhat.com>
> Date: Thu, 9 Apr 2020 12:45:10 +0100
> Subject: [PATCH] Add the ability to write plugins in golang.
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
> 
> Thanks: Dan Berrangé
> 
> XXX UNFINISHED:
> 
>  - Default can_* methods are hard to implement.  Ideally we would be
>    able to test if a user plugin implements a particular callback
>    (eg. TestPlugin.PWrite) or else defaults to the default callback,
>    but even with reflection I don't think this is possible in golang.
>    [Discussed on IRC: We decided the only option was to go for
>     nbdkit-sh-plugin style can_* methods]
> 
>  - Write wrappers etc for all the other methods.
> 
>  - Write documentation.
> ---
>  plugins/golang/nbdkit-golang-plugin.pod       |  34 +++
>  configure.ac                                  |  32 +++
>  plugins/golang/Makefile.am                    |  80 ++++++
>  .../src/libguestfs.org/nbdkit/wrappers.h      |  41 +++
>  plugins/golang/config-test.go                 |  38 +++
>  .../src/libguestfs.org/nbdkit/nbdkit.go       | 270 ++++++++++++++++++
>  .../golang/src/libguestfs.org/nbdkit/utils.go |  75 +++++
>  .../src/libguestfs.org/nbdkit/wrappers.go     | 102 +++++++
>  plugins/golang/test/run-test.sh               |  42 +++
>  plugins/golang/test/test.go                   | 119 ++++++++
>  .gitignore                                    |   2 +
>  README                                        |   4 +
>  12 files changed, 839 insertions(+)
>  create mode 100644 plugins/golang/nbdkit-golang-plugin.pod
>  create mode 100644 plugins/golang/Makefile.am
>  create mode 100644 plugins/golang/src/libguestfs.org/nbdkit/wrappers.h
>  create mode 100644 plugins/golang/config-test.go
>  create mode 100644 plugins/golang/src/libguestfs.org/nbdkit/nbdkit.go
>  create mode 100644 plugins/golang/src/libguestfs.org/nbdkit/utils.go
>  create mode 100644 plugins/golang/src/libguestfs.org/nbdkit/wrappers.go
>  create mode 100755 plugins/golang/test/run-test.sh
>  create mode 100644 plugins/golang/test/test.go

I think this design with two interfaces looks pretty nice from the
Go plugin implementors POV now.


Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|