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Re: [libvirt] libvirt-java storage support and refactoring



On Sat, Aug 02, 2008 at 06:39:44PM +0200, Chris Lalancette wrote:
> Tóth István wrote:
> > I've found that libvirt for the most part has a very perdicitble and 
> > repetitive API (great design!), and  as a result I've found myself  
> > copying the same code over and over again.
> > I've decided to make generic JNI functions, that can handle multiple 
> > libvirt functions  with function pointers.
> > The generic functions are in generic.c and they are used extensively in 
> > the new Storage JNI implementation.
> > 
> > I'd like to have your input on this architecture, my current plan is to 
> > refactor all trivial JNI functions to use these generics, unless there 
> > are objections.
> 
> (I haven't really read your patches, but...)
>
> It's definitely good to get rid of a lot of the duplicated code.
> However, you might want to take a look at the ruby-libvirt bindings
> as a different way to do it.  Basically, there are a few macros
> which generate much of the "duplicated" type code, and in my
> opinion, it's a little easier to read than lots of function
> callbacks.  The downside is that it's harder to debug with something
> like gdb, but I'm not sure that is something you do with JNI
> bindings anyway.

And while the OP is at it, take a look at a third approach used by
both the Python and OCaml bindings, namely using a script to generate
the bindings.  In OCaml we have a big Perl script which writes out the
native bindings (in C):

  http://hg.et.redhat.com/virt/applications/ocaml-libvirt--devel/?f=e8c67c00b709;file=libvirt/generator.pl
generates:
  http://hg.et.redhat.com/virt/applications/ocaml-libvirt--devel/?f=114c1e0de0c0;file=libvirt/libvirt_c.c

I've tried to generate C code which is readable, thus 'gdb' is useful.
The Python bindings are generated in a similar way.

I have in the past made comments about the 'irreducible complexity' of
generating libvirt bindings, so I won't repeat that :-)

Rich.

-- 
Richard Jones, Emerging Technologies, Red Hat  http://et.redhat.com/~rjones
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://et.redhat.com/~rjones/virt-top


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