Libguestfs - Jan 2019 - Re: [PATCH] v2v: -o rhv-upload: decouple name of nbdkit python plugin

On Monday, 7 January 2019 14:30:00 CET Richard W.M. Jones
wrote:
> On Thu, Dec 13, 2018 at 06:58:30PM +0100, Pino Toscano wrote:
> > Do not assume that the Python plugin of nbdkit has the same name of
the
> > Python interpreter.
> > 
> > Use the default upstream name of nbdkit to identify it; downstream
> > distributions must adjust this variable, in case they rename the
Python
> > plugin of nbdkit.
> 
> I'm not saying this is wrong, but it does break "out of the
box" -o
> rhv-upload.  It means that to get it to work on Fedora we _have_ to
> patch:
> 
> > --- a/v2v/output_rhv_upload.ml
> > +++ b/v2v/output_rhv_upload.ml
> > @@ -78,6 +78,7 @@ let parse_output_options options > >  
> >    { rhv_cafile; rhv_cluster; rhv_direct; rhv_verifypeer }
> >  
> > +let nbdkit_python_plugin = "python"
> 
> to change this "python3" [1].
Yes, this is correct.  This follows the fact that on Fedora the
Python 3 plugin is renamed, so the "OOTB experience" is already
"different" because of that.

Also, the previous name ("python3") for the nbdkit plugin was broken
everywhere but on Fedora, which basically breaks the "OOTB" experience
for any other distro...
> [1] By the way, the failure is weird, non-obvious and non-actionable,
> so here it is:
> 
> nbdkit python
'/home/rjones/d/libguestfs-master/tmp/v2v.xSFDLk/rhv-upload-plugin.py'
--dump-plugin >/dev/null
>   File
"/home/rjones/d/libguestfs-master/tmp/v2v.xSFDLk/rhv-upload-plugin.py",
line 3
> SyntaxError: Non-ASCII character '\xe2' in file
/home/rjones/d/libguestfs-master/tmp/v2v.xSFDLk/rhv-upload-plugin.py on line 3,
but no encoding declared; see http://python.org/dev/peps/pep-0263/ for details
> nbdkit: error:
/home/rjones/d/libguestfs-master/tmp/v2v.xSFDLk/rhv-upload-plugin.py: error
running this script
> virt-v2v: error: nbdkit python plugin is not installed or not working.  It 
> is required if you want to use ‘-o rhv-upload’.
At least it fails ;)

One option I see is to export, as part of the nbdkit Python module
interface, the equivalent of sys.version_info: this way, the scripts
can detect which python version is the plugin linked with:

  if nbdkit.python_version_info[0] != 3:
    error("this script is for Python 3")

OTOH, it will not help with the above case, as there is a syntax error
even before a check can be reached...

-- 
Pino Toscano

On Mon, Jan 07, 2019 at 04:41:17PM +0100, Pino Toscano
wrote:
> One option I see is to export, as part of the nbdkit Python module
> interface, the equivalent of sys.version_info: this way, the scripts
> can detect which python version is the plugin linked with:
nbdkit >= 1.8 exports the Python version in ‘--dump-plugin’ output:

$ nbdkit python --dump-plugin
...
python_version=2.7.15

And where it's available, the PEP-384 ABI version:

$ nbdkit python3 --dump-plugin
...
python_version=3.7.2
python_pep_384_abi_version=3

I will try to see if we can parse this easily ...

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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On Mon, Jan 07, 2019 at 08:08:05PM +0000, Richard W.M. Jones
wrote:
> On Mon, Jan 07, 2019 at 04:41:17PM +0100, Pino Toscano wrote:
> > One option I see is to export, as part of the nbdkit Python module
> > interface, the equivalent of sys.version_info: this way, the scripts
> > can detect which python version is the plugin linked with:
> 
> nbdkit >= 1.8 exports the Python version in ‘--dump-plugin’ output:
> 
> $ nbdkit python --dump-plugin
> ...
> python_version=2.7.15
> 
> And where it's available, the PEP-384 ABI version:
> 
> $ nbdkit python3 --dump-plugin
> ...
> python_version=3.7.2
> python_pep_384_abi_version=3
> 
> I will try to see if we can parse this easily ...
I started to write something along these lines and I hate it already.

However then I wondered: shouldn't all of this be ./configure options,
eg:

  ./configure --with-virt-v2v-python-interpreter=/usr/bin/python3 \
              --with-virt-v2v-nbdkit-python=python3

or something similar?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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