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

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.
---
 v2v/output_rhv_upload.ml | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/v2v/output_rhv_upload.ml b/v2v/output_rhv_upload.ml
index f5e0e6b1c..d8f608cff 100644
--- 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"
 let pidfile_timeout = 30
 let finalization_timeout = 5*60
 
@@ -139,14 +140,14 @@ class output_rhv_upload output_alloc output_conn
    *)
   let error_unless_nbdkit_python_plugin_working ()      let cmd = sprintf
"nbdkit %s %s --dump-plugin >/dev/null"
-                      Python_script.python
+                      nbdkit_python_plugin
                       (quote (Python_script.path plugin_script)) in
     debug "%s" cmd;
     if Sys.command cmd <> 0 then
       error (f_"nbdkit %s plugin is not installed or not working.  It is
required if you want to use ‘-o rhv-upload’.
 
 See also the virt-v2v-output-rhv(1) manual.")
-            Python_script.python
+            nbdkit_python_plugin
   in
 
   (* Check that nbdkit was compiled with SELinux support (for the
@@ -209,7 +210,7 @@ See also the virt-v2v-output-rhv(1) manual.")
       "--newstyle";             (* use newstyle NBD protocol *)
       "--exportname"; "/";
 
-      Python_script.python;     (* use the nbdkit Python 3 plugin *)
+      nbdkit_python_plugin;     (* use the nbdkit Python plugin *)
       Python_script.path plugin_script; (* Python plugin script *)
     ] in
     let args = if verbose () then args @ ["--verbose"] else args in
-- 
2.17.2

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.
> ---
>  v2v/output_rhv_upload.ml | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/v2v/output_rhv_upload.ml b/v2v/output_rhv_upload.ml
> index f5e0e6b1c..d8f608cff 100644
> --- 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"
>  let pidfile_timeout = 30
>  let finalization_timeout = 5*60
>  
> @@ -139,14 +140,14 @@ class output_rhv_upload output_alloc output_conn
>     *)
>    let error_unless_nbdkit_python_plugin_working () >      let cmd =
sprintf "nbdkit %s %s --dump-plugin >/dev/null"
> -                      Python_script.python
> +                      nbdkit_python_plugin
>                        (quote (Python_script.path plugin_script)) in
>      debug "%s" cmd;
>      if Sys.command cmd <> 0 then
>        error (f_"nbdkit %s plugin is not installed or not working.  It
is required if you want to use ‘-o rhv-upload’.
>  
>  See also the virt-v2v-output-rhv(1) manual.")
> -            Python_script.python
> +            nbdkit_python_plugin
>    in
>  
>    (* Check that nbdkit was compiled with SELinux support (for the
> @@ -209,7 +210,7 @@ See also the virt-v2v-output-rhv(1) manual.")
>        "--newstyle";             (* use newstyle NBD protocol *)
>        "--exportname"; "/";
>  
> -      Python_script.python;     (* use the nbdkit Python 3 plugin *)
> +      nbdkit_python_plugin;     (* use the nbdkit Python plugin *)
>        Python_script.path plugin_script; (* Python plugin script *)
>      ] in
>      let args = if verbose () then args @ ["--verbose"] else args
in
> -- 
ACK

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://people.redhat.com/~rjones/virt-top

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].

I would dearly love to drop Python 2 support everywhere, but I don't
think we can do that realisticly before the Python 2 EOL
(https://pythonclock.org/) which is another 12 months away.

I wonder if there's a better way we can solve this?  I don't have any
immediate ideas ...

Rich.


[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’.


-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org

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