[xen-tools-discuss] Fwd: cascading xen-tools templates

[Henning Sprang]

Resending, as I believe this mail didn't make it through to the list...


---------- Forwarded message ----------
From: Henning Sprang <henning.sprang at gmail.com>
Date: Wed, Jan 16, 2008 at 12:50 AM
Subject: cascading xen-tools templates
To: xen-tools-discuss at xen-tools.org


Hi,
 I didn't work with my Xen systems a lot recently, and just these days
 upgraded some systems to the newest (3.8 something) xen-tools version.

 So, the disk part of the templates has grown enormously - admittedly
 not very much to my pleasure - I'd have liked it a lot if there would
 have been some backward compatible way, so people with simple setups
 could have kept their simple disk config - it used to be about one
 line in the template, now it's about 10 or something... sorry that I
 didn't track development enough to complain about that sooner! :)

 So the thing I want to do here is generally useful anyway, but even
 more helpful with this new setup type:

 I have a handful of different templates, but they all have the disk
 part in common - and as it is so long now, I definitely don't want to
 copy and paste it again and again - I just want to include it.

 What I came up with was reading the docs for
 Text::Template(http://search.cpan.org/~mjd/Text-Template-1.44/lib/Text/Template.pm#Including_files_into_templates)
 and created a file base-disks.tmpl that contains:

 {
    $OUT .= "disk        = [\n";
    for ( my $i = 0; $i <= $#PARTITIONS; $i++ )
    {
        $OUT .= "
 '$PARTITIONS[$i]{'imagetype'}$PARTITIONS[$i]{'image'},$device" . ( $i
 + 1 ) .",w',\n";
    }
    $OUT .= "              ]\n";
 }


 And in all templates that need the standard disk setup, I do something like:

 {
 @Disk::PARTITIONS = @PARTITIONS;
 $OUT.="# disks:\n";
 $OUT.= Text::Template::fill_in_file('base-disks.tmpl', PACKAGE => 'Disk' );
 }


 like that I can include the somewhat long disk stuff.

 Unfortunately, This is still some long code - but one line of it is a
 comment - and if the partitions variable wouldn't be defined in a my
 variable, but more in the ways described here, one wouldn't have to
 care to hand over any variable needed in the included files manually:
 http://search.cpan.org/~mjd/Text-Template-1.44/lib/Text/Template.pm#my_variables
 But I didn't try to change xen-create-image in a way that this works out yet...

 Henning