[openstack-dev] RFC: Recording/providing ISO image headers in glance

Daniel P. Berrange berrange at redhat.com
Wed Jan 30 11:51:02 UTC 2013

On Wed, Jan 30, 2013 at 11:28:56AM +0000, Mac Innes, Kiall wrote:
> Just throwing this out there, I don't necessarily have an opinion either
> way..
> What about using the HTTP Range header to ask for the first X bytes of
> the image? This certainly isn't as efficient for the client as a
> dedicated API endpoint, but would not require explicit support for
> individual formats to be implemented.
> (I'm assuming there is some sort of fixed maximum length for the ISO header)

Yes, a couple of KB would do the trick.

This is obviously an option in the absence of more explicit support in
glance for this metadata.

Yet another option is to just let users/apps manually set some well known
properties when they upload.

The advantage I see to having this in glance is that applications do not
need to know how to parse ISO headers themselves, and they can rely on
the data always being directly available from glance. I feel providing
metadata about images stored is a core competancy of glance, since it
avoid the needs for each app using glance to reinvent the wheel themselves.

It could be designed as a plugin point, so we can provide plugins for
more image formats than just ISO.

> On 30/01/13 10:58, Daniel P. Berrange wrote:
> > Some apps have a need to be able to obtain ISO filesystem headers from
> > images stored in glance. Now obviously they can just download the image
> > (or part of it) and run 'isoinfo' on it, but this is really horrifically
> > inefficient/wasteful of bandwidth. It would be desirable for glance to
> > have explicit support for this in some way.
> > 
> > I've written a short wiki page describing one approach, which is to
> > make glance extract the data upon upload of an ISO and store it in
> > some well-defined metadata properties against the image.
> > 
> >     http://wiki.openstack.org/GlanceISOHeaders
> >     https://blueprints.launchpad.net/glance/+spec/iso-image-metadata
> > 
> > A completely different approach we be to ignore metadata properties
> > and add an explicit API to glance which would extract it on-demand,
> > but I feel this is a needlessly large amount of work & less convenient
> > and flexible than simply using existing metadata properties.

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