[Libguestfs] [PATCH nbdkit 1/2] tests/test-python-plugin.py: Allow test to use large disks

[Richard W.M. Jones]

On Wed, Dec 22, 2021 at 12:47:59AM +0200, Nir Soffer wrote:
> On Wed, Dec 22, 2021 at 12:36 AM Richard W.M. Jones <rjones at redhat.com> wrote:
> >
> > On Tue, Dec 21, 2021 at 10:25:35PM +0000, Richard W.M. Jones wrote:
> > > On Wed, Dec 22, 2021 at 12:21:25AM +0200, Nir Soffer wrote:
> > > > It would be help also if we can test extents argument, currently the
> > > > plugin ignores the argument so we did not detect the issue with the
> > > > wrong format string.
> > >
> > > OK, I'll take a look.
> >
> > I see - the plugin function is defined just to return the extents sent
> > in (for testing):
> >
> >   def extents(h, count, offset, flags):
> >       return cfg.get('extents', [])
> >
> > This means we don't test the parameters.  However to test those
> > realistically I suppose we would really need to support sparse disks
> > in this test plugin, which seems quite tricky.
> 
> I think what can work is this:
> 
> - pass the actual extents to the plugin
>
> For example empty sparse file:
> 
>    extents = [(0, 10 * GiB, nbdkit.EXTENT_ZERO)]
> 
> Now when we request:
> 
>     extents(4*GB -1, 0, 0)
> 
> The plugin can return:
> 
>      return [(0, count, nbdkit.EXTENT_ZERO)]

Isn't this what the code above already does?

> The logic to return extents from the existing list is a little tricky. I have
> similar code in a memory backend for imageio (in review):
> https://github.com/oVirt/ovirt-imageio/pull/7/commits/9068f84c96f1239d841fbfe7e80296be7be0a245
> 
> And this is also the code for getting extents from imageio, posted here:
> https://listman.redhat.com/archives/libguestfs/2021-December/msg00197.html

I'm confused about this bit.

Rich.

-- 
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