Re: qemu-nbd CMD_BLOCK_STATUS returns one extent in CentOS 8.0, all extents in 4.1.0 - is this a bug?

[Eric Blake]

On 11/27/19 1:35 PM, Eric Blake wrote:

> > Changing this to:
> >
> >          extents = []
> >          pos = 0
> >
> >          while pos < size:
> >              res = c.extents(pos, size - pos)["base:allocation"]
> >              for ext in res:
> >                  pos += ext.length
> >                  extents.append(ext)
> >
> > Solves the issue:
> > https://travis-ci.org/nirs/ovirt-imageio/jobs/617846324
> >
> > So I guess I answered my question but I would like to get
> > your opinion anyway.
>
> Correct, the behavior is spec-compliant, even if annoying that it 
> doesn't make as much forward progress as is possible.  Writing a loop in 
> the client is the correct behavior (the spec guarantees forward progress 
> on success, so at least that aspect of writing a loop is easier).

Oh, one other thing - your loop happens to work for your test case, but 
will be thrown off if you ever get the same status in successive calls. 
A more robust loop will coalesce consecutive ranges with the same status 
before doing any comparison of whether the overall array matches an 
expected pattern.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org