In article <1118281429.532953.2723.nullmailer@yamt.dyndns.org>,
YAMAMOTO Takashi  <yamt@mwd.biglobe.ne.jp> wrote:
> > So: am I completely wrong in my reading of the relevant source, or is
> > NetBSD's xbd backend broken?
> 
> you're right.  our (netbsd's) backends are broken.
> 
> > And no, I don't see the point in scatter/gathering a single page of I/O
> > into individual segments for each constituent sector, which is what it
> > looks like the problematic guest is doing, but that doesn't change that
> > the backend should answer it correctly.
> 
> besides that, xen_shm assumes an arbitrary request can be mapped into
> a single contiguous virtual address range.  it's wrong.

It looks like it might be possible to fix that by changing xbdback_io
to send off multiple xbdback_requests.  And with that done right, it
shouldn't be too hard to glue together request segments that can be
mapped into contiguous VM.

So I might even be able to fix this myself, if no-one more knowledgeable
is working on it.

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