[Libvir] Re: support for hvm guests

[Anthony Liguori]

Jim Fehlig wrote:
>
> Tomorrow ended up being several days later :-).  I looked at this 
> again today and must say that this is a frustrating bug - feeling like 
> some CS101 student.
>
> So I was wrong in stating that xend does not respond to the create op 
> issued by libvirt.  I get the expected response from xend but the 
> connection is not closed upon completing the request, thus I set in 
> some read loop in libvirt waiting for eof.  I stepped through the 
> request processing code in xend for create op for both paravirtualized 
> and hvm guests and all seems fine, i.e. request is processed, 
> finished, socket closed, etc. in httpserver.py.  Looking at a packet 
> trace shows connection is terminated for paravirt case (which breaks 
> out of the read loop in libvirt) but not so for hvm case.

The proper way to do the S-Expression RPC (or XML-RPC for that matter) 
is to look at the Content-Length header in the response and read back 
that much data (close()'ing the connection once you've gotten that 
amount).  We shouldn't wait for EOF to occur to stop reading.

There was a patch recently that changed the read() behavior to read in 
larger amounts.  It appears that when this was added, the behavior was 
changed to expect EOF.  Sorry, I should have looked at that patch more 
carefully.  If you revert xend_post to the older code, things should go 
back to working.

> Don't think I want to waste anymore time with this bug since the http 
> / sexp interface is going away - which brings me to a question.  Why 
> is libvirt still using this interface and not xmlrpc?  Perhaps my time 
> would be better spent moving libvirt to this interface.  I would like 
> to submit the hvm patch for libvirt but can't reliably test it at this 
> point.

wrt XML-RPC, I think I'm to blame for that.  I've not gotten around to 
modifying the internals of libvirt to switch between 
XML-RPC/S-Expression.  I'd suggest just reverting the xend_post to the 
older code so you can keep making progress.

Regards,

Anthony Liguori

> Regards,
> Jim
>