[Libvir] RFC [0/3]: Re-factor QEMU daemon protocol to use XDR

Daniel P. Berrange berrange at redhat.com
Wed Apr 11 12:56:29 UTC 2007

On Wed, Apr 11, 2007 at 01:54:52PM +0100, Richard W.M. Jones wrote:
> Daniel P. Berrange wrote:
> >On Wed, Apr 11, 2007 at 01:01:30PM +0100, Richard W.M. Jones wrote:
> >>I don't think those patches got memory allocation / deallocation of XDR 
> >>structures right.  Not surprising really since it's totally 
> >>undocumented!  In a bid to rectify this, I have documented how to do it 
> >>here:
> >>
> >>http://et.redhat.com/~rjones/xdr_tests/
> >
> >Nice. BTW on the subject of record streams - xdrrec_create - while very
> >nice looking on the surface, it is utterly useless because the impl
> >relies on the underlying FD / socket being in blocking mode. If you use
> >non-blocking sockets marshalling/de-marshalling will fail on the first
> >-EAGAIN the routines see, and they have no way to restart where they 
> >left off. This is why I serialized to/from a xdrmem buffer, and then used
> >my own read/write code to send to the socket where I could correctly deal
> >with non-blocking mode.
> Oh right - that totally passed me by.  When are you using non-blocking 
> sockets?  I was under the impression they were all blocking in 
> qemu_internal / libvirt_qemud.

The client end is always blocking because its only got a single connection
to worry about. The server end is completely non-blocking because it has
to deal with multiple client connections as well as I/O for the guest VM
monitor / stderr / stdout  and forking/threading just adds uneccessary

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