[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
complexity.
Dan.
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