Re: [Libvir] PATCH 16/20: add a generic logging API

This patch adds a generic API for drivers to log warning / debug / info messages. The existing error APIs are not suitable for this purpose since each time you set an error, it clears the previous one. This adds a public API virSetLogFunc allowing applications to register a callback to receive log messages. If none is registered, they are sent to the big void. It adapts the QEMU driver to use this logging API instead of qemudLog and qemudDebug(). It makes the qemud/qemud.c file register a logging callback to receive the messages & send them onto syslog/stderr as needed. There are other drivers (in particular src/xm_internal.c) where this logging API will be useful too. I've not attempted to make them use it yet though.