[libvirt] [PATCH 0/6 v2] Allow debug dump in case of crashes

Changes in v2 based on danpb feedback: - make libvirtd.log the default instead of syslog - do not open the libvirtd.log directly - create a new API to dump debug buffer to file output - use that new API now in the fatal signal handler This patch set main goal is to allow dumping of full debug informations for operations occuring in libvirt daemon before a crash. The principle is to save all logs to a round-robbin memory buffer (which we already do, except we never use that buffer), save the general daemon logs to a libvirtd.log file and upon reception of a fatal signal, save the memory buffer directly to the log file(s) or stderr. There is quite a few remarks about this, we already have that buffer but we don't log everything in, only what's output, that's what patch 1 changes, then we need to provide a function to dump it in emergency from signal handler so this also adds a new API for it. We also need to be cautious about what system call we operate from the signal handler, but basically we should limit ourselves here to write and sigaction which are safe there dixit POSIX. Something like killall -USR2 libvirtd allows to see the kind of output one get, an idle libvirtd is quiet, but handle/timer/fdpolls tend to be very verbose, Maybe now that this part is well debugged some of those could be suppressed or commented off. Also the buffer is a statically allocated 64KB, this should be made more flexible based on a configuration entry but it's left for another patch. Daniel