[libvirt] Question about qemuDomainLogContextNew()

Hi, Dear all I have a question, and need your help. 　　I want to output some log message to "/var/log/libvirt/qemu/instance-xxxxxx" when guest kernel crashed, so I add following the code: static int qemuProcessHandleGuestPanic(qemuMonitorPtr mon ATTRIBUTE_UNUSED, virDomainObjPtr vm, void *opaque) { ...... + qemuDomainLogContextPtr logCtxt = NULL; + if (!(logCtxt = qemuDomainLogContextNew(driver, vm, QEMU_DOMAIN_LOG_CONTEXT_MODE_START))){ + VIR_WARN("Unable to open domainlog"); + goto cleanup; + } ...... } <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< But this code cannot get the logCtxt, logCtxt = qemuDomainLogContextNew(driver, vm, QEMU_DOMAIN_LOG_CONTEXT_MODE_START) always return NULL, so I CANNOT write message to log file. Really Need your help, Thanks! Thanks Feng