If you want to set block device I/O tuning values that end with '_max' and there is nothing else set, libvirt emits an error. In particular: error: internal error: Unexpected error That's an unknown error. That is because *_max values depend on their respective non-_max values. QEMU even says that in the error message sent as a response to the monitor command: "error": {"class": "GenericError", "desc": "bps_max/iops_max require corresponding bps/iops values"} the problem was that we didn't know that and there was no check for it. Adding such check makes sure that there will be less confused users. Signed-off-by: Martin Kletzander <mkletzan(a)redhat.com&gt; --- src/qemu/qemu_driver.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c index a7202ed3e3a1..d73238a66c66 100644 --- a/src/qemu/qemu_driver.c +++ b/src/qemu/qemu_driver.c @@ -17391,6 +17391,25 @@ qemuDomainSetBlockIoTune(virDomainPtr dom, } if (!set_size_iops) info.size_iops_sec = oldinfo->size_iops_sec; + +#define CHECK_MAX(val) \ + do { \ + if (info.val##_max && !info.val) { \ + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, \ + _("Value '%s' cannot be set if " \ + "'%s' is not set"), \ + #val "_max", #val); \ + goto endjob; \ + } \ + } while (false); + + CHECK_MAX(total_bytes_sec); + CHECK_MAX(read_bytes_sec); + CHECK_MAX(write_bytes_sec); + CHECK_MAX(total_iops_sec); + CHECK_MAX(read_iops_sec); + CHECK_MAX(write_iops_sec); + qemuDomainObjEnterMonitor(driver, vm); ret = qemuMonitorSetBlockIoThrottle(priv->mon, device, &info, supportMaxOptions); -- 2.8.3