Re: [libvirt] [PATCH] Query block allocation extent from QEMU monitor

On 05/13/2010 05:09 AM, Daniel P. Berrange wrote: > The virDomainGetBlockInfo API allows query physical block > extent and allocated block extent. These are normally the > same value unless storing a special format like qcow2 > inside a block device. In this scenario we can query QEMU > to get the actual allocated extent. > > + /* Set default value .. */ > info->allocation = info->physical; > > - ret = 0; > + /* ..but if guest is running & not using raw > + disk format and on a block device, then query > + highest allocated extent from QEMU */ > + if (virDomainObjIsActive(vm) && > + meta.format != VIR_STORAGE_FILE_RAW && > + S_ISBLK(sb.st_mode)) { > + qemuDomainObjPrivatePtr priv = vm->privateData; > + if (qemuDomainObjBeginJob(vm) < 0) > + goto cleanup; > + > + qemuDomainObjEnterMonitor(vm); > + ret = qemuMonitorGetBlockExtent(priv->mon, > + disk->info.alias, > + &info->allocation); This sets info->allocation to 0 if... > +int qemuMonitorGetBlockExtent(qemuMonitorPtr mon, > + const char *devname, > + unsigned long long *extent) > +{ > + int ret; > + DEBUG("mon=%p, fd=%d, devname=%p", > + mon, mon->fd, devname); > + > + if (mon->json) > + ret = qemuMonitorJSONGetBlockExtent(mon, devname, extent); > + else > + ret = qemuMonitorTextGetBlockExtent(mon, devname, extent); ...we don't have JSON support... > +int qemuMonitorTextGetBlockExtent(qemuMonitorPtr mon ATTRIBUTE_UNUSED, > + const char *devname ATTRIBUTE_UNUSED, > + unsigned long long *extent) > +{ > + /* Not supported in text monitor, but we don't want to > + * cause an error in callers in this scenario, just > + * fallback to marking the data unavailable */ > + *extent = 0; > + return 0; > +} Wouldn't it be better to check if qemu sets things to 0 (because max extent is not supported), and in that case, fall back to the original default of info->physical?