Re: [libvirt] [PATCHv8 2/4] libvirt/qemu - synchronous update of device definition

At 04/01/2011 12:19 PM, KAMEZAWA Hiroyuki Write: >>From 229cfc90781bfd7024f79db1aed8bea5963757e3 Mon Sep 17 00:00:00 2001 > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com&gt; > Date: Thu, 31 Mar 2011 18:52:24 +0900 > Subject: [PATCHv8 2/4] libvirt/qemu - synchronous update of device definition. > > At persistent modification of inactive domains, we go several steps as > - insert disk to vmdef > - assign pci address if necessary > - assign controller if necessary > - save it to file Step 2 should be after step 3.

> > If failure happens in above sequence, that implies there is inconsistency > between XML definition in file and vmdef cached in memory. So, it's better > to have some rollback method. Implementing undo in each stage doesn't seem > very neat, this patch implements a generic one. > > This patch adds 3 calls. > virDomainTemporalCopyAlloc(vmdef) > virDomainTemporalCopySync(orig, copy) > virDomainTemporalCopyUndo(orig, copy) > > CopyAlloc() will create a copy of vmdef, CopySync() is for synchronizing > copy and orginal, updating origina., CopyUndo() is for discarding for > discarding unnecessary things in copy at failure. With these, vmdef > modification can be done in following manner. > > copy = virDomainTemporalCopyAlloc(orig) > ....do update on copy > ....save updated data to its file > if (error) > virDomainTemporalCopyUndo(orig, copy); > else > virDomainTemporalCopySync(orig, copy) # this never fails. You only copy arrays in orig. How about copy all from orig to copy? And we can introduce a new API virDomainObjAssignPersistentDef() that is like the API virDomainObjAssignDef(). So vmdef modification can be done like this: copy = virDomainTemporalCopyAlloc(orig) ....do update on copy if (error) { virDomainDefFree(copy); } else { virDomainObjAssignPersistentDef(vm, copy) # this never fails. ....save updated data to its file } We can copy vmdef easily: 1. xml = virDomainDefFormat(def, VIR_DOMAIN_XML_WRITE_FLAGS) 2. newdef = virDomainDefParseString(caps, xml, VIR_DOMAIN_XML_READ_FLAGS)