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Re: [libvirt] [BUG] When PLUG a bridge interface to an active VM, the generated LIVE and CONFIG mac address are different



> On 8/28/19 11:42 AM, wujing (O) wrote:
> >>>>> On 8/22/19 10:43 AM, Xu Yandong (Yandong Xu) wrote:
> >>>> That possibly might be out of scope, but autofilling the mac
> >>>> address as early as virDomainNetDefParseXML also is not ideal.
> >>>
> >>> We have pushed a patch bellow that can restore the situation to an
> >>> older
> >> state.
> >>>
> >>> Subject: [PATCH] qemu: use the same def when attaching device live
> >>> and config
> >>>
> >>> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c index
> >>> 617d7d5..eca54d0 100644
> >>> --- a/src/qemu/qemu_driver.c
> >>> +++ b/src/qemu/qemu_driver.c
> >>> @@ -8615,6 +8615,22 @@
> >> qemuDomainAttachDeviceLiveAndConfig(virDomainObjPtr vm,
> >>>        if (!(caps = virQEMUDriverGetCapabilities(driver, false)))
> >>>            goto cleanup;
> >>>
> >>> +    if (flags & VIR_DOMAIN_AFFECT_CONFIG &&
> >>> +        flags & VIR_DOMAIN_AFFECT_LIVE) {
> >>> +        /* If we are affecting both CONFIG and LIVE
> >>> +         * use the same xml of device preferentially
> >>> +         * to make the configuration consistent.
> >>> +         */
> >>> +        devLive = virDomainDeviceDefParse(xml, vm->def,
> >>
> >> This use of vm->def prefers live XML. This means that for instance
> >> PCI address are assigned based on current PCI layout in live XML
> >> which in general is different to inactive XML.
> >>
> >> And it's not only PCI addresses, we autogenerate some out aspects of
> >> <interface/> (e.g. model) and even more for other devices. Just take
> >> a look at qemuDomainDeviceDefPostParse(). All functions there which
> >> take domain def as an argument do so because they are basing
> >> autogenerated value on domain definition. Plus there's more in parser
> code.
> >>
> >> While your patch might work for your use case, it can break others.
> >>
> >> BTW: have you read the original commit that caused this? I'm failing
> >> to see how we would not re-introduce the problem with your patch. If
> >> you're using live XML to validate/generate device addresses, how can
> >> we generate valid address for inactive XML?
> >>
> >
> > This patch is a little different with the original commit, since we
> > only prefer live XML when using LIVE AND CONFIG flags at the same time.
> Still parse separate device def if attach with only one flag.
> > So this patch is kinda a combination of 1e0534a7702 and 55ce6564634, just
> to narrow down the problem influence.
> >
> > And I verified as the steps in
> https://bugzilla.redhat.com/show_bug.cgi?id=1559867, work as expected.
> 
> Well, then try to coldplug <hostdev mode='subsystem' type='scsi'/> (that is
> only to inactive XML), and then try hotplug different <hostdev type'scsi'/> to
> both live and inactive XMLs and the bug will reproduce.
> Problem is, that inactive XML contains a device which is not contained in live
> XML and thus when generating device address based solely on live XML a
> conflicting address is generated.
> 
> If we'd prefer inactive XML in your patch then the steps in my reproducer
> need to be swapped. At any rate, the issue is still there.

You are right, but I found a new issue on current solution.
Test as steps below.
1. Having a running vm
## virsh list
 Id    Name   State
----------------------                                                  │~                                                 
 1    rhel   running   

2. prepare 2 scsi hostdev xml using the same address
## cat h1.xml
<hostdev mode='subsystem' type='scsi' managed='no'>                        
  <source>                                                                  
    <adapter name='scsi_host2'/>                                          
    <address bus='0' target='0' unit='0'/>                                  
  </source>  
  <address type='drive' controller='0' bus='0' target='0' unit='2'/>                                                              
</hostdev>    

## cat h2.xml
<hostdev mode='subsystem' type='scsi' managed='no'>                        
  <source>                                                                  
    <adapter name='scsi_host3'/>                                          
    <address bus='0' target='0' unit='0'/>                                  
  </source>   
  <address type='drive' controller='0' bus='0' target='0' unit='2'/>                                                             
</hostdev>  

3. attach 2 hostdev to vm with 'attach-device --config'
## virsh attach-device rhel h1.xml --config
Device attached successfully

## virsh attach-device rhel h2.xml --config
Device attached successfully

4. Check the vm's xml with 'dumpxml --inactive'
## virsh dumpxml rhel --inactive
...
    <hostdev mode='subsystem' type='scsi' managed='no'>
      <source>
        <adapter name='scsi_host2'/>
        <address bus='0' target='0' unit='0'/>
      </source>
      <address type='drive' controller='0' bus='0' target='0' unit='2'/>
    </hostdev>
    <hostdev mode='subsystem' type='scsi' managed='no'>
      <source>
        <adapter name='scsi_host3'/>
        <address bus='0' target='0' unit='0'/>
      </source>
      <address type='drive' controller='0' bus='0' target='0' unit='2'/>
    </hostdev>
...

a) Looks like libvirt can not verify if user configured the same address for different scsi hostdevs.
Because virDomainHostdevDefPostParse only calls virDomainDriveAddressIsUsedByDisk to check 
if address is used by other disks, but no check if used by other hostdevs.
And qemuDomainAttachDeviceConfig calls virDomainHostdevFind to check duplicate devices by
src addr and other stuff, not including addr in vm.

Should that be fixed?

b) If we fixed a), then we can get a devConf that both fits to live and config xml by
passing devLive  and domainPersistentDef to virDomainDeviceDefCopy.

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 617d7d5..eca54d0 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -8615,6 +8615,22 @@ qemuDomainAttachDeviceLiveAndConfig(virDomainObjPtr vm,
     if (!(caps = virQEMUDriverGetCapabilities(driver, false)))
         goto cleanup;

+    if (flags & VIR_DOMAIN_AFFECT_CONFIG &&
+        flags & VIR_DOMAIN_AFFECT_LIVE) {
+        devLive = virDomainDeviceDefParse(xml, vm->def,
+                                          caps, driver->xmlopt,
+                                          parse_flags);
+        if (!devLive)
+            goto cleanup;
+        vmdef = virDomainObjCopyPersistentDef(vm, caps, driver->xmlopt);
+        if (!vmdef)
+            goto cleanup;
+        /* Use persistent vm def to get a device def copy
+         */
+        devConf = virDomainDeviceDefCopy(devLive, vmdef, caps, driver->xmlopt);
+        if (!devConf)
+            goto cleanup;
+    }

If devLive fits to vmdef, then we get a compatible devConf, or just fail and return.

Wu Jing


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