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Re: [libvirt] [PATCH] macvtap: libvirtd forgot macvtap device name during a shutdown/restart cycle

On 11/02/2010 11:47 AM, Daniel P. Berrange wrote:
On Tue, Nov 02, 2010 at 11:35:44AM -0400, Stefan Berger wrote:
During a shutdown/restart cycle libvirtd forgot the macvtap device name
that it had created on behalf of a VM so that a stale macvtap device
remained on the host when the VM terminated. Libvirtd has to actively
tear down a macvtap device and it uses its name for identifying which
device to tear down.

The solution is to not blank out the<target dev='...'/>  completely, but
only blank it out on VMs that are not active. So, if a VM is active, the
device name makes it into the XML and is also being parsed. If a VM is
not active, the device name is discarded.

Signed-off-by: Stefan Berger<stefanb us ibm com>

  src/conf/domain_conf.c |    5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

Index: libvirt-acl/src/conf/domain_conf.c
--- libvirt-acl.orig/src/conf/domain_conf.c
+++ libvirt-acl/src/conf/domain_conf.c
@@ -2343,7 +2343,8 @@ virDomainNetDefParseXML(virCapsPtr caps,
          def->data.direct.linkdev = dev;
          dev = NULL;

-        VIR_FREE(ifname);
+        if ((flags&  VIR_DOMAIN_XML_INACTIVE))
+            VIR_FREE(ifname);
The conditional isn't required here - it is already dealt
with earlier on in the file. Just remove the VIR_FREE

The conditional further above is this code fragment here:

            } else if ((ifname == NULL) &&
                       xmlStrEqual(cur->name, BAD_CAST "target")) {
                ifname = virXMLPropString(cur, "dev");
                if ((ifname != NULL) &&
                    ((flags & VIR_DOMAIN_XML_INACTIVE) &&
                      (STRPREFIX((const char*)ifname, "vnet")))) {
                    /* An auto-generated target name, blank it out */

Unfortunately it is also testing for the prefix 'vnet'.

In case of a macvtap device I don't want to pick up the name of the macvtap device from the XML unless it's attached to a running domain. So that's why I remove it above.

If the domain went down without libvirt 'seeing' it then we miessed out on tearing it down and in that case there may be a stale device, but I don't support this case. So I also want to have that cleared.

Further, I also don't accept user-provided interface names for the reason of tear-down in case of failures while trying to start a VM. In the failure-case it is not clear anymore whether the name was user-provided and was previously created and needs to be torn down or simply is a user-provided name of an interface that wasn't created and thus should not be torn down because it may actually be clashing with the user-provided name of a running VM. I had that before and this ended up running danger of tearing down interfaces of running VMs when a failure-path was invoked.

So, in case a ifname is given in case of macvtap (type 'direct') it means it was started before and needs to be torn down. After every tear-down the ifname is also free()d.

@@ -5801,6 +5802,8 @@ virDomainNetDefFormat(virBufferPtr buf,
          virBufferAddLit(buf, "/>\n");
                                      "      ");
+        if ((flags&  VIR_DOMAIN_XML_INACTIVE))
+            VIR_FREE(def->ifname);
This seems dubious. Formatting XML should never require
changing 'def' at all.

Let me remove it and test it only with the modification above kept as-is.


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