domain: conf: Don't validate VM ostype/arch at daemon startup

When parsing XML, we validate the passed ostype + arch combo against
the detected hypervisor capabilities. This has led to the following
problem:

- Define x86 qemu guest
- qemu is inadvertently removed from the host
- libvirtd is restarted. fails to parse VM config since arch is removed
- 'virsh list --all' is now empty, user is wondering where their VMs went

Add a new internal flag VIR_DOMAIN_DEF_PARSE_SKIP_OSTYPE_CHECKS. Use
it when loading VM and snapshot configs from disk.

https://bugzilla.redhat.com/show_bug.cgi?id=1043572

src/conf/domain_conf.c

@@ -14655,17 +14655,8 @@ virDomainDefParseXML(xmlDocPtr xml,
             goto error;
     }
 
-    if (!virCapabilitiesSupportsGuestOSType(caps, def->os.type)) {
-        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
-                       _("no support found for os <type> '%s'"),
-                       def->os.type);
-        goto error;
-    }
-
     tmp = virXPathString("string(./os/type[1]/@arch)", ctxt);
-    if (tmp) {
-        def->os.arch = virArchFromString(tmp);
-        if (!def->os.arch) {
+    if (tmp && !(def->os.arch = virArchFromString(tmp))) {
         virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
                        _("Unknown architecture %s"),
                        tmp);
@@ -14673,6 +14664,17 @@ virDomainDefParseXML(xmlDocPtr xml,
     }
     VIR_FREE(tmp);
 
+    def->os.machine = virXPathString("string(./os/type[1]/@machine)", ctxt);
+
+    if (!(flags & VIR_DOMAIN_DEF_PARSE_SKIP_OSTYPE_CHECKS)) {
+        if (!virCapabilitiesSupportsGuestOSType(caps, def->os.type)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("no support found for os <type> '%s'"),
+                           def->os.type);
+            goto error;
+        }
+
+        if (def->os.arch) {
             if (!virCapabilitiesSupportsGuestArch(caps, def->os.arch)) {
                 virReportError(VIR_ERR_INTERNAL_ERROR,
                                _("No guest options available for arch '%s'"),
@@ -14701,7 +14703,6 @@ virDomainDefParseXML(xmlDocPtr xml,
             }
         }
 
-    def->os.machine = virXPathString("string(./os/type[1]/@machine)", ctxt);
         if (!def->os.machine) {
             const char *defaultMachine = virCapabilitiesDefaultGuestMachine(caps,
                                                                             def->os.type,
@@ -14710,6 +14711,8 @@ virDomainDefParseXML(xmlDocPtr xml,
             if (VIR_STRDUP(def->os.machine, defaultMachine) < 0)
                 goto error;
         }
+    }
+
 
     /*
      * Booting options for different OS types....
@@ -21591,7 +21594,8 @@ virDomainObjListLoadConfig(virDomainObjListPtr doms,
         goto error;
     if (!(def = virDomainDefParseFile(configFile, caps, xmlopt,
                                       expectedVirtTypes,
-                                      VIR_DOMAIN_DEF_PARSE_INACTIVE)))
+                                      VIR_DOMAIN_DEF_PARSE_INACTIVE |
+                                      VIR_DOMAIN_DEF_PARSE_SKIP_OSTYPE_CHECKS)))
         goto error;
 
     if ((autostartLink = virDomainConfigFile(autostartDir, name)) == NULL)
@@ -21641,7 +21645,8 @@ virDomainObjListLoadStatus(virDomainObjListPtr doms,
                                       VIR_DOMAIN_DEF_PARSE_STATUS |
                                       VIR_DOMAIN_DEF_PARSE_ACTUAL_NET |
                                       VIR_DOMAIN_DEF_PARSE_PCI_ORIG_STATES |
-                                      VIR_DOMAIN_DEF_PARSE_CLOCK_ADJUST)))
+                                      VIR_DOMAIN_DEF_PARSE_CLOCK_ADJUST |
+                                      VIR_DOMAIN_DEF_PARSE_SKIP_OSTYPE_CHECKS)))
         goto error;
 
     virUUIDFormat(obj->def->uuid, uuidstr);

src/conf/domain_conf.h

@@ -2530,6 +2530,10 @@ typedef enum {
     /* parse only source half of <disk> */
     VIR_DOMAIN_DEF_PARSE_DISK_SOURCE     = 1 << 7,
     VIR_DOMAIN_DEF_PARSE_VALIDATE        = 1 << 8,
+    /* don't validate os.type and arch against capabilities. Prevents
+     * VMs from disappearing when qemu is removed and libvirtd is restarted
+     */
+    VIR_DOMAIN_DEF_PARSE_SKIP_OSTYPE_CHECKS = 1 << 9,
 } virDomainDefParseFlags;
 
 typedef enum {

src/conf/snapshot_conf.c

@@ -270,6 +270,9 @@ virDomainSnapshotDefParse(xmlXPathContextPtr ctxt,
          * clients will have to decide between best effort
          * initialization or outright failure.  */
         if ((tmp = virXPathString("string(./domain/@type)", ctxt))) {
+            int domainflags = VIR_DOMAIN_DEF_PARSE_INACTIVE;
+            if (flags & VIR_DOMAIN_SNAPSHOT_PARSE_INTERNAL)
+                domainflags |= VIR_DOMAIN_DEF_PARSE_SKIP_OSTYPE_CHECKS;
             xmlNodePtr domainNode = virXPathNode("./domain", ctxt);
 
             VIR_FREE(tmp);
@@ -280,8 +283,7 @@ virDomainSnapshotDefParse(xmlXPathContextPtr ctxt,
             }
             def->dom = virDomainDefParseNode(ctxt->node->doc, domainNode,
                                              caps, xmlopt,
-                                             expectedVirtTypes,
-                                             VIR_DOMAIN_DEF_PARSE_INACTIVE);
+                                             expectedVirtTypes, domainflags);
             if (!def->dom)
                 goto cleanup;
         } else {