Filter out stale domains from xenstore listing

The xenstore database sometimes has stale domain IDs which are not
present in the hypervisor anymore. Filter these out to avoid causing
confusion

* src/xen/xs_internal.c: Filter domain IDs against HV's list
* src/xen/xen_hypervisor.h, src/xen/xen_hypervisor.c: Add new
  xenHypervisorHasDomain() method for checking ID validity

src/xen/xen_hypervisor.c

@@ -2789,6 +2789,28 @@ xenHypervisorDomainGetOSType (virDomainPtr dom)
     return ostype;
 }
 
+int
+xenHypervisorHasDomain(virConnectPtr conn,
+                       int id)
+{
+    xenUnifiedPrivatePtr priv;
+    xen_getdomaininfo dominfo;
+
+    priv = (xenUnifiedPrivatePtr) conn->privateData;
+    if (priv->handle < 0)
+        return 0;
+
+    XEN_GETDOMAININFO_CLEAR(dominfo);
+
+    if (virXen_getdomaininfo(priv->handle, id, &dominfo) < 0)
+        return 0;
+
+    if (XEN_GETDOMAININFO_DOMAIN(dominfo) != id)
+        return 0;
+
+    return 1;
+}
+
 virDomainPtr
 xenHypervisorLookupDomainByID(virConnectPtr conn,
                               int id)

src/xen/xen_hypervisor.h

@@ -23,7 +23,9 @@ int    xenHypervisorInit                 (void);
 virCapsPtr xenHypervisorMakeCapabilities (virConnectPtr conn);
 
 /* The following calls are made directly by the Xen proxy: */
-
+int
+        xenHypervisorHasDomain(virConnectPtr conn,
+                               int id);
 virDomainPtr
         xenHypervisorLookupDomainByID   (virConnectPtr conn,
                                          int id);

src/xen/xs_internal.c

@@ -543,8 +543,9 @@ int
 xenStoreNumOfDomains(virConnectPtr conn)
 {
     unsigned int num;
-    char **idlist;
-    int ret = -1;
+    char **idlist = NULL, *endptr;
+    int i, ret = -1, realnum = 0;
+    long id;
     xenUnifiedPrivatePtr priv;
 
     if (conn == NULL) {
@@ -557,10 +558,22 @@ xenStoreNumOfDomains(virConnectPtr conn)
         virXenStoreError(conn, VIR_ERR_INVALID_ARG, __FUNCTION__);
         return(-1);
     }
+
     idlist = xs_directory(priv->xshandle, 0, "/local/domain", &num);
     if (idlist) {
-        free(idlist);
-        ret = num;
+        for (i = 0; i < num; i++) {
+            id = strtol(idlist[i], &endptr, 10);
+            if ((endptr == idlist[i]) || (*endptr != 0))
+                goto out;
+
+            /* Sometimes xenstore has stale domain IDs, so filter
+               against the hypervisor's info */
+            if (xenHypervisorHasDomain(conn, (int)id))
+                realnum++;
+        }
+out:
+        VIR_FREE (idlist);
+        ret = realnum;
     }
     return(ret);
 }
@@ -577,7 +590,7 @@ xenStoreNumOfDomains(virConnectPtr conn)
  * Returns the number of domain found or -1 in case of error
  */
 static int
-xenStoreDoListDomains(xenUnifiedPrivatePtr priv, int *ids, int maxids)
+xenStoreDoListDomains(virConnectPtr conn, xenUnifiedPrivatePtr priv, int *ids, int maxids)
 {
     char **idlist = NULL, *endptr;
     unsigned int num, i;
@@ -595,6 +608,10 @@ xenStoreDoListDomains(xenUnifiedPrivatePtr priv, int *ids, int maxids)
         id = strtol(idlist[i], &endptr, 10);
         if ((endptr == idlist[i]) || (*endptr != 0))
             goto out;
+
+        /* Sometimes xenstore has stale domain IDs, so filter
+           against the hypervisor's info */
+        if (xenHypervisorHasDomain(conn, (int)id))
             ids[ret++] = (int) id;
     }
 
@@ -627,7 +644,7 @@ xenStoreListDomains(virConnectPtr conn, int *ids, int maxids)
     priv = (xenUnifiedPrivatePtr) conn->privateData;
 
     xenUnifiedLock(priv);
-    ret = xenStoreDoListDomains(priv, ids, maxids);
+    ret = xenStoreDoListDomains(conn, priv, ids, maxids);
     xenUnifiedUnlock(priv);
 
     return(ret);
@@ -1299,7 +1316,7 @@ retry:
         virReportOOMError(NULL);
         return -1;
     }
-    nread = xenStoreDoListDomains(priv, new_domids, new_domain_cnt);
+    nread = xenStoreDoListDomains(conn, priv, new_domids, new_domain_cnt);
     if (nread != new_domain_cnt) {
         // mismatch. retry this read
         VIR_FREE(new_domids);
@@ -1380,7 +1397,7 @@ retry:
         virReportOOMError(NULL);
         return -1;
     }
-    nread = xenStoreDoListDomains(priv, new_domids, new_domain_cnt);
+    nread = xenStoreDoListDomains(conn, priv, new_domids, new_domain_cnt);
     if (nread != new_domain_cnt) {
         // mismatch. retry this read
         VIR_FREE(new_domids);