qemu: don't continue loading caps if outdated

The XML format used for QEMU capabilities is not required to be
stable across releases, as we invalidate the cache whenever the
libvirt binary changes.

We none the less always try to parse te entire XML file before
we do any validity checks. Thus if we change the format of any
part of the data, or change permitted values for enums, then
libvirtd logs will be spammed with errors.

These are not in fact errors, but an expected scenario.

This change makes the loading code validate the cache timestamp
against the libvirtd timestamp immediately. If they don't match
then we stop loading the rest of the XML file.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

src/qemu/qemu_capabilities.c

@@ -1811,14 +1811,6 @@ virQEMUCapsNewBinary(const char *binary)
 }
 
 
-void
-virQEMUCapsSetInvalidation(virQEMUCapsPtr qemuCaps,
-                           bool enabled)
-{
-    qemuCaps->invalidation = enabled;
-}
-
-
 static int
 virQEMUCapsHostCPUDataCopy(virQEMUCapsHostCPUDataPtr dst,
                            virQEMUCapsHostCPUDataPtr src)
@@ -4209,11 +4201,14 @@ virQEMUCapsParseSEVInfo(virQEMUCapsPtr qemuCaps, xmlXPathContextPtr ctxt)
  *   <machine name='pc-1.0' alias='pc' hotplugCpus='yes' maxCpus='4' default='yes' numaMemSupported='yes'/>
  *   ...
  * </qemuCaps>
+ *
+ * Returns 0 on success, 1 if outdated, -1 on error
  */
 int
 virQEMUCapsLoadCache(virArch hostArch,
                      virQEMUCapsPtr qemuCaps,
-                     const char *filename)
+                     const char *filename,
+                     bool skipInvalidation)
 {
     xmlDocPtr doc = NULL;
     int ret = -1;
@@ -4241,6 +4236,31 @@ virQEMUCapsLoadCache(virArch hostArch,
         goto cleanup;
     }
 
+    if (virXPathLongLong("string(./selfctime)", ctxt, &l) < 0) {
+        virReportError(VIR_ERR_XML_ERROR, "%s",
+                       _("missing selfctime in QEMU capabilities XML"));
+        goto cleanup;
+    }
+    qemuCaps->libvirtCtime = (time_t)l;
+
+    qemuCaps->libvirtVersion = 0;
+    if (virXPathULong("string(./selfvers)", ctxt, &lu) == 0)
+        qemuCaps->libvirtVersion = lu;
+
+    if (!skipInvalidation &&
+        (qemuCaps->libvirtCtime != virGetSelfLastChanged() ||
+         qemuCaps->libvirtVersion != LIBVIR_VERSION_NUMBER)) {
+        VIR_DEBUG("Outdated capabilities in %s: libvirt changed "
+                  "(%lld vs %lld, %lu vs %lu), stopping load",
+                  qemuCaps->binary,
+                  (long long)qemuCaps->libvirtCtime,
+                  (long long)virGetSelfLastChanged(),
+                  (unsigned long)qemuCaps->libvirtVersion,
+                  (unsigned long)LIBVIR_VERSION_NUMBER);
+        ret = 1;
+        goto cleanup;
+    }
+
     if (!(str = virXPathString("string(./emulator)", ctxt))) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("missing emulator in QEMU capabilities cache"));
@@ -4260,17 +4280,6 @@ virQEMUCapsLoadCache(virArch hostArch,
     }
     qemuCaps->ctime = (time_t)l;
 
-    if (virXPathLongLong("string(./selfctime)", ctxt, &l) < 0) {
-        virReportError(VIR_ERR_XML_ERROR, "%s",
-                       _("missing selfctime in QEMU capabilities XML"));
-        goto cleanup;
-    }
-    qemuCaps->libvirtCtime = (time_t)l;
-
-    qemuCaps->libvirtVersion = 0;
-    if (virXPathULong("string(./selfvers)", ctxt, &lu) == 0)
-        qemuCaps->libvirtVersion = lu;
-
     if ((n = virXPathNodeSet("./flag", ctxt, &nodes)) < 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("failed to parse qemu capabilities flags"));
@@ -4422,6 +4431,9 @@ virQEMUCapsLoadCache(virArch hostArch,
     if (virXPathBoolean("boolean(./kvmSupportsSecureGuest)", ctxt) > 0)
         qemuCaps->kvmSupportsSecureGuest = true;
 
+    if (skipInvalidation)
+        qemuCaps->invalidation = false;
+
     ret = 0;
  cleanup:
     VIR_FREE(str);
@@ -5493,16 +5505,23 @@ virQEMUCapsNewData(const char *binary,
 static void *
 virQEMUCapsLoadFile(const char *filename,
                     const char *binary,
-                    void *privData)
+                    void *privData,
+                    bool *outdated)
 {
     virQEMUCapsPtr qemuCaps = virQEMUCapsNewBinary(binary);
     virQEMUCapsCachePrivPtr priv = privData;
+    int ret;
 
     if (!qemuCaps)
         return NULL;
 
-    if (virQEMUCapsLoadCache(priv->hostArch, qemuCaps, filename) < 0)
+    ret = virQEMUCapsLoadCache(priv->hostArch, qemuCaps, filename, false);
+    if (ret < 0)
         goto error;
+    if (ret == 1) {
+        *outdated = true;
+        goto error;
+    }
 
     return qemuCaps;
 

src/qemu/qemu_capspriv.h

@@ -37,12 +37,10 @@ virQEMUCapsNewForBinaryInternal(virArch hostArch,
                                 unsigned int microcodeVersion,
                                 const char *kernelVersion);
 
-void virQEMUCapsSetInvalidation(virQEMUCapsPtr qemuCaps,
-                                bool enabled);
-
 int virQEMUCapsLoadCache(virArch hostArch,
                          virQEMUCapsPtr qemuCaps,
-                         const char *filename);
+                         const char *filename,
+                         bool skipInvalidation);
 char *virQEMUCapsFormatCache(virQEMUCapsPtr qemuCaps);
 
 int

src/util/virfilecache.c

@@ -130,6 +130,7 @@ virFileCacheLoad(virFileCachePtr cache,
     g_autofree char *file = NULL;
     int ret = -1;
     void *loadData = NULL;
+    bool outdated = false;
 
     *data = NULL;
 
@@ -148,10 +149,12 @@ virFileCacheLoad(virFileCachePtr cache,
         goto cleanup;
     }
 
-    if (!(loadData = cache->handlers.loadFile(file, name, cache->priv))) {
+    if (!(loadData = cache->handlers.loadFile(file, name, cache->priv, &outdated))) {
-        VIR_WARN("Failed to load cached data from '%s' for '%s': %s",
+        if (!outdated) {
-                 file, name, virGetLastErrorMessage());
+            VIR_WARN("Failed to load cached data from '%s' for '%s': %s",
-        virResetLastError();
+                     file, name, virGetLastErrorMessage());
+            virResetLastError();
+        }
         ret = 0;
         goto cleanup;
     }

src/util/virfilecache.h

@@ -62,15 +62,20 @@ typedef void *
  * @filename: name of a file with cached data
  * @name: name of the cached data
  * @priv: private data created together with cache
+ * @outdated: set to true if data was outdated
  *
- * Loads the cached data from a file @filename.
+ * Loads the cached data from a file @filename. If
+ * NULL is returned, then @oudated indicates whether
+ * this was due to the data being outdated, or an
+ * error loading the cache.
  *
- * Returns cached data object or NULL on error.
+ * Returns cached data object or NULL on outdated data or error.
  */
 typedef void *
 (*virFileCacheLoadFilePtr)(const char *filename,
                            const char *name,
-                           void *priv);
+                           void *priv,
+                           bool *outdated);
 
 /**
  * virFileCacheSaveFilePtr:

tests/testutilsqemu.c

@@ -293,10 +293,9 @@ qemuTestParseCapabilitiesArch(virArch arch,
                                               virArchToString(arch));
 
     if (!(qemuCaps = virQEMUCapsNewBinary(binary)) ||
-        virQEMUCapsLoadCache(arch, qemuCaps, capsFile) < 0)
+        virQEMUCapsLoadCache(arch, qemuCaps, capsFile, true) < 0)
         goto error;
 
-    virQEMUCapsSetInvalidation(qemuCaps, false);
     return qemuCaps;
 
  error:

tests/virfilecachetest.c

@@ -110,7 +110,8 @@ testFileCacheNewData(const char *name G_GNUC_UNUSED,
 static void *
 testFileCacheLoadFile(const char *filename,
                       const char *name G_GNUC_UNUSED,
-                      void *priv G_GNUC_UNUSED)
+                      void *priv G_GNUC_UNUSED,
+                      bool *outdated G_GNUC_UNUSED)
 {
     testFileCacheObjPtr obj;
     char *data;