qemu: Add libvirt version check to refresh capabilities algorithm

Rather than an algorithm based solely on libvirtd ctime to refresh the
capabilities add the element of the libvirt build version into the equation.
Since that version wouldn't be there prior to this code being run - don't
fail on reading the capabilities if not found. In this case, the cache
will always be rebuilt when a new libvirt version is installed.

src/qemu/qemu_capabilities.c

@@ -2605,6 +2605,7 @@ int virQEMUCapsProbeQMP(virQEMUCapsPtr qemuCaps,
  * <qemuCaps>
  *   <qemuctime>234235253</qemuctime>
  *   <selfctime>234235253</selfctime>
+ *   <selfvers>1002016</selfvers>
  *   <usedQMP/>
  *   <flag name='foo'/>
  *   <flag name='bar'/>
@@ -2617,7 +2618,8 @@ int virQEMUCapsProbeQMP(virQEMUCapsPtr qemuCaps,
  */
 static int
 virQEMUCapsLoadCache(virQEMUCapsPtr qemuCaps, const char *filename,
-                     time_t *qemuctime, time_t *selfctime)
+                     time_t *qemuctime, time_t *selfctime,
+                     unsigned long *selfvers)
 {
     xmlDocPtr doc = NULL;
     int ret = -1;
@@ -2627,6 +2629,7 @@ virQEMUCapsLoadCache(virQEMUCapsPtr qemuCaps, const char *filename,
     xmlXPathContextPtr ctxt = NULL;
     char *str = NULL;
     long long int l;
+    unsigned long lu;
 
     if (!(doc = virXMLParseFile(filename)))
         goto cleanup;
@@ -2660,6 +2663,10 @@ virQEMUCapsLoadCache(virQEMUCapsPtr qemuCaps, const char *filename,
     }
     *selfctime = (time_t)l;
 
+    *selfvers = 0;
+    if (virXPathULong("string(./selfvers)", ctxt, &lu) == 0)
+        *selfvers = lu;
+
     qemuCaps->usedQMP = virXPathBoolean("count(./usedQMP) > 0",
                                         ctxt) > 0;
 
@@ -2798,6 +2805,8 @@ virQEMUCapsSaveCache(virQEMUCapsPtr qemuCaps, const char *filename)
                       (long long)qemuCaps->ctime);
     virBufferAsprintf(&buf, "<selfctime>%llu</selfctime>\n",
                       (long long)virGetSelfLastChanged());
+    virBufferAsprintf(&buf, "<selfvers>%lu</selfvers>\n",
+                      (unsigned long)LIBVIR_VERSION_NUMBER);
 
     if (qemuCaps->usedQMP)
         virBufferAddLit(&buf, "<usedQMP/>\n");
@@ -2938,6 +2947,7 @@ virQEMUCapsInitCached(virQEMUCapsPtr qemuCaps, const char *cacheDir)
     struct stat sb;
     time_t qemuctime;
     time_t selfctime;
+    unsigned long selfvers;
 
     if (virAsprintf(&capsdir, "%s/capabilities", cacheDir) < 0)
         goto cleanup;
@@ -2970,7 +2980,8 @@ virQEMUCapsInitCached(virQEMUCapsPtr qemuCaps, const char *cacheDir)
         goto cleanup;
     }
 
-    if (virQEMUCapsLoadCache(qemuCaps, capsfile, &qemuctime, &selfctime) < 0) {
+    if (virQEMUCapsLoadCache(qemuCaps, capsfile, &qemuctime, &selfctime,
+                             &selfvers) < 0) {
         virErrorPtr err = virGetLastError();
         VIR_WARN("Failed to load cached caps from '%s' for '%s': %s",
                  capsfile, qemuCaps->binary, err ? NULLSTR(err->message) :
@@ -2983,12 +2994,14 @@ virQEMUCapsInitCached(virQEMUCapsPtr qemuCaps, const char *cacheDir)
 
     /* Discard cache if QEMU binary or libvirtd changed */
     if (qemuctime != qemuCaps->ctime ||
-        selfctime != virGetSelfLastChanged()) {
+        selfctime != virGetSelfLastChanged() ||
+        selfvers != LIBVIR_VERSION_NUMBER) {
         VIR_DEBUG("Outdated cached capabilities '%s' for '%s' "
-                  "(%lld vs %lld, %lld vs %lld)",
+                  "(%lld vs %lld, %lld vs %lld, %lu vs %lu)",
                   capsfile, qemuCaps->binary,
                   (long long)qemuctime, (long long)qemuCaps->ctime,
-                  (long long)selfctime, (long long)virGetSelfLastChanged());
+                  (long long)selfctime, (long long)virGetSelfLastChanged(),
+                  selfvers, (unsigned long)LIBVIR_VERSION_NUMBER);
         ignore_value(unlink(capsfile));
         virQEMUCapsReset(qemuCaps);
         ret = 0;