qemu: implement persistent file cache for nbdkit caps

Implement the loadFile and saveFile virFileCacheHandlers callbacks so
that nbdkit capabilities are cached perstistently across daemon
restarts. The format and implementation is modeled on the qemu
capabilities, but simplified slightly.

Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>

po/POTFILES

@@ -181,6 +181,7 @@ src/qemu/qemu_monitor.c
 src/qemu/qemu_monitor_json.c
 src/qemu/qemu_monitor_text.c
 src/qemu/qemu_namespace.c
+src/qemu/qemu_nbdkit.c
 src/qemu/qemu_passt.c
 src/qemu/qemu_process.c
 src/qemu/qemu_qapi.c

src/qemu/qemu_nbdkit.c

@@ -312,11 +312,233 @@ virNbdkitCapsNewData(const char *binary,
 }
 
 
+static int
+qemuNbdkitCapsValidateBinary(qemuNbdkitCaps *nbdkitCaps,
+                             xmlXPathContextPtr ctxt)
+{
+    g_autofree char *str = NULL;
+
+    if (!(str = virXPathString("string(./path)", ctxt))) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("missing path in nbdkit capabilities cache"));
+        return -1;
+    }
+
+    if (STRNEQ(str, nbdkitCaps->path)) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("Expected caps for '%1$s' but saw '%2$s'"),
+                       nbdkitCaps->path, str);
+        return -1;
+    }
+
+    return 0;
+}
+
+
+static int
+qemuNbdkitCapsParseFlags(qemuNbdkitCaps *nbdkitCaps,
+                         xmlXPathContextPtr ctxt)
+{
+    g_autofree xmlNodePtr *nodes = NULL;
+    size_t i;
+    int n;
+
+    if ((n = virXPathNodeSet("./flag", ctxt, &nodes)) < 0) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("failed to parse qemu capabilities flags"));
+        return -1;
+    }
+
+    VIR_DEBUG("Got flags %d", n);
+    for (i = 0; i < n; i++) {
+        unsigned int flag;
+
+        if (virXMLPropEnum(nodes[i], "name", qemuNbdkitCapsTypeFromString,
+                           VIR_XML_PROP_REQUIRED, &flag) < 0)
+            return -1;
+
+        qemuNbdkitCapsSet(nbdkitCaps, flag);
+    }
+
+    return 0;
+}
+
+
+/*
+ * Parsing a doc that looks like
+ *
+ * <nbdkitCaps>
+ *   <path>/some/path</path>
+ *   <nbdkitctime>234235253</nbdkitctime>
+ *   <plugindirmtime>234235253</plugindirmtime>
+ *   <filterdirmtime>234235253</filterdirmtime>
+ *   <selfctime>234235253</selfctime>
+ *   <selfvers>1002016</selfvers>
+ *   <flag name='foo'/>
+ *   <flag name='bar'/>
+ *   ...
+ * </nbdkitCaps>
+ *
+ * Returns 0 on success, 1 if outdated, -1 on error
+ */
+static int
+qemuNbdkitCapsLoadCache(qemuNbdkitCaps *nbdkitCaps,
+                        const char *filename)
+{
+    g_autoptr(xmlDoc) doc = NULL;
+    g_autoptr(xmlXPathContext) ctxt = NULL;
+    long long int l;
+
+    if (!(doc = virXMLParse(filename, NULL, NULL, "nbdkitCaps", &ctxt, NULL, false)))
+        return -1;
+
+    if (virXPathLongLong("string(./selfctime)", ctxt, &l) < 0) {
+        VIR_DEBUG("missing selfctime in nbdkit capabilities XML");
+        return -1;
+    }
+    nbdkitCaps->libvirtCtime = (time_t)l;
+
+    nbdkitCaps->libvirtVersion = 0;
+    virXPathUInt("string(./selfvers)", ctxt, &nbdkitCaps->libvirtVersion);
+
+    if (nbdkitCaps->libvirtCtime != virGetSelfLastChanged() ||
+        nbdkitCaps->libvirtVersion != LIBVIR_VERSION_NUMBER) {
+        VIR_DEBUG("Outdated capabilities in %s: libvirt changed (%lld vs %lld, %lu vs %lu), stopping load",
+                  nbdkitCaps->path,
+                  (long long)nbdkitCaps->libvirtCtime,
+                  (long long)virGetSelfLastChanged(),
+                  (unsigned long)nbdkitCaps->libvirtVersion,
+                  (unsigned long)LIBVIR_VERSION_NUMBER);
+        return 1;
+    }
+
+    if (qemuNbdkitCapsValidateBinary(nbdkitCaps, ctxt) < 0)
+        return -1;
+
+    if (virXPathLongLong("string(./nbdkitctime)", ctxt, &l) < 0) {
+        VIR_DEBUG("missing nbdkitctime in nbdkit capabilities XML");
+        return -1;
+    }
+    nbdkitCaps->ctime = (time_t)l;
+
+    if (virXPathLongLong("string(./plugindirmtime)", ctxt, &l) < 0) {
+        VIR_DEBUG("missing plugindirmtime in nbdkit capabilities XML");
+        return -1;
+    }
+    nbdkitCaps->pluginDirMtime = (time_t)l;
+
+    if (virXPathLongLong("string(./filterdirmtime)", ctxt, &l) < 0) {
+        VIR_DEBUG("missing filterdirmtime in nbdkit capabilities XML");
+        return -1;
+    }
+    nbdkitCaps->filterDirMtime = (time_t)l;
+
+    if (qemuNbdkitCapsParseFlags(nbdkitCaps, ctxt) < 0)
+        return -1;
+
+    if ((nbdkitCaps->version = virXPathString("string(./version)", ctxt)) == NULL) {
+        VIR_DEBUG("missing version in nbdkit capabilities cache");
+        return -1;
+    }
+
+    return 0;
+}
+
+
+static void*
+virNbdkitCapsLoadFile(const char *filename,
+                      const char *binary,
+                      void *privData G_GNUC_UNUSED,
+                      bool *outdated)
+{
+    g_autoptr(qemuNbdkitCaps) nbdkitCaps = qemuNbdkitCapsNew(binary);
+    int ret;
+
+    if (!nbdkitCaps)
+        return NULL;
+
+    ret = qemuNbdkitCapsLoadCache(nbdkitCaps, filename);
+    if (ret < 0)
+        return NULL;
+    if (ret == 1) {
+        *outdated = true;
+        return NULL;
+    }
+
+    return g_steal_pointer(&nbdkitCaps);
+}
+
+
+static char*
+qemuNbdkitCapsFormatCache(qemuNbdkitCaps *nbdkitCaps)
+{
+    g_auto(virBuffer) buf = VIR_BUFFER_INITIALIZER;
+    size_t i;
+
+    virBufferAddLit(&buf, "<nbdkitCaps>\n");
+    virBufferAdjustIndent(&buf, 2);
+
+    virBufferEscapeString(&buf, "<path>%s</path>\n",
+                          nbdkitCaps->path);
+    virBufferAsprintf(&buf, "<nbdkitctime>%lu</nbdkitctime>\n",
+                      nbdkitCaps->ctime);
+    virBufferAsprintf(&buf, "<plugindirmtime>%lu</plugindirmtime>\n",
+                      nbdkitCaps->pluginDirMtime);
+    virBufferAsprintf(&buf, "<filterdirmtime>%lu</filterdirmtime>\n",
+                      nbdkitCaps->filterDirMtime);
+    virBufferAsprintf(&buf, "<selfctime>%lu</selfctime>\n",
+                      nbdkitCaps->libvirtCtime);
+    virBufferAsprintf(&buf, "<selfvers>%u</selfvers>\n",
+                      nbdkitCaps->libvirtVersion);
+
+    for (i = 0; i < QEMU_NBDKIT_CAPS_LAST; i++) {
+        if (qemuNbdkitCapsGet(nbdkitCaps, i)) {
+            virBufferAsprintf(&buf, "<flag name='%s'/>\n",
+                              qemuNbdkitCapsTypeToString(i));
+        }
+    }
+
+    virBufferAsprintf(&buf, "<version>%s</version>\n",
+                      nbdkitCaps->version);
+
+    virBufferAdjustIndent(&buf, -2);
+    virBufferAddLit(&buf, "</nbdkitCaps>\n");
+
+    return virBufferContentAndReset(&buf);
+}
+
+
+static int
+virNbdkitCapsSaveFile(void *data,
+                      const char *filename,
+                      void *privData G_GNUC_UNUSED)
+{
+    qemuNbdkitCaps *nbdkitCaps = data;
+    g_autofree char *xml = NULL;
+
+    xml = qemuNbdkitCapsFormatCache(nbdkitCaps);
+
+    if (virFileWriteStr(filename, xml, 0600) < 0) {
+        virReportSystemError(errno,
+                             _("Failed to save '%1$s' for '%2$s'"),
+                             filename, nbdkitCaps->path);
+        return -1;
+    }
+
+    VIR_DEBUG("Saved caps '%s' for '%s' with (%lu, %lu)",
+              filename, nbdkitCaps->path,
+              nbdkitCaps->ctime,
+              nbdkitCaps->libvirtCtime);
+
+    return 0;
+}
+
+
 virFileCacheHandlers nbdkitCapsCacheHandlers = {
     .isValid = virNbdkitCapsIsValid,
     .newData = virNbdkitCapsNewData,
-    .loadFile = NULL,
-    .saveFile = NULL,
+    .loadFile = virNbdkitCapsLoadFile,
+    .saveFile = virNbdkitCapsSaveFile,
     .privFree = NULL,
 };