libxl: Earlier detection of not running on Xen

Detect early on in libxl driver initialization if the driver
should be loaded at all, avoiding needless initialization steps
that only have to be undone later.  While at it, move the
detection to a helper function to improve readability.

After detecting that the driver should be loaded, subsequent
failures such as initializing the log stream, allocating libxl
ctx, etc. should be treated as failure to initialize the driver.

src/libxl/libxl_driver.c

@@ -775,39 +775,60 @@ libxlStateCleanup(void)
     return 0;
 }
 
-static int
-libxlStateInitialize(bool privileged,
-                     virStateInhibitCallback callback ATTRIBUTE_UNUSED,
-                     void *opaque ATTRIBUTE_UNUSED)
+static bool
+libxlDriverShouldLoad(bool privileged)
 {
-    const libxl_version_info *ver_info;
-    char *log_file = NULL;
+    bool ret = false;
     virCommandPtr cmd;
-    int status, ret = 0;
-    unsigned int free_mem;
-    char ebuf[1024];
+    int status;
 
-    /* Disable libxl driver if non-root */
+    /* Don't load if non-root */
     if (!privileged) {
         VIR_INFO("Not running privileged, disabling libxenlight driver");
-        return 0;
+        return ret;
     }
 
-    /* Disable driver if legacy xen toolstack (xend) is in use */
+    /* Don't load if not running on a Xen control domain (dom0) */
+    if (!virFileExists("/proc/xen/capabilities")) {
+        VIR_INFO("No Xen capabilities detected, probably not running "
+                 "in a Xen Dom0.  Disabling libxenlight driver");
+
+        return ret;
+    }
+
+    /* Don't load if legacy xen toolstack (xend) is in use */
     cmd = virCommandNewArgList("/usr/sbin/xend", "status", NULL);
     if (virCommandRun(cmd, &status) == 0 && status == 0) {
         VIR_INFO("Legacy xen tool stack seems to be in use, disabling "
                   "libxenlight driver.");
-        virCommandFree(cmd);
-        return 0;
+    } else {
+        ret = true;
     }
     virCommandFree(cmd);
 
+    return ret;
+}
+
+static int
+libxlStateInitialize(bool privileged,
+                     virStateInhibitCallback callback ATTRIBUTE_UNUSED,
+                     void *opaque ATTRIBUTE_UNUSED)
+{
+    const libxl_version_info *ver_info;
+    char *log_file = NULL;
+    int ret = 0;
+    unsigned int free_mem;
+    char ebuf[1024];
+
+    if (!libxlDriverShouldLoad(privileged))
+        return 0;
+
     if (VIR_ALLOC(libxl_driver) < 0)
         return -1;
 
     if (virMutexInit(&libxl_driver->lock) < 0) {
-        VIR_ERROR(_("cannot initialize mutex"));
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       "%s", _("cannot initialize mutex"));
         VIR_FREE(libxl_driver);
         return -1;
     }
@@ -841,23 +862,31 @@ libxlStateInitialize(bool privileged,
         goto error;
 
     if (virFileMakePath(libxl_driver->logDir) < 0) {
-        VIR_ERROR(_("Failed to create log dir '%s': %s"),
-                  libxl_driver->logDir, virStrerror(errno, ebuf, sizeof(ebuf)));
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("failed to create log dir '%s': %s"),
+                       libxl_driver->logDir,
+                       virStrerror(errno, ebuf, sizeof(ebuf)));
         goto error;
     }
     if (virFileMakePath(libxl_driver->stateDir) < 0) {
-        VIR_ERROR(_("Failed to create state dir '%s': %s"),
-                  libxl_driver->stateDir, virStrerror(errno, ebuf, sizeof(ebuf)));
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("failed to create state dir '%s': %s"),
+                       libxl_driver->stateDir,
+                       virStrerror(errno, ebuf, sizeof(ebuf)));
         goto error;
     }
     if (virFileMakePath(libxl_driver->libDir) < 0) {
-        VIR_ERROR(_("Failed to create lib dir '%s': %s"),
-                  libxl_driver->libDir, virStrerror(errno, ebuf, sizeof(ebuf)));
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("failed to create lib dir '%s': %s"),
+                       libxl_driver->libDir,
+                       virStrerror(errno, ebuf, sizeof(ebuf)));
         goto error;
     }
     if (virFileMakePath(libxl_driver->saveDir) < 0) {
-        VIR_ERROR(_("Failed to create save dir '%s': %s"),
-                  libxl_driver->saveDir, virStrerror(errno, ebuf, sizeof(ebuf)));
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("failed to create save dir '%s': %s"),
+                       libxl_driver->saveDir,
+                       virStrerror(errno, ebuf, sizeof(ebuf)));
         goto error;
     }
 
@@ -883,28 +912,32 @@ libxlStateInitialize(bool privileged,
     libxl_driver->logger =
             (xentoollog_logger *)xtl_createlogger_stdiostream(libxl_driver->logger_file, XTL_DEBUG, 0);
     if (!libxl_driver->logger) {
-        VIR_INFO("cannot create logger for libxenlight, disabling driver");
-        goto fail;
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       "%s", _("failed to create logger for libxenlight"));
+        goto error;
     }
 
     if (libxl_ctx_alloc(&libxl_driver->ctx,
                        LIBXL_VERSION, 0,
                        libxl_driver->logger)) {
-        VIR_INFO("cannot initialize libxenlight context, probably not running "
-                 "in a Xen Dom0, disabling driver");
-        goto fail;
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       "%s", _("failed to initialize libxenlight context"));
+        goto error;
     }
 
     if ((ver_info = libxl_get_version_info(libxl_driver->ctx)) == NULL) {
-        VIR_INFO("cannot version information from libxenlight, disabling driver");
-        goto fail;
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       "%s",
+                       _("failed to get version information from libxenlight"));
+        goto error;
     }
     libxl_driver->version = (ver_info->xen_version_major * 1000000) +
             (ver_info->xen_version_minor * 1000);
 
     if ((libxl_driver->caps =
          libxlMakeCapabilities(libxl_driver->ctx)) == NULL) {
-        VIR_ERROR(_("cannot create capabilities for libxenlight"));
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       "%s", _("cannot create capabilities for libxenlight"));
         goto error;
     }
 
@@ -916,7 +949,10 @@ libxlStateInitialize(bool privileged,
     /* This will fill xenstore info about free and dom0 memory if missing,
      * should be called before starting first domain */
     if (libxl_get_free_memory(libxl_driver->ctx, &free_mem)) {
-        VIR_ERROR(_("Unable to configure libxl's memory management parameters"));
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       "%s",
+                       _("Unable to configure libxl's memory management "
+                         "parameters"));
         goto error;
     }
 
@@ -956,7 +992,6 @@ libxlStateInitialize(bool privileged,
 
 error:
     ret = -1;
-fail:
     VIR_FREE(log_file);
     if (libxl_driver)
         libxlDriverUnlock(libxl_driver);