[PATCH 03/12] libxl: Earlier detection of not running on Xen

[Jim Fehlig <jfehlig@xxxxxxxx>]

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 th
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.

Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx>
---
 src/libxl/libxl_driver.c | 62 +++++++++++++++++++++++++++++++-----------------
 1 file changed, 40 insertions(+), 22 deletions(-)

diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c
index ff4f6be..759fed5 100644
--- a/src/libxl/libxl_driver.c
+++ b/src/libxl/libxl_driver.c
@@ -775,34 +775,54 @@ 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;
+    }
+
+    /* 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;
     }
 
-    /* Disable driver if legacy xen toolstack (xend) is in use */
+   /* 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;
 
@@ -883,21 +903,20 @@ 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;
+        VIR_ERROR(_("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;
+        VIR_ERROR(_("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;
+        VIR_ERROR(_("Failed to get version information from libxenlight"));
+        goto error;
     }
     libxl_driver->version = (ver_info->xen_version_major * 1000000) +
             (ver_info->xen_version_minor * 1000);
@@ -956,7 +975,6 @@ libxlStateInitialize(bool privileged,
 
 error:
     ret = -1;
-fail:
     VIR_FREE(log_file);
     if (libxl_driver)
         libxlDriverUnlock(libxl_driver);
-- 
1.8.1.4

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