qemu: Use namespaces iff available on the host kernel

So far the namespaces were turned on by default unconditionally.
For all non-Linux platforms we provided stub functions that just
ignored whatever namespaces setting there was in qemu.conf and
returned 0 to indicate success. Moreover, we didn't really check
if namespaces are available on the host kernel.

This is suboptimal as we might have ignored user setting.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_conf.c

@@ -317,8 +317,12 @@ virQEMUDriverConfigPtr virQEMUDriverConfigNew(bool privileged)
     if (!(cfg->namespaces = virBitmapNew(QEMU_DOMAIN_NS_LAST)))
         goto error;
 
-    if (virBitmapSetBit(cfg->namespaces, QEMU_DOMAIN_NS_MOUNT) < 0)
+#if defined(__linux__)
+    if (privileged &&
+        virProcessNamespaceAvailable(VIR_PROCESS_NAMESPACE_MNT) == 0 &&
+        virBitmapSetBit(cfg->namespaces, QEMU_DOMAIN_NS_MOUNT) < 0)
         goto error;
+#endif /* defined(__linux__) */
 
 #ifdef DEFAULT_LOADER_NVRAM
     if (virFirmwareParseList(DEFAULT_LOADER_NVRAM,

src/qemu/qemu_domain.c

@@ -6879,7 +6879,6 @@ qemuDomainGetHostdevPath(virDomainHostdevDefPtr dev,
 }
 
 
-#if defined(__linux__)
 /**
  * qemuDomainGetPreservedMounts:
  *
@@ -7432,12 +7431,20 @@ qemuDomainCreateNamespace(virQEMUDriverPtr driver,
     virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
     int ret = -1;
 
-    if (!virBitmapIsBitSet(cfg->namespaces, QEMU_DOMAIN_NS_MOUNT) ||
-        !virQEMUDriverIsPrivileged(driver)) {
+    if (!virBitmapIsBitSet(cfg->namespaces, QEMU_DOMAIN_NS_MOUNT)) {
         ret = 0;
         goto cleanup;
     }
 
+    if (!virQEMUDriverIsPrivileged(driver)) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                       _("cannot use namespaces in session mode"));
+        goto cleanup;
+    }
+
+    if (virProcessNamespaceAvailable(VIR_PROCESS_NAMESPACE_MNT) < 0)
+        goto cleanup;
+
     if (qemuDomainEnableNamespace(vm, QEMU_DOMAIN_NS_MOUNT) < 0)
         goto cleanup;
 
@@ -7447,28 +7454,6 @@ qemuDomainCreateNamespace(virQEMUDriverPtr driver,
     return ret;
 }
 
-#else /* !defined(__linux__) */
-
-int
-qemuDomainBuildNamespace(virQEMUDriverPtr driver ATTRIBUTE_UNUSED,
-                         virDomainObjPtr vm ATTRIBUTE_UNUSED)
-{
-    /* Namespaces are Linux specific. On other platforms just
-     * carry on with the old behaviour. */
-    return 0;
-}
-
-
-int
-qemuDomainCreateNamespace(virQEMUDriverPtr driver ATTRIBUTE_UNUSED,
-                          virDomainObjPtr vm ATTRIBUTE_UNUSED)
-{
-    /* Namespaces are Linux specific. On other platforms just
-     * carry on with the old behaviour. */
-    return 0;
-}
-#endif /* !defined(__linux__) */
-
 
 struct qemuDomainAttachDeviceMknodData {
     virQEMUDriverPtr driver;