qemu_cgroup: Allow /dev/mapper/control for PR

Just like in previous commit, qemu-pr-helper might want to open
/dev/mapper/control under certain circumstances. Therefore we
have to allow it in cgroups.

The change virdevmapper.c might look spurious but it isn't. After
6dd84f68 any path that we're allowing in deivces CGroup is
subject to virDevMapperGetTargets() inspection. And libdevmapper
returns ENXIO for the path from subject.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

src/qemu/qemu_cgroup.c

@@ -114,6 +114,8 @@ qemuSetupImagePathCgroup(virDomainObjPtr vm,
 }
 
 
+#define DEVICE_MAPPER_CONTROL_PATH "/dev/mapper/control"
+
 static int
 qemuSetupImageCgroupInternal(virDomainObjPtr vm,
                              virStorageSourcePtr src,
@@ -125,6 +127,10 @@ qemuSetupImageCgroupInternal(virDomainObjPtr vm,
         return 0;
     }
 
+    if (virStoragePRDefIsManaged(src->pr) &&
+        qemuSetupImagePathCgroup(vm, DEVICE_MAPPER_CONTROL_PATH, false) < 0)
+        return -1;
+
     return qemuSetupImagePathCgroup(vm, src->path, src->readonly || forceReadonly);
 }
 
@@ -142,9 +148,8 @@ qemuTeardownImageCgroup(virDomainObjPtr vm,
                         virStorageSourcePtr src)
 {
     qemuDomainObjPrivatePtr priv = vm->privateData;
-    int perms = VIR_CGROUP_DEVICE_READ |
-                VIR_CGROUP_DEVICE_WRITE |
-                VIR_CGROUP_DEVICE_MKNOD;
+    int perms = VIR_CGROUP_DEVICE_RWM;
+    size_t i;
     int ret;
 
     if (!virCgroupHasController(priv->cgroup,
@@ -157,6 +162,28 @@ qemuTeardownImageCgroup(virDomainObjPtr vm,
         return 0;
     }
 
+    for (i = 0; i < vm->def->ndisks; i++) {
+        virStorageSourcePtr diskSrc = vm->def->disks[i]->src;
+
+        if (src == diskSrc)
+            continue;
+
+        if (virStoragePRDefIsManaged(diskSrc->pr))
+            break;
+    }
+
+    if (i == vm->def->ndisks) {
+        VIR_DEBUG("Disabling device mapper control");
+        ret = virCgroupDenyDevicePath(priv->cgroup,
+                                      DEVICE_MAPPER_CONTROL_PATH, perms, true);
+        virDomainAuditCgroupPath(vm, priv->cgroup, "deny",
+                                 DEVICE_MAPPER_CONTROL_PATH,
+                                 virCgroupGetDevicePermsString(perms), ret);
+        if (ret < 0)
+            return ret;
+    }
+
+
     VIR_DEBUG("Deny path %s", src->path);
 
     ret = virCgroupDenyDevicePath(priv->cgroup, src->path, perms, true);

src/util/virdevmapper.c

@@ -101,8 +101,13 @@ virDevMapperGetTargetsImpl(const char *path,
 
     dm_task_no_open_count(dmt);
 
-    if (!dm_task_run(dmt))
+    if (!dm_task_run(dmt)) {
+        if (errno == ENXIO) {
+            /* If @path = "/dev/mapper/control" ENXIO is returned. */
+            ret = 0;
+        }
         goto cleanup;
+    }
 
     if (!dm_task_get_info(dmt, &info))
         goto cleanup;