Auto-add a root <filesystem> element to LXC containers on startup

Currently the LXC container code has two codepaths, depending on
whether there is a <filesystem> element with a target path of '/'.
If we automatically add a <filesystem> device with src=/ and dst=/,
for any container which has not specified a root filesystem, then
we only need one codepath for setting up the filesystem.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/lxc/lxc_container.c

@@ -2049,92 +2049,6 @@ cleanup:
 }
 
 
-/* Nothing mapped to /, we're using the main root,
-   but with extra stuff mapped in */
-static int lxcContainerSetupExtraMounts(virDomainDefPtr vmDef,
-                                        virDomainFSDefPtr root,
-                                        virSecurityManagerPtr securityDriver)
-{
-    int ret = -1;
-    struct lxcContainerCGroup *mounts = NULL;
-    size_t nmounts = 0;
-    char *cgroupRoot = NULL;
-    char *sec_mount_options;
-
-    VIR_DEBUG("def=%p", vmDef);
-
-    if (!(sec_mount_options = virSecurityManagerGetMountOptions(securityDriver, vmDef)))
-        return -1;
-
-    /*
-     * This makes sure that any new filesystems in the
-     * host OS propagate to the container, but any
-     * changes in the container are private
-     */
-    if (mount("", "/", NULL, MS_SLAVE|MS_REC, NULL) < 0) {
-        virReportSystemError(errno, "%s",
-                             _("Failed to make / slave"));
-        goto cleanup;
-    }
-
-    if (root && root->readonly) {
-        if (mount("", "/", NULL, MS_BIND|MS_REC|MS_RDONLY|MS_REMOUNT, NULL) < 0) {
-            virReportSystemError(errno, "%s",
-                                 _("Failed to make root readonly"));
-            goto cleanup;
-        }
-    }
-
-    VIR_DEBUG("Mounting config FS");
-    if (lxcContainerMountAllFS(vmDef, "", false, sec_mount_options) < 0)
-        goto cleanup;
-
-    /* Before replacing /sys we need to identify any
-     * cgroups controllers that are mounted */
-    if (lxcContainerIdentifyCGroups(&mounts, &nmounts, &cgroupRoot) < 0)
-        goto cleanup;
-
-#if WITH_SELINUX
-    /* Some versions of Linux kernel don't let you overmount
-     * the selinux filesystem, so make sure we kill it first
-     */
-    if (lxcContainerUnmountSubtree(SELINUX_MOUNT, false) < 0)
-        goto cleanup;
-#endif
-
-    /* Gets rid of any existing stuff under /proc, since we need new
-     * namespace aware versions of those. We must do /proc second
-     * otherwise we won't find /proc/mounts :-) */
-    if (lxcContainerUnmountSubtree("/sys", false) < 0 ||
-        lxcContainerUnmountSubtree("/proc", false) < 0)
-        goto cleanup;
-
-    /* Mounts the core /proc, /sys, etc filesystems */
-    if (lxcContainerMountBasicFS(false, sec_mount_options) < 0)
-        goto cleanup;
-
-    /* Mounts /proc/meminfo etc sysinfo */
-    if (lxcContainerMountProcFuse(vmDef, NULL) < 0)
-        goto cleanup;
-
-    /* Now we can re-mount the cgroups controllers in the
-     * same configuration as before */
-    if (lxcContainerMountCGroups(mounts, nmounts,
-                                 cgroupRoot, sec_mount_options) < 0)
-        goto cleanup;
-
-    VIR_DEBUG("Mounting completed");
-
-    ret = 0;
-
-cleanup:
-    lxcContainerCGroupFree(mounts, nmounts);
-    VIR_FREE(cgroupRoot);
-    VIR_FREE(sec_mount_options);
-    return ret;
-}
-
-
 static int lxcContainerResolveSymlinks(virDomainDefPtr vmDef)
 {
     char *newroot;
@@ -2156,24 +2070,6 @@ static int lxcContainerResolveSymlinks(virDomainDefPtr vmDef)
     return 0;
 }
 
-static int lxcContainerSetupMounts(virDomainDefPtr vmDef,
-                                   virDomainFSDefPtr root,
-                                   char **ttyPaths,
-                                   size_t nttyPaths,
-                                   virSecurityManagerPtr securityDriver)
-{
-    if (lxcContainerResolveSymlinks(vmDef) < 0)
-        return -1;
-
-    if (root && root->src)
-        return  lxcContainerSetupPivotRoot(vmDef, root, ttyPaths, nttyPaths,
-                                           securityDriver);
-    else
-        return lxcContainerSetupExtraMounts(vmDef, root,
-                                            securityDriver);
-}
-
-
 /*
  * This is running as the 'init' process insid the container.
  * It removes some capabilities that could be dangerous to
@@ -2290,9 +2186,12 @@ static int lxcContainerChild(void *data)
         goto cleanup;
     }
 
-    if (lxcContainerSetupMounts(vmDef, root,
-                                argv->ttyPaths, argv->nttyPaths,
-                                argv->securityDriver) < 0)
+    if (lxcContainerResolveSymlinks(vmDef) < 0)
+        goto cleanup;
+
+    if (lxcContainerSetupPivotRoot(vmDef, root,
+                                   argv->ttyPaths, argv->nttyPaths,
+                                   argv->securityDriver) < 0)
         goto cleanup;
 
     if (!virFileExists(vmDef->os.init)) {

src/lxc/lxc_process.c

@@ -981,6 +981,38 @@ virLXCProcessReadLogOutput(virDomainObjPtr vm,
     return ret;
 }
 
+
+static int
+virLXCProcessEnsureRootFS(virDomainObjPtr vm)
+{
+    virDomainFSDefPtr root = virDomainGetRootFilesystem(vm->def);
+
+    if (root)
+        return 0;
+
+    if (VIR_ALLOC(root) < 0)
+        goto no_memory;
+
+    root->type = VIR_DOMAIN_FS_TYPE_MOUNT;
+
+    if (!(root->src = strdup("/")) ||
+        !(root->dst = strdup("/")))
+        goto no_memory;
+
+    if (VIR_INSERT_ELEMENT(vm->def->fss,
+                           0,
+                           vm->def->nfss,
+                           root) < 0)
+        goto no_memory;
+
+    return 0;
+
+no_memory:
+    virReportOOMError();
+    virDomainFSDefFree(root);
+    return -1;
+}
+
 /**
  * virLXCProcessStart:
  * @conn: pointer to connection
@@ -1078,6 +1110,9 @@ int virLXCProcessStart(virConnectPtr conn,
             goto cleanup;
     }
 
+    if (virLXCProcessEnsureRootFS(vm) < 0)
+        goto cleanup;
+
     /* Must be run before security labelling */
     VIR_DEBUG("Preparing host devices");
     if (virLXCPrepareHostDevices(driver, vm->def) < 0)