wip

src/libostree/ostree-sysroot-cleanup.c

@@ -218,6 +218,7 @@ gboolean
 _ostree_sysroot_rmrf_deployment (OstreeSysroot *self, OstreeDeployment *deployment,
                                  GCancellable *cancellable, GError **error)
 {
+  g_autofree char *backing_relpath =_ostree_sysroot_get_deployment_backing_relpath (deployment);
   g_autofree char *origin_relpath = ostree_deployment_get_origin_relpath (deployment);
   g_autofree char *deployment_path = ostree_sysroot_get_deployment_dirpath (self, deployment);
   struct stat stbuf;
@@ -238,6 +239,12 @@ _ostree_sysroot_rmrf_deployment (OstreeSysroot *self, OstreeDeployment *deployme
   /* This deployment wasn't referenced, so delete it */
   if (!_ostree_linuxfs_fd_alter_immutable_flag (deployment_fd, FALSE, cancellable, error))
     return FALSE;
+  /* Note we must delete the origin and backing directories first, as the "source of truth"
+   * is the deployment path.  We don't currently have code that detects "orphaned"
+   * origin files or work directories.
+   */
+  if (!glnx_shutil_rm_rf_at (self->sysroot_fd, backing_relpath, cancellable, error))
+    return FALSE;
   if (!glnx_shutil_rm_rf_at (self->sysroot_fd, origin_relpath, cancellable, error))
     return FALSE;
   if (!glnx_shutil_rm_rf_at (self->sysroot_fd, deployment_path, cancellable, error))

src/libostree/ostree-sysroot-private.h

@@ -142,6 +142,8 @@ gboolean _ostree_sysroot_boot_complete (OstreeSysroot *self, GCancellable *cance
 
 OstreeDeployment *_ostree_sysroot_deserialize_deployment_from_variant (GVariant *v, GError **error);
 
+char *_ostree_sysroot_get_deployment_backing_relpath (OstreeDeployment *deployment);
+
 gboolean _ostree_sysroot_rmrf_deployment (OstreeSysroot *sysroot, OstreeDeployment *deployment,
                                           GCancellable *cancellable, GError **error);
 

src/libostree/ostree-sysroot.c

@@ -36,7 +36,7 @@
 #include "ostree-repo-private.h"
 #include "ostree-sepolicy-private.h"
 #include "ostree-sysroot-private.h"
-#include "ostree.h"
+#include "otcore.h"
 
 /**
  * SECTION:ostree-sysroot
@@ -1965,6 +1965,19 @@ ostree_sysroot_simple_write_deployment (OstreeSysroot *sysroot, const char *osna
   return TRUE;
 }
 
+/* Return the sysroot-relative path to the "backing" directory of a deployment
+ * which can hold additional data.
+ */
+char *
+_ostree_sysroot_get_deployment_backing_relpath (OstreeDeployment *deployment)
+{
+  return g_strdup_printf ("ostree/deploy/%s/deploy/%s.%d%s",
+                          ostree_deployment_get_osname (deployment), ostree_deployment_get_csum (deployment),
+                          ostree_deployment_get_deployserial (deployment),
+                          OSTREE_DEPLOYMENT_BACKING_EXT);
+}
+
+
 /* Deploy a copy of @target_deployment */
 static gboolean
 clone_deployment (OstreeSysroot *sysroot, OstreeDeployment *target_deployment,

src/libotcore/otcore.h

@@ -55,6 +55,9 @@ GKeyFile *otcore_load_config (int rootfs, const char *filename, GError **error);
 // we make it with mode 0 (which requires CAP_DAC_OVERRIDE to pass through).
 #define OTCORE_RUN_OSTREE_PRIVATE "/run/ostree/.private"
 
+// The directory holding extra/backing data for a deployment, such as overlayfs workdirs
+#define OSTREE_DEPLOYMENT_BACKING_EXT ".backing"
+
 // The name of the composefs metadata root
 #define OSTREE_COMPOSEFS_NAME ".ostree.cfs"
 // The temporary directory used for the EROFS mount; it's in the .private directory

src/switchroot/ostree-prepare-root.c

@@ -87,6 +87,8 @@
 #define SYSROOT_KEY "sysroot"
 #define READONLY_KEY "readonly"
 
+/* This key configures the / mount in the deployment root */
+#define ROOT_KEY "root"
 #define ETC_KEY "etc"
 #define TRANSIENT_KEY "transient"
 
@@ -352,6 +354,11 @@ main (int argc, char *argv[])
     errx (EXIT_FAILURE, "Failed to parse config: %s", error->message);
 
   gboolean sysroot_readonly = FALSE;
+  gboolean root_transient = FALSE;
+
+  if (!ot_keyfile_get_boolean_with_default (config, ROOT_KEY, TRANSIENT_KEY,
+                                            FALSE, &root_transient, &error))
+      return FALSE;
 
   // We always parse the composefs config, because we want to detect and error
   // out if it's enabled, but not supported at compile time.
@@ -375,6 +382,11 @@ main (int argc, char *argv[])
   if (root_mountpoint == NULL)
     err (EXIT_FAILURE, "realpath(\"%s\")", root_arg);
   g_autofree char *deploy_path = resolve_deploy_path (root_mountpoint);
+  const char *deploy_directory_name = glnx_basename (deploy_path);
+  // Note that realpath() should have stripped any trailing `/` which shouldn't
+  // be in the karg to start with, but we assert here to be sure we have a non-empty
+  // filename.
+  g_assert (deploy_directory_name && *deploy_directory_name);
 
   if (mkdirat (AT_FDCWD, OTCORE_RUN_OSTREE, 0755) < 0)
     err (EXIT_FAILURE, "Failed to create %s", OTCORE_RUN_OSTREE);
@@ -517,6 +529,30 @@ main (int argc, char *argv[])
         err (EXIT_FAILURE, "failed to make initial bind mount %s", deploy_path);
     }
 
+  if (root_transient)
+    {
+      const char *root_transient_dirname = "root-transient";
+      // Create the "backing" directory with additional data */
+      g_autofree char *backingdir = g_strdup_printf ("../%s%s", deploy_directory_name, OSTREE_DEPLOYMENT_BACKING_EXT);
+      if (!glnx_ensure_dir (AT_FDCWD, backingdir, 0700, &error))
+        err (EXIT_FAILURE, "%s", error->message);
+      // The root-transient holds overlayfs directories for the root
+      g_autofree char *rootovldir = g_build_filename (backingdir, root_transient_dirname, NULL);
+      if (!glnx_ensure_dir (AT_FDCWD, rootovldir, 0700, &error))
+        err (EXIT_FAILURE, "%s", error->message);
+      // Create the overlayfs upper
+      g_autofree char *upperdir = g_build_filename (backingdir, root_transient_dirname, "upper", NULL);
+      if (!glnx_ensure_dir (AT_FDCWD, upperdir, 0700, &error))
+        err (EXIT_FAILURE, "%s", error->message);
+      // And the overlayfs work
+      g_autofree char *workdir = g_build_filename (backingdir, root_transient_dirname, "work", NULL);
+      if (!glnx_ensure_dir (AT_FDCWD, workdir, 0700, &error))
+        err (EXIT_FAILURE, "%s", error->message);
+      g_autofree char *ovl_options = g_strdup_printf ("lowerdir=" TMP_SYSROOT ",upperdir=%s,workdir=%s", upperdir, workdir); 
+      if (mount ("overlay", ".", "overlay", MS_SILENT, ovl_options) < 0)
+        err (EXIT_FAILURE, "failed to mount transient root overlayfs");
+    }
+
   /* This will result in a system with /sysroot read-only. Thus, two additional
    * writable bind-mounts (for /etc and /var) are required later on. */
   if (sysroot_readonly)
@@ -548,7 +584,7 @@ main (int argc, char *argv[])
   /* Prepare /etc.
    * No action required if sysroot is writable. Otherwise, a bind-mount for
    * the deployment needs to be created and remounted as read/write. */
-  if (sysroot_readonly || using_composefs)
+  if (sysroot_readonly || using_composefs || root_transient)
     {
       gboolean etc_transient = FALSE;
       if (!ot_keyfile_get_boolean_with_default (config, ETC_KEY, TRANSIENT_KEY, FALSE,