lib/deploy: Add support for additional initrds

In FCOS and RHCOS, the need to configure software in the initramfs has
come up multiple times. Sometimes, using kernel arguments suffices.
Other times, it really must be a configuration file. Rebuilding the
initramfs on the client-side however is a costly operation. Not only
does it add complexity to the update workflow, it also erodes a lot of
the value obtained from using the baked "blessed" initramfs from the
tree itself.

One elegant way to address this is to allow specifying multiple
initramfses. This is supported by most bootloaders (notably GRUB) and
results in each initrd being checked out on top of each other.

This patch allows libostree clients to leverage this so that they can
avoid regenerating the initramfs entirely. libostree itself is agnostic
as to what kind and how much data overlay initrds contain. It's up to
the clients to enforce such boundaries.

To implement this, we add a new option to the deploy APIs called
`additional_initrds`: this is an array of filepaths to CPIO archives. We
copy these files into the bootcsum on `/boot` and add them to the BLS as
another `initrd` entry.

src/libostree/ostree-deployment-private.h

@@ -47,6 +47,7 @@ struct _OstreeDeployment
   char *csum;
   int deployserial;
   char *bootcsum;
+  char **additional_initrds;
   int bootserial;
   OstreeBootconfigParser *bootconfig;
   GKeyFile *origin;
@@ -56,4 +57,9 @@ struct _OstreeDeployment
 
 void _ostree_deployment_set_bootcsum (OstreeDeployment *self, const char *bootcsum);
 
+void _ostree_deployment_set_additional_initrds (OstreeDeployment *self,
+                                                char **additional_initrds);
+char**
+_ostree_deployment_get_additional_initrds (OstreeDeployment *self);
+
 G_END_DECLS

src/libostree/ostree-deployment.c

@@ -158,6 +158,20 @@ _ostree_deployment_set_bootcsum (OstreeDeployment *self,
   self->bootcsum = g_strdup (bootcsum);
 }
 
+void
+_ostree_deployment_set_additional_initrds (OstreeDeployment *self,
+                                           char            **additional_initrds)
+{
+  g_strfreev (self->additional_initrds);
+  self->additional_initrds = g_strdupv (additional_initrds);
+}
+
+char**
+_ostree_deployment_get_additional_initrds (OstreeDeployment *self)
+{
+  return self->additional_initrds;
+}
+
 /**
  * ostree_deployment_clone:
  * @self: Deployment
@@ -238,6 +252,7 @@ ostree_deployment_finalize (GObject *object)
   g_free (self->bootcsum);
   g_clear_object (&self->bootconfig);
   g_clear_pointer (&self->origin, g_key_file_unref);
+  g_strfreev (self->additional_initrds);
 
   G_OBJECT_CLASS (ostree_deployment_parent_class)->finalize (object);
 }

src/libostree/ostree-sysroot-deploy.c

@@ -1859,6 +1859,42 @@ install_deployment_kernel (OstreeSysroot   *sysroot,
         }
     }
 
+  g_autoptr(GPtrArray) additional_initrds = NULL;
+  for (char **it = _ostree_deployment_get_additional_initrds (deployment); it && *it; it++)
+    {
+      char *initrd = *it;
+
+      /* Additional initrds are not part of the bootcsum; they're not part of the tree
+       * proper. But they're named by their csum. Doing it this way allows sharing the same
+       * bootcsum dir for multiple deployments with the only change being in additional
+       * initrds. The downside is that we would need to implement our own GC based on
+       * referenced overlays from all the bootconfigs; that said, they're tiny overlays and
+       * will get blown away on each kernel/initrd update. */
+
+      g_autofree char *checksum =
+        ot_checksum_file_at (AT_FDCWD, initrd, G_CHECKSUM_SHA256, cancellable, error);
+      if (checksum == NULL)
+        return glnx_prefix_error (error, "Checksumming %s", initrd);
+
+      g_autofree char *destpath =
+        g_strdup_printf ("/%s/initramfs-overlay-%s.img", bootcsumdir, checksum);
+
+      const char *base_destpath = glnx_basename (destpath);
+      if (!glnx_fstatat_allow_noent (bootcsum_dfd, base_destpath, &stbuf, 0, error))
+        return FALSE;
+
+      if (errno == ENOENT)
+        {
+          if (!install_into_boot (repo, sepolicy, AT_FDCWD, initrd, bootcsum_dfd,
+                                  base_destpath, sysroot->debug_flags, cancellable, error))
+            return FALSE;
+        }
+
+      if (additional_initrds == NULL)
+        additional_initrds = g_ptr_array_new_with_free_func (g_free);
+      g_ptr_array_add (additional_initrds, g_steal_pointer (&destpath));
+    }
+
   g_autofree char *contents = NULL;
   if (!glnx_fstatat_allow_noent (deployment_dfd, "usr/lib/os-release", &stbuf, 0, error))
     return FALSE;
@@ -1938,6 +1974,12 @@ install_deployment_kernel (OstreeSysroot   *sysroot,
       g_autofree char * initrd_boot_relpath =
         g_strconcat ("/", bootcsumdir, "/", kernel_layout->initramfs_namever, NULL);
       ostree_bootconfig_parser_set (bootconfig, "initrd", initrd_boot_relpath);
+
+      if (additional_initrds)
+        {
+          for (guint i = 0; i < additional_initrds->len; i++)
+            ostree_bootconfig_parser_add_initrd (bootconfig, additional_initrds->pdata[i]);
+        }
     }
   else
     {
@@ -2716,6 +2758,7 @@ sysroot_initialize_deployment (OstreeSysroot     *self,
 
   _ostree_deployment_set_bootcsum (new_deployment, kernel_layout->bootcsum);
   _ostree_deployment_set_bootconfig_from_kargs (new_deployment, opts->override_kernel_argv);
+  _ostree_deployment_set_additional_initrds (new_deployment, opts->additional_initrds);
 
   if (!prepare_deployment_etc (self, repo, new_deployment, deployment_dfd,
                                cancellable, error))
@@ -3116,6 +3159,9 @@ ostree_sysroot_stage_tree_with_options (OstreeSysroot     *self,
   if (opts->override_kernel_argv)
     g_variant_builder_add (builder, "{sv}", "kargs",
                            g_variant_new_strv ((const char *const*)opts->override_kernel_argv, -1));
+  if (opts->additional_initrds)
+    g_variant_builder_add (builder, "{sv}", "additional-initrds",
+                           g_variant_new_strv ((const char *const*)opts->additional_initrds, -1));
 
   const char *parent = dirname (strdupa (_OSTREE_SYSROOT_RUNSTATE_STAGED));
   if (!glnx_shutil_mkdir_p_at (AT_FDCWD, parent, 0755, cancellable, error))

src/libostree/ostree-sysroot.c

@@ -966,8 +966,10 @@ _ostree_sysroot_reload_staged (OstreeSysroot *self,
       /* Parse it */
       g_autoptr(GVariant) target = NULL;
       g_autofree char **kargs = NULL;
+      g_autofree char **additional_initrds = NULL;
       g_variant_dict_lookup (staged_deployment_dict, "target", "@a{sv}", &target);
       g_variant_dict_lookup (staged_deployment_dict, "kargs", "^a&s", &kargs);
+      g_variant_dict_lookup (staged_deployment_dict, "additional-initrds", "^a&s", &additional_initrds);
       if (target)
         {
           g_autoptr(OstreeDeployment) staged =
@@ -979,6 +981,8 @@ _ostree_sysroot_reload_staged (OstreeSysroot *self,
           if (!load_origin (self, staged, NULL, error))
             return FALSE;
 
+          _ostree_deployment_set_additional_initrds (staged, additional_initrds);
+
           self->staged_deployment = g_steal_pointer (&staged);
           self->staged_deployment_data = g_steal_pointer (&staged_deployment_data);
           /* We set this flag for ostree_deployment_is_staged() because that API

src/libostree/ostree-sysroot.h

@@ -190,7 +190,8 @@ typedef struct {
   gboolean unused_bools[8];
   int unused_ints[8];
   char **override_kernel_argv;
-  gpointer unused_ptrs[7];
+  char **additional_initrds;
+  gpointer unused_ptrs[6];
 } OstreeSysrootDeployTreeOpts;
 
 _OSTREE_PUBLIC