Add sysroot.bootloader repo config key

The sysroot.bootloader key configures the bootloader
that OSTree uses when deploying a sysroot. Having this key
allows specifying behavior not to use the default bootloader
backend code, which is preferable when creating a first
deployment from the sysroot (#1774).

As of now, the key can take the values "auto" or "none". If
the key is not given, the value defaults to "auto".

"auto" causes _ostree_sysroot_query_bootloader() to be used
when writing a new deployment, which is the original behavior
that dynamically detects which bootloader to use.

"none" avoids querying the bootloader dynamically. The BLS
config fragments are still written to
sysroot/boot/loader/entries for use by higher-level software.

More values can be supported in future to specify a single
bootloader, different behavior for the bootloader code, or
a list of bootloaders to try.

Resolves: #1774

Closes: #1814
Approved by: jlebon

src/libostree/ostree-repo-private.h

@@ -169,6 +169,7 @@ struct OstreeRepo {
   guint64 payload_link_threshold;
   gint fs_support_reflink; /* The underlying filesystem has support for ioctl (FICLONE..) */
   gchar **repo_finders;
+  gchar *bootloader; /* Configure which bootloader to use. */
 
   OstreeRepo *parent_repo;
 };

src/libostree/ostree-repo.c

@@ -3113,6 +3113,32 @@ reload_remote_config (OstreeRepo          *self,
   return TRUE;
 }
 
+static gboolean
+reload_sysroot_config (OstreeRepo          *self,
+                       GCancellable        *cancellable,
+                       GError             **error)
+{
+  { g_autofree char *bootloader = NULL;
+
+    if (!ot_keyfile_get_value_with_default_group_optional (self->config, "sysroot",
+                                                           "bootloader", "auto",
+                                                           &bootloader, error))
+      return FALSE;
+
+    /* TODO: possibly later add support for specifying a generic bootloader
+     * binary "x" in /usr/lib/ostree/bootloaders/x). See:
+     * https://github.com/ostreedev/ostree/issues/1719
+     * https://github.com/ostreedev/ostree/issues/1801
+     */
+    if (!(g_str_equal (bootloader, "auto") || g_str_equal (bootloader, "none")))
+      return glnx_throw (error, "Invalid bootloader configuration: '%s'", bootloader);
+
+    self->bootloader = g_steal_pointer (&bootloader);
+  }
+
+  return TRUE;
+}
+
 /**
  * ostree_repo_reload_config:
  * @self: repo
@@ -3131,6 +3157,8 @@ ostree_repo_reload_config (OstreeRepo          *self,
     return FALSE;
   if (!reload_remote_config (self, cancellable, error))
     return FALSE;
+  if (!reload_sysroot_config (self, cancellable, error))
+    return FALSE;
   return TRUE;
 }
 
@@ -6064,3 +6092,21 @@ ostree_repo_get_default_repo_finders (OstreeRepo *self)
 
   return (const gchar * const *)self->repo_finders;
 }
+
+/**
+ * ostree_repo_get_bootloader:
+ * @self: an #OstreeRepo
+ * 
+ * Get the bootloader configured. See the documentation for the
+ * "sysroot.bootloader" config key.
+ * 
+ * Returns: bootloader configuration for the sysroot
+ * Since: 2019.2
+ */
+const gchar *
+ostree_repo_get_bootloader (OstreeRepo   *self)
+{
+  g_return_val_if_fail (OSTREE_IS_REPO (self), NULL);
+
+  return self->bootloader;
+}

src/libostree/ostree-repo.h

@@ -115,6 +115,9 @@ gboolean      ostree_repo_set_collection_id (OstreeRepo   *self,
 _OSTREE_PUBLIC
 const gchar * const * ostree_repo_get_default_repo_finders (OstreeRepo   *self);
 
+_OSTREE_PUBLIC
+const gchar * ostree_repo_get_bootloader (OstreeRepo   *self);
+
 _OSTREE_PUBLIC
 GFile *       ostree_repo_get_path (OstreeRepo  *self);
 

src/libostree/ostree-sysroot-deploy.c

@@ -2310,6 +2310,7 @@ ostree_sysroot_write_deployments_with_options (OstreeSysroot     *self,
   gboolean bootloader_is_atomic = FALSE;
   SyncStats syncstats = { 0, };
   g_autoptr(OstreeBootloader) bootloader = NULL;
+  const char *bootloader_config = NULL;
   if (!requires_new_bootversion)
     {
       if (!create_new_bootlinks (self, self->bootversion,
@@ -2342,8 +2343,22 @@ ostree_sysroot_write_deployments_with_options (OstreeSysroot     *self,
             return glnx_throw_errno_prefix (error, "Remounting /boot read-write");
         }
 
-      if (!_ostree_sysroot_query_bootloader (self, &bootloader, cancellable, error))
-        return FALSE;
+      OstreeRepo *repo = ostree_sysroot_repo (self);
+
+      bootloader_config = ostree_repo_get_bootloader (repo);
+
+      g_debug ("Using bootloader configuration: %s", bootloader_config);
+
+      if (g_str_equal (bootloader_config, "auto"))
+        {
+          if (!_ostree_sysroot_query_bootloader (self, &bootloader, cancellable, error))
+            return FALSE;
+        }
+      else if (g_str_equal (bootloader_config, "none"))
+        {
+          /* No bootloader specified; do not query bootloaders to run. */
+        }
+
       bootloader_is_atomic = bootloader != NULL && _ostree_bootloader_is_atomic (bootloader);
 
       /* Note equivalent of try/finally here */
@@ -2375,6 +2390,7 @@ ostree_sysroot_write_deployments_with_options (OstreeSysroot     *self,
     sd_journal_send ("MESSAGE_ID=" SD_ID128_FORMAT_STR, SD_ID128_FORMAT_VAL(OSTREE_DEPLOYMENT_COMPLETE_ID),
                      "MESSAGE=%s", msg,
                      "OSTREE_BOOTLOADER=%s", bootloader ? _ostree_bootloader_get_name (bootloader) : "none",
+                     "OSTREE_BOOTLOADER_CONFIG=%s", bootloader_config,
                      "OSTREE_BOOTLOADER_ATOMIC=%s", bootloader_is_atomic ? "yes" : "no",
                      "OSTREE_DID_BOOTSWAP=%s", requires_new_bootversion ? "yes" : "no",
                      "OSTREE_N_DEPLOYMENTS=%u", new_deployments->len,