bootloader: Add a zipl bootloader backend

zipl is a bit special in that it parses the BLS config files
directly *but* we need to run the command to update the "boot block".

Hence, we're not generating a separate config file like the other
backends.  Instead, extend the bootloader interface with a `post_bls_sync`
method that is run in the same place we swap the `boot/loader` symlink.

We write a "stamp file" in `/boot` that says we need to run this command.
The reason we use stamp file is to prevent the case where the system is
interrupted after BLS file is updated, but before zipl is triggered,
then zipl boot records are not updated.
This opens the door to making things eventually-consistent/reconcilable
by later adding a systemd unit to run `zipl` if we're interrupted via
a systemd unit - I think we should eventually take this approach
everywhere rather than requiring `/boot/loader` to be a symlink.

Author: Colin Walters <walters@verbum.org>
Tested-by: Tuan Hoang <tmhoang@linux.ibm.com>
Co-Authored-By: Tuan Hoang <tmhoang@linux.ibm.com>

src/libostree/ostree-bootloader-zipl.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2019 Colin Walters <walters@verbum.org>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; either version 2 of the licence or (at
+ * your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General
+ * Public License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#pragma once
+
+#include "ostree-bootloader.h"
+
+G_BEGIN_DECLS
+
+#define OSTREE_TYPE_BOOTLOADER_ZIPL (_ostree_bootloader_zipl_get_type ())
+#define OSTREE_BOOTLOADER_ZIPL(inst) (G_TYPE_CHECK_INSTANCE_CAST ((inst), OSTREE_TYPE_BOOTLOADER_ZIPL, OstreeBootloaderZipl))
+#define OSTREE_IS_BOOTLOADER_ZIPL(inst) (G_TYPE_CHECK_INSTANCE_TYPE ((inst), OSTREE_TYPE_BOOTLOADER_ZIPL))
+
+typedef struct _OstreeBootloaderZipl OstreeBootloaderZipl;
+
+GType _ostree_bootloader_zipl_get_type (void) G_GNUC_CONST;
+
+OstreeBootloaderZipl * _ostree_bootloader_zipl_new (OstreeSysroot *sysroot);
+
+G_END_DECLS