Add rpm-ostree usroverlay

I saw kalev's slides reference `rpm-ostree unlock`; this patch makes it exist.
In general, people have a hard time (understandably) grasping the distinction
between ostree and rpm-ostree; along with the goal of making ostree really
"libostree", let's start wrapping more commands where it makes sense.

I also took this opportunity to have a more descriptive name; it's important
to note that it *doesn't* overlay `/etc`, `/var`, or `/boot` for example.

Closes: #1233
Approved by: jlebon

Makefile-rpm-ostree.am

@@ -32,6 +32,7 @@ rpm_ostree_SOURCES = src/app/main.c \
 	src/app/rpmostree-builtin-cleanup.c \
 	src/app/rpmostree-builtin-initramfs.c \
 	src/app/rpmostree-builtin-livefs.c \
+	src/app/rpmostree-builtin-usroverlay.c \
 	src/app/rpmostree-builtin-override.c \
 	src/app/rpmostree-builtin-refresh-md.c \
 	src/app/rpmostree-pkg-builtins.c \

man/rpm-ostree.xml

@@ -494,6 +494,33 @@ Boston, MA 02111-1307, USA.
         </listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><command>usroverlay</command></term>
+
+        <listitem>
+          <para>
+            Mount a writable overlay filesystem on <literal>/usr</literal> which
+            is active only for the remainder of the system boot. This is
+            intended for development, testing, and debugging. Changes will not
+            persist across upgrades, or rebooting in general.
+          </para>
+
+          <para>
+            One important goal of this is to support traditional <command>rpm
+            -Uvh /path/to/rpms</command> or equivalent where changes are applied
+            live. However, an intended future feature for
+            <command>rpm-ostree</command> will be a variant of
+            <command>rpm-ostree override</command> which also supports applying
+            changes live, for the cases which one wants persistence as well.
+          </para>
+
+          <para>
+            This command is equivalent to <command>ostree admin unlock</command>.
+          </para>
+
+        </listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><command>initramfs</command></term>
 

src/app/main.c

@@ -65,6 +65,13 @@ static RpmOstreeCommand commands[] = {
   { "reload", 0,
     "Reload configuration",
     rpmostree_builtin_reload },
+  { "usroverlay", 0,
+    "Apply a transient overlayfs to /urs",
+    rpmostree_builtin_usroverlay },
+  /* Let's be "cognitively" compatible with `ostree admin unlock` */
+  { "unlock", RPM_OSTREE_BUILTIN_FLAG_HIDDEN,
+    "",
+    rpmostree_builtin_usroverlay },
   { "cancel", 0,
     "Cancel an active transaction",
     rpmostree_builtin_cancel },

src/app/rpmostree-builtin-usroverlay.c

@@ -0,0 +1,61 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
+ *
+ * Copyright (C) 2018 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.
+ */
+
+#include "config.h"
+
+#include <string.h>
+#include <glib-unix.h>
+#include <gio/gio.h>
+
+#include "rpmostree-builtins.h"
+#include "rpmostree-libbuiltin.h"
+
+#include <libglnx.h>
+
+static GOptionEntry option_entries[] = {
+  { NULL }
+};
+
+gboolean
+rpmostree_builtin_usroverlay (int             argc,
+                              char          **argv,
+                              RpmOstreeCommandInvocation *invocation,
+                              GCancellable   *cancellable,
+                              GError        **error)
+{
+  g_autoptr(GOptionContext) context = g_option_context_new ("");
+  glnx_unref_object RPMOSTreeSysroot *sysroot_proxy = NULL;
+  _cleanup_peer_ GPid peer_pid = 0;
+
+  if (!rpmostree_option_context_parse (context,
+                                       option_entries,
+                                       &argc, &argv,
+                                       invocation,
+                                       cancellable,
+                                       NULL, NULL,
+                                       &sysroot_proxy,
+                                       &peer_pid,
+                                       NULL,
+                                       error))
+    return FALSE;
+
+  execlp ("ostree", "ostree", "admin", "unlock", NULL);
+  return glnx_throw_errno_prefix (error, "execvp(ostree admin unlock)");
+}

src/app/rpmostree-builtins.h

@@ -33,6 +33,7 @@ G_BEGIN_DECLS
 BUILTINPROTO(compose);
 BUILTINPROTO(upgrade);
 BUILTINPROTO(reload);
+BUILTINPROTO(usroverlay);
 BUILTINPROTO(deploy);
 BUILTINPROTO(rebase);
 BUILTINPROTO(cancel);

tests/vmcheck/test-basic.sh

@@ -188,3 +188,7 @@ if ! vm_rpmostree install refresh-md-new-pkg --dry-run; then
 fi
 vm_stop_httpd vmcheck
 echo "ok refresh-md"
+
+vm_rpmostree usroverlay
+vm_cmd test -w /usr/bin
+echo "ok usroverlay"