bwrap: Split out a "base" constructor

The bwrap code has some "opinionated" setup around e.g. /etc and
such that I'd like to centralize even more.  However, the dracut
case of taking the host's `/etc` is the unusual standout.  Let's
split out a base constructor.

Prep for https://github.com/projectatomic/rpm-ostree/issues/1329

Closes: #1333
Approved by: jlebon

src/libpriv/rpmostree-bwrap.c

@@ -201,12 +201,8 @@ running_in_nspawn (void)
 }
 
 RpmOstreeBwrap *
-rpmostree_bwrap_new (int rootfs_fd,
-                     RpmOstreeBwrapMutability mutable,
-                     GError **error,
-                     ...)
+rpmostree_bwrap_new_base (int rootfs_fd, GError **error)
 {
-  va_list args;
   g_autoptr(RpmOstreeBwrap) ret = g_new0 (RpmOstreeBwrap, 1);
   static const char *usr_links[] = {"lib", "lib32", "lib64", "bin", "sbin"};
 
@@ -301,6 +297,20 @@ rpmostree_bwrap_new (int rootfs_fd,
       rpmostree_bwrap_append_bwrap_argv (ret, "--symlink", srcpath, destpath, NULL);
     }
 
+  return g_steal_pointer (&ret);
+}
+
+RpmOstreeBwrap *
+rpmostree_bwrap_new (int rootfs_fd,
+                     RpmOstreeBwrapMutability mutable,
+                     GError **error,
+                     ...)
+{
+  g_autoptr(RpmOstreeBwrap) ret = rpmostree_bwrap_new_base (rootfs_fd, error);
+  if (!ret)
+    return FALSE;
+
+  va_list args;
   switch (mutable)
     {
     case RPMOSTREE_BWRAP_IMMUTABLE:
@@ -315,12 +325,11 @@ rpmostree_bwrap_new (int rootfs_fd,
       break;
     }
 
-  { const char *arg;
-    va_start (args, error);
-    while ((arg = va_arg (args, char *)))
-      g_ptr_array_add (ret->argv, g_strdup (arg));
-    va_end (args);
-  }
+  const char *arg;
+  va_start (args, error);
+  while ((arg = va_arg (args, char *)))
+    g_ptr_array_add (ret->argv, g_strdup (arg));
+  va_end (args);
 
   return g_steal_pointer (&ret);
 }

src/libpriv/rpmostree-bwrap.h

@@ -38,6 +38,8 @@ G_DEFINE_AUTOPTR_CLEANUP_FUNC(RpmOstreeBwrap, rpmostree_bwrap_unref)
 /* TODO - move this utility elsewhere */
 void rpmostree_ptrarray_append_strdup (GPtrArray *argv_array, ...) G_GNUC_NULL_TERMINATED;
 
+RpmOstreeBwrap *rpmostree_bwrap_new_base (int rootfs, GError **error);
+
 RpmOstreeBwrap *rpmostree_bwrap_new (int rootfs,
                                      RpmOstreeBwrapMutability mutable,
                                      GError **error,

src/libpriv/rpmostree-kernel.c

@@ -437,15 +437,25 @@ rpmostree_run_dracut (int     rootfs_dfd,
    * config files.  Otherwise, we use the usr/etc defaults.
    */
   if (rebuild_from_initramfs)
-    bwrap = rpmostree_bwrap_new (rootfs_dfd, RPMOSTREE_BWRAP_IMMUTABLE, error,
-                                 "--ro-bind", "/etc", "/etc",
-                                 NULL);
+    {
+      bwrap = rpmostree_bwrap_new_base (rootfs_dfd, error);
+      if (!bwrap)
+        return FALSE;
+      rpmostree_bwrap_append_bwrap_argv (bwrap,
+                                         "--ro-bind", "/etc", "/etc",
+                                         "--ro-bind", "usr", "/usr",
+                                         NULL);
+    }
   else
-    bwrap = rpmostree_bwrap_new (rootfs_dfd, RPMOSTREE_BWRAP_IMMUTABLE, error,
-                                 "--ro-bind", "usr/etc", "/etc",
-                                 NULL);
-  if (!bwrap)
-    return FALSE;
+    {
+      bwrap = rpmostree_bwrap_new_base (rootfs_dfd, error);
+      if (!bwrap)
+        return FALSE;
+      rpmostree_bwrap_append_bwrap_argv (bwrap,
+                                        "--ro-bind", "usr/etc", "/etc",
+                                        "--ro-bind", "usr", "/usr",
+                                        NULL);
+    }
 
   if (dracut_host_tmpdir)
     rpmostree_bwrap_append_bwrap_argv (bwrap, "--bind", dracut_host_tmpdir->path, "/tmp/dracut", NULL);