container/initoverlay: configure via fsconfig

This works around the page size limit at the cost of negligible performance regressions.

Closes #34.

Signed-off-by: Ophestra <cat@gensokyo.uk>

container/dispatcher.go

@@ -65,6 +65,8 @@ type syscallDispatcher interface {
 	remount(msg message.Msg, target string, flags uintptr) error
 	// mountTmpfs provides mountTmpfs.
 	mountTmpfs(fsname, target string, flags uintptr, size int, perm os.FileMode) error
+	// mountOverlay provides mountOverlay.
+	mountOverlay(target string, options [][2]string) error
 	// ensureFile provides ensureFile.
 	ensureFile(name string, perm, pperm os.FileMode) error
 	// mustLoopback provides mustLoopback.
@@ -169,6 +171,9 @@ func (direct) remount(msg message.Msg, target string, flags uintptr) error {
 func (k direct) mountTmpfs(fsname, target string, flags uintptr, size int, perm os.FileMode) error {
 	return mountTmpfs(k, fsname, target, flags, size, perm)
 }
+func (k direct) mountOverlay(target string, options [][2]string) error {
+	return mountOverlay(target, options)
+}
 func (direct) ensureFile(name string, perm, pperm os.FileMode) error {
 	return ensureFile(name, perm, pperm)
 }