*: console rewrite

This implements {createTTY, detach} and all of the combinations and
negations of the two that were previously implemented. There are some
valid questions about out-of-OCI-scope topics like !createTTY and how
things should be handled (why do we dup the current stdio to the
process, and how is that not a security issue). However, these will be
dealt with in a separate patchset.

In order to allow for late console setup, split setupRootfs into the
"preparation" section where all of the mounts are created and the
"finalize" section where we pivot_root and set things as ro. In between
the two we can set up all of the console mountpoints and symlinks we
need.

We use two-stage synchronisation to ensures that when the syscalls are
reordered in a suboptimal way, an out-of-place read() on the parentPipe
will not gobble the ancilliary information.

This patch is part of the console rewrite patchset.

Signed-off-by: Aleksa Sarai <asarai@suse.de>

restore.go

@@ -158,15 +158,16 @@ func restoreContainer(context *cli.Context, spec *specs.Spec, config *configs.Co
 		defer destroy(container)
 	}
 	process := &libcontainer.Process{}
-	tty, err := setupIO(process, rootuid, rootgid, "", false, detach)
+	tty, err := setupIO(process, rootuid, rootgid, false, detach)
 	if err != nil {
 		return -1, err
 	}
-	defer tty.Close()
-	handler := newSignalHandler(tty, !context.Bool("no-subreaper"))
+	handler := newSignalHandler(!context.Bool("no-subreaper"))
 	if err := container.Restore(process, options); err != nil {
 		return -1, err
 	}
+	// We don't need to do a tty.recvtty because config.Terminal is always false.
+	defer tty.Close()
 	if err := tty.ClosePostStart(); err != nil {
 		return -1, err
 	}
@@ -180,7 +181,7 @@ func restoreContainer(context *cli.Context, spec *specs.Spec, config *configs.Co
 	if detach {
 		return 0, nil
 	}
-	return handler.forward(process)
+	return handler.forward(process, tty)
 }
 
 func criuOptions(context *cli.Context) *libcontainer.CriuOpts {