fs: use nullfs unconditionally as the real rootfs

Remove the "nullfs_rootfs" boot parameter and simply always use nullfs.
The mutable rootfs will be mounted on top of it. Systems that don't use
pivot_root() to pivot away from the real rootfs will have an additional
mount stick around but that shouldn't be a problem at all. If it is
we'll rever this commit.

This also simplifies the boot process and removes the need for the
traditional switch_root workarounds.

Suggested-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 7 insertions, 13 deletions

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 675397c8a7a4..df6847bcf1f2 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -493,21 +493,15 @@ void __init prepare_namespace(void)
 out:
 	devtmpfs_mount();
 
-	if (nullfs_rootfs) {
-		if (init_pivot_root(".", ".")) {
-			pr_err("VFS: Failed to pivot into new rootfs\n");
-			return;
-		}
-		if (init_umount(".", MNT_DETACH)) {
-			pr_err("VFS: Failed to unmount old rootfs\n");
-			return;
-		}
-		pr_info("VFS: Pivoted into new rootfs\n");
+	if (init_pivot_root(".", ".")) {
+		pr_err("VFS: Failed to pivot into new rootfs\n");
 		return;
 	}
-
-	init_mount(".", "/", NULL, MS_MOVE, NULL);
-	init_chroot(".");
+	if (init_umount(".", MNT_DETACH)) {
+		pr_err("VFS: Failed to unmount old rootfs\n");
+		return;
+	}
+	pr_info("VFS: Pivoted into new rootfs\n");
 }
 
 static bool is_tmpfs;