[PATCH 3/5] Wire up CONFIG_DEVTMPFS_MOUNT to initramfs.

[Rob Landley]

The kernel has had CONFIG_DEVTMPFS_MOUNT for years, but it only applied to
fallback ROOT= not initramfs/initmpfs. As long as the config option exists,
it might as well work.

I use this for board bringup: populating a chdir and calling cpio as a
normal user often leaves /dev empty (because mknod requires root access),
meaning no /dev/console for init/main.c to open, meaning init runs without
stdin/stdout/stderr and has to mount devtmpfs and redirect the filehandles
blind with no error output if something goes wrong.

Signed-off-by: Rob Landley <rob@xxxxxxxxxxx>
Previously: https://lkml.org/lkml/2017/9/13/651
---
 init/main.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/init/main.c b/init/main.c
index e1c3911d7c70..eca7ba2c2764 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1636,7 +1636,6 @@ static noinline void __init kernel_init_freeable(void)
 	kunit_run_all_tests();
 
 	wait_for_initramfs();
-	console_on_rootfs();
 
 	/*
 	 * check if there is an early userspace init.  If yes, let it do all
@@ -1645,7 +1644,11 @@ static noinline void __init kernel_init_freeable(void)
 	if (init_eaccess(ramdisk_execute_command) != 0) {
 		ramdisk_execute_command = NULL;
 		prepare_namespace();
+	} else if (IS_ENABLED(CONFIG_DEVTMPFS_MOUNT)) {
+		init_mkdir("/dev", 0755);
+		devtmpfs_mount();
 	}
+	console_on_rootfs();
 
 	/*
 	 * Ok, we have completed the initial bootup, and