init: add an init_mount helper

Like do_mount, but takes a kernel pointer for the destination path.
Switch over the mounts in the init code and devtmpfs to it, which
just happen to work due to the implicit set_fs(KERNEL_DS) during early
init right now.

Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index d697634..32af6cb 100644
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -25,6 +25,7 @@
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/kthread.h>
+#include <linux/init_syscalls.h>
 #include <uapi/linux/mount.h>
 #include "base.h"
 
@@ -359,7 +360,7 @@ int __init devtmpfs_mount(void)
 	if (!thread)
 		return 0;
 
-	err = do_mount("devtmpfs", "dev", "devtmpfs", MS_SILENT, NULL);
+	err = init_mount("devtmpfs", "dev", "devtmpfs", MS_SILENT, NULL);
 	if (err)
 		printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
 	else
@@ -408,7 +409,7 @@ static int __init devtmpfs_setup(void *p)
 	err = ksys_unshare(CLONE_NEWNS);
 	if (err)
 		goto out;
-	err = do_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, NULL);
+	err = init_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, NULL);
 	if (err)
 		goto out;
 	ksys_chdir("/.."); /* will traverse into overmounted root */