initramfs: Add skip_initramfs command line option

Add a skip_initramfs option to allow choosing whether to boot using
the initramfs or not at runtime.

Change-Id: If30428fa748c1d4d3d7b9d97c1f781de5e4558c3
Signed-off-by: Rom Lemarchand <[email protected]>

Author: roml

include/linux/initramfs.h

@@ -0,0 +1,32 @@
+/*
+ * include/linux/initramfs.h
+ *
+ * Copyright (C) 2015, Google
+ * Rom Lemarchand <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#ifndef _LINUX_INITRAMFS_H
+#define _LINUX_INITRAMFS_H
+
+#include <linux/kconfig.h>
+
+#if IS_BUILTIN(CONFIG_BLK_DEV_INITRD)
+
+int __init default_rootfs(void);
+
+#endif
+
+#endif /* _LINUX_INITRAMFS_H */

init/Makefile

@@ -3,11 +3,8 @@
 #
 
 obj-y                          := main.o version.o mounts.o
-ifneq ($(CONFIG_BLK_DEV_INITRD),y)
 obj-y                          += noinitramfs.o
-else
 obj-$(CONFIG_BLK_DEV_INITRD)   += initramfs.o
-endif
 obj-$(CONFIG_GENERIC_CALIBRATE_DELAY) += calibrate.o
 
 ifneq ($(CONFIG_ARCH_INIT_TASK),y)

init/initramfs.c

@@ -18,6 +18,7 @@
 #include <linux/dirent.h>
 #include <linux/syscalls.h>
 #include <linux/utime.h>
+#include <linux/initramfs.h>
 
 static __initdata char *message;
 static void __init error(char *x)
@@ -579,9 +580,25 @@ static void __init clean_rootfs(void)
 }
 #endif
 
+static int __initdata do_skip_initramfs;
+
+static int __init skip_initramfs_param(char *str)
+{
+	if (*str)
+		return 0;
+	do_skip_initramfs = 1;
+	return 1;
+}
+__setup("skip_initramfs", skip_initramfs_param);
+
 static int __init populate_rootfs(void)
 {
-	char *err = unpack_to_rootfs(__initramfs_start, __initramfs_size);
+	char *err;
+
+	if (do_skip_initramfs)
+		return default_rootfs();
+
+	err = unpack_to_rootfs(__initramfs_start, __initramfs_size);
 	if (err)
 		panic(err);	/* Failed to decompress INTERNAL initramfs */
 	if (initrd_start) {

init/noinitramfs.c

@@ -21,11 +21,16 @@
 #include <linux/stat.h>
 #include <linux/kdev_t.h>
 #include <linux/syscalls.h>
+#include <linux/kconfig.h>
+#include <linux/initramfs.h>
 
 /*
  * Create a simple rootfs that is similar to the default initramfs
  */
-static int __init default_rootfs(void)
+#if !IS_BUILTIN(CONFIG_BLK_DEV_INITRD)
+static
+#endif
+int __init default_rootfs(void)
 {
 	int err;
 
@@ -49,4 +54,6 @@ static int __init default_rootfs(void)
 	printk(KERN_WARNING "Failed to create a rootfs\n");
 	return err;
 }
+#if !IS_BUILTIN(CONFIG_BLK_DEV_INITRD)
 rootfs_initcall(default_rootfs);
+#endif