The file init/initramfs.c is always compiled and linked in the kernel
vmlinux even when BLK_DEV_RAM and BLK_DEV_INITRD are disabled and the
system isn't using any form of an initramfs or initrd. In this situation
the code is only used to unpack a (static) default initial rootfilesystem.
The current init/initramfs.c code. usr/initramfs_data.o compiles to a size
of ~15 kbytes. Disabling BLK_DEV_RAM and BLK_DEV_INTRD shrinks the kernel
code size with ~60 Kbytes.
This patch makes it doesn't compile in the code and data for initramfs
support if CONFIG_BLK_DEV_INITRD is not defined. Instead of the initramfs
code and data it uses a small routine in init/noinitramfs.c to setup an
initial static default environment for mounting a rootfilesystem later on
in the kernel initialisation process. The new code is: 164 bytes of size.
The patch is separated in two parts:
1) doesn't compile initramfs code when CONFIG_BLK_DEV_INITRD is not set
2) changing all plaforms vmlinux.lds.S files to not reserve an area of
PAGE_SIZE when CONFIG_BLK_DEV_INITRD is not set.
The patchset is compiled (2.6.10, 2.6.15, 2.6.git) and tested on mips
(PNX8535, kernel version 2.6.10) and arm (IntegratorAP/ARM1176 SoC, kernel
version 2.6.15).
Signed-off-by: Jean-Paul Saman <[email protected]>
----------------------
Index: linux-2.6.git/drivers/block/Kconfig
===================================================================
--- linux-2.6.git.orig/drivers/block/Kconfig 2006-12-14
13:21:54.000000000 +0100
+++ linux-2.6.git/drivers/block/Kconfig 2006-12-14 14:59:38.000000000
+0100
@@ -417,8 +417,10 @@ config BLK_DEV_INITRD
etc. See <file:Documentation/initrd.txt> for details.
If RAM disk support (BLK_DEV_RAM) is also included, this
- also enables initial RAM disk (initrd) support.
+ also enables initial RAM disk (initrd) support and adds
+ 15 Kbytes (more on some other architectures) to the kernel size.
+ If unsure say Y.
config CDROM_PKTCDVD
tristate "Packet writing on CD/DVD media"
Index: linux-2.6.git/init/Makefile
===================================================================
--- linux-2.6.git.orig/init/Makefile 2006-12-14 13:21:54.000000000
+0100
+++ linux-2.6.git/init/Makefile 2006-12-14 14:00:49.000000000 +0100
@@ -2,7 +2,12 @@
# Makefile for the linux kernel.
#
-obj-y := main.o version.o mounts.o initramfs.o
+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-$(CONFIG_GENERIC_CALIBRATE_DELAY) += calibrate.o
mounts-y := do_mounts.o
Index: linux-2.6.git/usr/Makefile
===================================================================
--- linux-2.6.git.orig/usr/Makefile 2006-12-14 13:21:54.000000000
+0100
+++ linux-2.6.git/usr/Makefile 2006-12-14 13:31:29.000000000 +0100
@@ -7,7 +7,7 @@ PHONY += klibcdirs
# Generate builtin.o based on initramfs_data.o
-obj-y := initramfs_data.o
+obj-$(CONFIG_BLK_DEV_INITRD) := initramfs_data.o
# initramfs_data.o contains the initramfs_data.cpio.gz image.
# The image is included using .incbin, a dependency which is not
Index: linux-2.6.git/init/Kconfig
===================================================================
--- linux-2.6.git.orig/init/Kconfig 2006-12-14 13:21:54.000000000
+0100
+++ linux-2.6.git/init/Kconfig 2006-12-14 13:38:44.000000000 +0100
@@ -280,8 +280,12 @@ config RELAY
If unsure, say N.
+if BLK_DEV_INITRD
+
source "usr/Kconfig"
+endif
+
config CC_OPTIMIZE_FOR_SIZE
bool "Optimize for size (Look out for broken compilers!)"
default y
Index: linux-2.6.git/init/noinitramfs.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.git/init/noinitramfs.c 2006-12-14 13:31:29.000000000
+0100
@@ -0,0 +1,43 @@
+/*
+ * init/noinitramfs.c
+ *
+ * Copyright (C) 2006, NXP Semiconductors, All Rights Reserved
+ * Author: Jean-Paul Saman <[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
+ */
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/fcntl.h>
+#include <linux/delay.h>
+#include <linux/string.h>
+#include <linux/syscalls.h>
+
+/*
+ * Create a simple rootfs that is similar to the default initramfs
+ */
+static void __init default_rootfs(void)
+{
+ int mkdir_err = sys_mkdir("/dev", 0755);
+ int err = sys_mknod((const char __user *) "/dev/console",
+ S_IFCHR | S_IRUSR | S_IWUSR,
+ new_encode_dev(MKDEV(5, 1)));
+ if (err == -EROFS )
+ printk( "Warning: Failed to create a rootfs\n" );
+ mkdir_err = sys_mkdir("/root", 0700);
+}
+rootfs_initcall(default_rootfs);
+
---------------------------------
Kind greetings,
Jean-Paul Saman
NXP Semiconductors CTO/RTG DesignIP
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