/proc/config reducing kernel image size

From: Tom Fredrik Blenning Klaussen
Date: Tue Sep 14 2004 - 12:14:45 EST

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I've written a small patch that reduces the size of /proc/config.

There is no point in storing all the comments and unused options in the
kernel image. This typically reduces the config size to about 1/5th
before compressing, and to about 1/4th after compressing.

I've also added the configuration option of how you want to compress it.

In order to do the comment stripping I was forced to add a small script
to the scripts, section, this has to be made executable. However if it
is possible, the script should be skipped altogether, but I can't figure
out how to do the proper escaping of the special characters in the
kernel/Makefile. So if anyone could help me with that, I would be
grateful.

I'm interessted in comments on the concept.

Sincerely
--
BFG
diff -ruN /usr/src/linux-2.6.8.1/init/Kconfig ./init/Kconfig
--- /usr/src/linux-2.6.8.1/init/Kconfig 2004-08-31 13:11:45.000000000 +0200
+++ ./init/Kconfig 2004-09-12 19:51:06.000000000 +0200
@@ -197,6 +197,8 @@
agent" (/sbin/hotplug) to load modules and set up software needed
to use devices as you hotplug them.

+menu "Kernel .config support"
+
config IKCONFIG
bool "Kernel .config support"
---help---
@@ -209,13 +211,71 @@
It can also be extracted from a running kernel by reading
/proc/config.gz if enabled (below).

-config IKCONFIG_PROC
- bool "Enable access to .config through /proc/config.gz"
- depends on IKCONFIG && PROC_FS
+config IKCONFIG_STRIP
+ bool "Strip comments and unused options"
+ depends on IKCONFIG
+ ---help---
+ This option strips all comments and options that increases
+ human readability, but are unnecessary for the parsing
+ process.
+
+choice
+ prompt "Config compression method"
+ depends on IKCONFIG
+ default IKCONFIG_COMPRESS_NONE
+ ---help---
+ Choose which kind of compression that will be used for the
+ kernel copy of the config file.
+
+config IKCONFIG_COMPRESS_NONE
+ bool "None"
+ ---help---
+ This option disables config file compression.
+
+
+config IKCONFIG_COMPRESS_GZIP
+ bool "Gzip"
+ ---help---
+ This option enables gzip config file compression.
+
+ Gzip is the standard compression utility that can be found on
+ any UNIX machine.
+
+config IKCONFIG_COMPRESS_BZIP2
+ bool "Bzip2 (RECOMMENDED)"
---help---
- This option enables access to the kernel configuration file
- through /proc/config.gz.
+ This option enables bzip2 config file compression.
+
+ Bzip2 is designed for text compression, and is slightly better
+ than gzip for this purpose.

+endchoice
+
+config IKCONFIG_PROC
+ bool "Enable access to .config through /proc/config"
+ depends on IKCONFIG_COMPRESS_NONE && PROC_FS
+ ---help---
+ This option enables access to the kernel configuration file
+ through /proc/config.
+
+
+config IKCONFIG_PROC
+ bool "Enable access to .config through /proc/config.gz"
+ depends on IKCONFIG_COMPRESS_GZIP && PROC_FS
+ ---help---
+ This option enables access to the kernel configuration file
+ through /proc/config.gz.
+
+
+config IKCONFIG_PROC
+ bool "Enable access to .config through /proc/config.bz2"
+ depends on IKCONFIG_COMPRESS_BZIP2 && PROC_FS
+ ---help---
+ This option enables access to the kernel configuration file
+ through /proc/config.bz2.
+
+
+endmenu

menuconfig EMBEDDED
bool "Configure standard kernel features (for small systems)"
diff -ruN /usr/src/linux-2.6.8.1/kernel/Makefile ./kernel/Makefile
--- /usr/src/linux-2.6.8.1/kernel/Makefile 2004-08-31 13:11:45.000000000 +0200
+++ ./kernel/Makefile 2004-09-12 20:08:02.000000000 +0200
@@ -19,6 +19,8 @@
obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
obj-$(CONFIG_COMPAT) += compat.o
obj-$(CONFIG_IKCONFIG) += configs.o
+#Is this strictly needed? CONFIG_IKCONFIG_PROC should only be defined
+# if CONFIG_IKCONFIG is defined.
obj-$(CONFIG_IKCONFIG_PROC) += configs.o
obj-$(CONFIG_STOP_MACHINE) += stop_machine.o
obj-$(CONFIG_AUDIT) += audit.o
@@ -35,14 +37,48 @@

$(obj)/configs.o: $(obj)/config_data.h

-# config_data.h contains the same information as ikconfig.h but gzipped.
-# Info from config_data can be extracted from /proc/config*
-targets += config_data.gz
-$(obj)/config_data.gz: .config FORCE
- $(call if_changed,gzip)

-quiet_cmd_ikconfiggz = IKCFG $@
- cmd_ikconfiggz = (echo "const char kernel_config_data[] = MAGIC_START"; cat $< | scripts/bin2c; echo "MAGIC_END;") > $@
+#define the stripping command, basically strip or copy
+ifdef CONFIG_IKCONFIG_STRIP
+quiet_cmd_ikconfig_strip = STRIP $@
+ cmd_ikconfig_strip = scripts/stripCommBlank.sh < $< > $@
+else
+quiet_cmd_ikconfig_strip = COPY $@
+ cmd_ikconfig_strip = cp $< $@
+endif
+
+# config_data_in contains the (stripped?) config file
+targets += config_data_in
+$(obj)/config_data_in: .config FORCE
+ $(call if_changed,ikconfig_strip)
+
+
+#define the compression command, none,gzip or bzip2
+ifdef CONFIG_IKCONFIG_COMPRESS_NONE
+quiet_cmd_ikconfig_compress = COPY $@
+ cmd_ikconfig_compress = cp $< $@
+endif
+
+ifdef CONFIG_IKCONFIG_COMPRESS_GZIP
+quiet_cmd_ikconfig_compress = GZIP $@
+ cmd_ikconfig_compress = gzip --best < $< > $@
+endif
+
+ifdef CONFIG_IKCONFIG_COMPRESS_BZIP2
+quiet_cmd_ikconfig_compress = BZIP2 $@
+ cmd_ikconfig_compress = bzip2 --best < $< > $@
+endif
+
+
+# config_data_compressed contains the (compressed?) config file
+targets += config_data_compressed
+$(obj)/config_data_compressed: $(obj)/config_data_in FORCE
+ $(call if_changed,ikconfig_compress)
+
+quiet_cmd_ikconfig = IKCFG $@
+ cmd_ikconfig = (echo "const char kernel_config_data[] = MAGIC_START"; cat $< | scripts/bin2c; echo "MAGIC_END;") > $@
+
+# Info from config_data can be extracted from /proc/config*
targets += config_data.h
-$(obj)/config_data.h: $(obj)/config_data.gz FORCE
- $(call if_changed,ikconfiggz)
+$(obj)/config_data.h: $(obj)/config_data_compressed FORCE
+ $(call if_changed,ikconfig)
diff -ruN /usr/src/linux-2.6.8.1/kernel/configs.c ./kernel/configs.c
--- /usr/src/linux-2.6.8.1/kernel/configs.c 2004-08-31 13:11:45.000000000 +0200
+++ ./kernel/configs.c 2004-09-12 19:51:06.000000000 +0200
@@ -55,6 +55,16 @@

#ifdef CONFIG_IKCONFIG_PROC

+#ifdef CONFIG_IKCONFIG_COMPRESS_NONE
+#define PROC_CONFIG_FILENAME "config"
+#elif CONFIG_IKCONFIG_COMPRESS_GZIP
+#define PROC_CONFIG_FILENAME "config.gz"
+#elif CONFIG_IKCONFIG_COMPRESS_BZIP2
+#define PROC_CONFIG_FILENAME "config.bz2"
+#else
+#error Proc config filename could not be defined
+#endif
+
/**************************************************/
/* globals and useful constants */

@@ -89,7 +99,7 @@
struct proc_dir_entry *entry;

/* create the current config file */
- entry = create_proc_entry("config.gz", S_IFREG | S_IRUGO,
+ entry = create_proc_entry(PROC_CONFIG_FILENAME, S_IFREG | S_IRUGO,
&proc_root);
if (!entry)
return -ENOMEM;
diff -ruN /usr/src/linux-2.6.8.1/scripts/stripCommBlank.sh ./scripts/stripCommBlank.sh
--- /usr/src/linux-2.6.8.1/scripts/stripCommBlank.sh 1970-01-01 01:00:00.000000000 +0100
+++ ./scripts/stripCommBlank.sh 2004-09-12 19:51:06.000000000 +0200
@@ -0,0 +1,2 @@
+#!/bin/sh
+egrep -v '^#|^[:space:]*$'

Next message: Andreas Dilger: "Re: Kernel stack overflow on 2.6.9-rc2"
Previous message: Alan Cox: "PATCH: tty locking for 2.6.9rc2"
Next in thread: DervishD: "Re: /proc/config reducing kernel image size"
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