Re: Reducing root filesystem

[Jan-Benedict Glaw <jbglaw@lug-owl.de>]

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On Wed, 2002-04-10 19:38:09 +0530, Amol Kumar Lad <amolk@ishoni.com>
wrote in message <7CFD7CA8510CD6118F950002A519EA3001067D06@leonoid.in.ishoni.com>:
> Hi,
>   I am porting Linux to an embedded system. Currently my rootfilesystem is
> around 2.5 MB (after keeping it to minimal and adding tools like busybox). I
> want to furthur reduce it to say maximum of 1.5 MB. 
> Please suggest some link/references where I can find the details to optimise
> my root filesystem

I really can't help you with the root filesystem, but you can do sth
like this:


diff -Nur test-remove-me/linux-2.2.19-clean/Documentation/Configure.help linux-schlecker-2.2.19/Documentation/Configure.help
--- test-remove-me/linux-2.2.19-clean/Documentation/Configure.help	Sun Mar 25 18:37:29 2001
+++ linux-schlecker-2.2.19/Documentation/Configure.help	Mon Nov  5 12:42:46 2001
@@ -4942,6 +4942,14 @@
   important data. This is primarily of use to people trying to debug
   the middle and upper layers of the SCSI subsystem. If unsure, say N.
 
+Smaller kernel by omitting most messages
+CONFIG_NO_PRINTK
+  Enabling this option will result in a smaller kernel by removing
+  most text strings. This is only useful for emdedded systems where
+  you've got to live with <= 4MB of RAM. I386-only for now...
+
+  If unsure, say no.
+
 Fibre Channel support
 CONFIG_FC4
   This is an experimental support for storage arrays connected to
@@ -210,5 +221,6 @@
 
 #bool 'Debug kmalloc/kfree' CONFIG_DEBUG_MALLOC
 bool 'Magic SysRq key' CONFIG_MAGIC_SYSRQ
+bool 'Eleminate *most* printk()s' CONFIG_NO_PRINTK
 endmenu
 
diff -Nur test-remove-me/linux-2.2.19-clean/arch/i386/kernel/head.S linux-schlecker-2.2.19/arch/i386/kernel/head.S
--- test-remove-me/linux-2.2.19-clean/arch/i386/kernel/head.S	Sun Mar 25 18:31:45 2001
+++ linux-schlecker-2.2.19/arch/i386/kernel/head.S	Fri Nov  2 11:21:42 2001
@@ -315,7 +315,7 @@
 	movl %ax,%ds
 	movl %ax,%es
 	pushl $int_msg
-	call SYMBOL_NAME(printk)
+	call SYMBOL_NAME(real_printk)
 	popl %eax
 	popl %ds
 	popl %es
diff -Nur test-remove-me/linux-2.2.19-clean/include/asm-i386/system.h linux-schlecker-2.2.19/include/asm-i386/system.h
--- test-remove-me/linux-2.2.19-clean/include/asm-i386/system.h	Sun Mar 25 18:31:05 2001
+++ linux-schlecker-2.2.19/include/asm-i386/system.h	Mon Dec 17 14:32:03 2001
@@ -135,21 +135,15 @@
 	switch (size) {
 		case 1:
 			__asm__("xchgb %b0,%1"
-				:"=q" (x)
-				:"m" (*__xg(ptr)), "0" (x)
-				:"memory");
+					:"+q" (x),"=m" (*__xg(ptr)));
 			break;
 		case 2:
 			__asm__("xchgw %w0,%1"
-				:"=r" (x)
-				:"m" (*__xg(ptr)), "0" (x)
-				:"memory");
+					:"+r" (x),"=m" (*__xg(ptr)));
 			break;
 		case 4:
 			__asm__("xchgl %0,%1"
-				:"=r" (x)
-				:"m" (*__xg(ptr)), "0" (x)
-				:"memory");
+					:"+r" (x), "=m" (*__xg(ptr)));
 			break;
 	}
 	return x;
diff -Nur test-remove-me/linux-2.2.19-clean/include/linux/kernel.h linux-schlecker-2.2.19/include/linux/kernel.h
--- test-remove-me/linux-2.2.19-clean/include/linux/kernel.h	Sun Mar 25 18:31:03 2001
+++ linux-schlecker-2.2.19/include/linux/kernel.h	Fri Dec 14 14:53:14 2001
@@ -9,6 +9,7 @@
 
 #include <stdarg.h>
 #include <linux/linkage.h>
+#include <linux/config.h>
 
 /* Optimization barrier */
 /* The "volatile" is due to gcc bugs */
@@ -54,8 +55,16 @@
 
 extern int session_of_pgrp(int pgrp);
 
-asmlinkage int printk(const char * fmt, ...)
+asmlinkage int real_printk(const char * fmt, ...)
 	__attribute__ ((format (printf, 1, 2)));
+
+#ifdef CONFIG_NO_PRINTK
+#	define printk(format, arg...) do {} while(0)
+#else
+#	define printk(format, arg...) real_printk(format, ## arg)
+#endif /* CONFIG_NO_PRINTK */
+
+#define oops_printk(format, arg...) real_printk(format, ## arg)
 
 #if DEBUG
 #define pr_debug(fmt,arg...) \
diff -Nur test-remove-me/linux-2.2.19-clean/kernel/ksyms.c linux-schlecker-2.2.19/kernel/ksyms.c
--- test-remove-me/linux-2.2.19-clean/kernel/ksyms.c	Sun Mar 25 18:31:02 2001
+++ linux-schlecker-2.2.19/kernel/ksyms.c	Fri Dec 14 15:24:52 2001
@@ -357,7 +357,7 @@
 
 /* misc */
 EXPORT_SYMBOL(panic);
-EXPORT_SYMBOL(printk);
+EXPORT_SYMBOL(real_printk);
 EXPORT_SYMBOL(sprintf);
 EXPORT_SYMBOL(vsprintf);
 EXPORT_SYMBOL(kdevname);
diff -Nur test-remove-me/linux-2.2.19-clean/kernel/printk.c linux-schlecker-2.2.19/kernel/printk.c
--- test-remove-me/linux-2.2.19-clean/kernel/printk.c	Sun Mar 25 18:31:02 2001
+++ linux-schlecker-2.2.19/kernel/printk.c	Fri Dec 14 14:52:50 2001
@@ -249,7 +249,7 @@
 	return do_syslog(type, buf, len);
 }
 
-asmlinkage int printk(const char *fmt, ...)
+asmlinkage int real_printk(const char *fmt, ...)
 {
 	va_list args;
 	int i;




This is for i386, but it can be implemented like this for other
architectures. Please note:

	- The patch to system.h is only neccessary because gcc will
	  magically miscompile the code if there's no printk()
	  resulting (at least) in a broken DMA (de)registering
	  functions rendering the floppy.o module useless. Maybe
	  you don't need this patch. It was _not_ developed by
	  me but send by Momchil Velikov <velco@fadata.bg>.
	- In 2.4.x, EXPORT_SYMBOL((real)printk) is not in
	  kernel/ksyms.c, but in kernel/printk.c
	- BigFatWarning: It shouldn't be, but there might
	  be code fragments that do more than only printing
	  in a printk call (like 'printk(KERN_ERR "%d\n", a=func(a))')
	  Things like this _will_ break!!!

MfG, JBG

-- 
Jan-Benedict Glaw   .   jbglaw@lug-owl.de   .   +49-172-7608481
	 -- New APT-Proxy written in shell script --
	   http://lug-owl.de/~jbglaw/software/ap2/

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