Re: [patch] SMP alternatives: skip with UP kernels.

[Gerd Hoffmann <kraxel@suse.de>]

>> Patch below.  It simply returns in case the tables are empty and nothing
>> is do to, thus avoids printing the confusing message.
> 
> It does avoid the message but well, that's also _all_ it avoids. Why do
> you want to do it this way?  [ ... patch ... ]
> 
> Yes, the #ifdef in arch/i386/kernel/module.c is a bit clumsy.

Yep, thats why.  I wanted avoid exactly that.  Having some code need to
know that function foobar() is only available with CONFIG_BAZ is set is
really ugly ...

The attached patch hides the magic in alternative.h and provides some
dummy inline functions for the UP case (gcc should manage to optimize
away these calls).  No changes in module.c.

cheers,

  Gerd

-- 
Gerd Hoffmann <kraxel@suse.de>
Erst mal heiraten, ein, zwei Kinder, und wenn alles läuft
geh' ich nach drei Jahren mit der Familie an die Börse.
http://www.suse.de/~kraxel/julika-dora.jpeg

Index: vanilla-2.6.17-rc3-mm1/arch/i386/kernel/alternative.c
===================================================================
--- vanilla-2.6.17-rc3-mm1.orig/arch/i386/kernel/alternative.c	2006-05-10 12:25:39.000000000 +0200
+++ vanilla-2.6.17-rc3-mm1/arch/i386/kernel/alternative.c	2006-05-12 10:03:40.000000000 +0200
@@ -168,6 +168,8 @@ void apply_alternatives(struct alt_instr
 	}
 }
 
+#ifdef CONFIG_SMP
+
 static void alternatives_smp_save(struct alt_instr *start, struct alt_instr *end)
 {
 	struct alt_instr *a;
@@ -328,6 +330,8 @@ void alternatives_smp_switch(int smp)
 	spin_unlock_irqrestore(&smp_alt, flags);
 }
 
+#endif
+
 void __init alternative_instructions(void)
 {
 	if (no_replacement) {
@@ -349,6 +353,7 @@ void __init alternative_instructions(voi
 	smp_alt_once = 1;
 #endif
 
+#ifdef CONFIG_SMP
 	if (smp_alt_once) {
 		if (1 == num_possible_cpus()) {
 			printk(KERN_INFO "SMP alternatives: switching to UP code\n");
@@ -370,4 +375,5 @@ void __init alternative_instructions(voi
 					    _text, _etext);
 		alternatives_smp_switch(0);
 	}
+#endif
 }
Index: vanilla-2.6.17-rc3-mm1/include/asm-i386/alternative.h
===================================================================
--- vanilla-2.6.17-rc3-mm1.orig/include/asm-i386/alternative.h	2006-05-09 18:56:14.000000000 +0200
+++ vanilla-2.6.17-rc3-mm1/include/asm-i386/alternative.h	2006-05-12 10:06:28.000000000 +0200
@@ -17,11 +17,19 @@ struct alt_instr {
 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
 
 struct module;
+#ifdef CONFIG_SMP
 extern void alternatives_smp_module_add(struct module *mod, char *name,
 					void *locks, void *locks_end,
 					void *text, void *text_end);
 extern void alternatives_smp_module_del(struct module *mod);
 extern void alternatives_smp_switch(int smp);
+#else
+static inline void alternatives_smp_module_add(struct module *mod, char *name,
+					void *locks, void *locks_end,
+					void *text, void *text_end) {}
+static inline void alternatives_smp_module_del(struct module *mod) {}
+static inline void alternatives_smp_switch(int smp) {}
+#endif
 
 #endif
 
Index: vanilla-2.6.17-rc3-mm1/include/asm-x86_64/alternative.h
===================================================================
--- vanilla-2.6.17-rc3-mm1.orig/include/asm-x86_64/alternative.h	2006-05-09 18:56:14.000000000 +0200
+++ vanilla-2.6.17-rc3-mm1/include/asm-x86_64/alternative.h	2006-05-12 10:05:26.000000000 +0200
@@ -17,11 +17,20 @@ struct alt_instr {
 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
 
 struct module;
+
+#ifdef CONFIG_SMP
 extern void alternatives_smp_module_add(struct module *mod, char *name,
 					void *locks, void *locks_end,
 					void *text, void *text_end);
 extern void alternatives_smp_module_del(struct module *mod);
 extern void alternatives_smp_switch(int smp);
+#else
+static inline void alternatives_smp_module_add(struct module *mod, char *name,
+					void *locks, void *locks_end,
+					void *text, void *text_end) {}
+static inline void alternatives_smp_module_del(struct module *mod) {}
+static inline void alternatives_smp_switch(int smp) {}
+#endif
 
 #endif