[RFC] external module: compatibility with older kernels (SMP and non SMP)

[Carlo Marcelo Arenas Belon <carenas-kLeDWSohozoJb6fo7hG9ng@public.gmane.org>]

The following patch (which is composed of 3 different patches from a series)
has been validated to solve compilation issues observed with kvm-56 in x86
with kernels older than 2.6.21 and are posted here for testing and debate.

The main points accomplished (in the same sequence that the snippets) are :

* kernel <= 2.6.16 doesn't define memcpy or strcmp before used by kvm_para.h
* complement f2601fd2874b94d14dfcb21a3e1b84d7f3262b17 reverting the inclusion
  of io_apic.h which to simplify handling of older kernels
* kernel < 2.6.21 define MAX_IO_APICS to fix non SMP compilations

Remaining issues not yet covered for this patch or the series are :

* kernel < 2.6.19 undefined cpu_online_map in non SMP
* kernel <= 2.6.16 undefined hrtimer-{init,start,cancel}

A fix for the first issue was reverted after regressions were found with non
SMP hosts having SMP guests (which are anyway unreliable even with the last
kernel), the second issue is still open to debate in a separate thread with
the most likely fix (if any) done outside of the external module.

Carlo

--
diff --git a/kernel/external-module-compat.h b/kernel/external-module-compat.h
index 1dc5a96..c6a7d03 100644
--- a/kernel/external-module-compat.h
+++ b/kernel/external-module-compat.h
@@ -9,6 +9,7 @@
 
 #include <linux/compiler.h>
 #include <linux/version.h>
+#include <linux/string.h>
 #include "include/linux/kvm.h"
 #include "include/linux/kvm_para.h"
 #include <linux/cpu.h>
@@ -537,21 +538,6 @@ out:
 #define CONFIG_HAS_IOMEM 1
 #endif
 
-/* Some kernels don't make dest_* available with some configs. */
-
-#include <asm/io_apic.h>
-
-#ifndef dest_Fixed
-#define dest_Fixed        0
-#define dest_LowestPrio   1
-#define dest_SMI          2
-#define dest__reserved_1  3
-#define dest_NMI          4
-#define dest_INIT         5
-#define dest__reserved_2  6
-#define dest_ExtINT       7
-#endif
-
 /* empty_zero_page isn't exported in all kernels */
 #include <asm/pgtable.h>
 
@@ -573,6 +559,11 @@ static inline void blahblah(void)
 
 #endif
 
+/* apicdef.h doesn't get included before 2.6.21 if non-smp */
+#ifndef MAX_IO_APICS
+#define MAX_IO_APICS 64
+#endif
+
 /* X86_FEATURE_NX is missing in some x86_64 kernels */
 
 #include <asm/cpufeature.h>

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