From: Neil Horman <nhorman@redhat.com>
Date: Mon, 23 Feb 2009 14:36:38 -0500
Subject: [kexec] add ability to dump log from vmcore file
Message-id: 20090223193638.GC13120@shamino.rdu.redhat.com
O-Subject: [RHEL 5.4 PATCH] kexec: add ability to dump log from vmcore file (bz 485308)
Bugzilla: 485308
RH-Acked-by: Dave Anderson <anderson@redhat.com>

Hey all-
	This is a kernel patch to add needed symbols to implement this
dump_dmesg feature we recently implemented in makedumpfile.  This was in fact
the patch that I was asking about previously regarding the bizzare ABI breakage.
It tunred out I was wrong when I responded to Petes suggestion that there were
some resoved forward declarations that came with the inclusion of kexec.h.  It
turns out you were right pete.  I didn't follow it all the way to the end, but
it became pretty clear that there were some resolved declarations through a
fairly convoluted path through the asm/kexec.h->page.h header files.  Sufficie
it to say, I did something silly in my previous testing, as a subsequent test
showed that doing a __GENKYSYMS__ on kexec.h fixed it right up, as did moving
the include and the new function ot the end of the file.  Brew build here:
https://brewweb.devel.redhat.com/taskinfo?taskID=1696991

This is a backport of the same patch which is sitting in -mm and resolves bz
485308

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 63f688d..fbbdf8f 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -157,6 +157,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 	__attribute__ ((format (printf, 1, 0)));
 asmlinkage int printk(const char * fmt, ...)
 	__attribute__ ((format (printf, 1, 2)));
+extern void log_buf_kexec_setup(void);
 #else
 static inline int vprintk(const char *s, va_list args)
 	__attribute__ ((format (printf, 1, 0)));
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 2e1deb2..24ae9f0 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -197,5 +197,6 @@ struct pt_regs;
 struct task_struct;
 static inline void crash_kexec(struct pt_regs *regs) { }
 static inline int kexec_should_crash(struct task_struct *p) { return 0; }
+#define SYMBOL(x)
 #endif /* CONFIG_KEXEC */
 #endif /* LINUX_KEXEC_H */
diff --git a/kernel/kexec.c b/kernel/kexec.c
index dbb6313..fceb1f0 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -1263,7 +1263,9 @@ static int __init crash_save_vmcoreinfo_init(void)
 	OFFSET(list_head, next);
 	OFFSET(list_head, prev);
 	LENGTH(zone.free_area, MAX_ORDER);
-
+#ifdef CONFIG_PRINTK
+	log_buf_kexec_setup();
+#endif
 	arch_crash_save_vmcoreinfo();
 
 	return 0;
diff --git a/kernel/printk.c b/kernel/printk.c
index d1cb5ea..4f162c0 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -35,6 +35,9 @@
 #include <linux/syscalls.h>
 
 #include <asm/uaccess.h>
+#ifndef __GENKSYMS__
+#include <linux/kexec.h>
+#endif
 
 #define __LOG_BUF_LEN	(1 << CONFIG_LOG_BUF_SHIFT)
 
@@ -125,6 +128,14 @@ static char *log_buf = __log_buf;
 static int log_buf_len = __LOG_BUF_LEN;
 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 
+void log_buf_kexec_setup(void)
+{
+	SYMBOL(log_buf);
+	SYMBOL(log_end);
+	SYMBOL(log_buf_len);
+	SYMBOL(logged_chars);
+}
+
 static int __init log_buf_len_setup(char *str)
 {
 	unsigned long size = memparse(str, &str);