[PATCH v3 3/5] x86: Make set_nmi_callback return the old nmi callback

[Feng Wu <feng.wu@intel.com>]

This patch makes set_nmi_callback return the old nmi callback, so
we can set it back later.

Signed-off-by: Feng Wu <feng.wu@intel.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
 xen/arch/x86/traps.c      | 4 +++-
 xen/include/asm-x86/nmi.h | 4 ++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 1722912..171cff0 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -3322,9 +3322,11 @@ void do_nmi(struct cpu_user_regs *regs)
     }
 }
 
-void set_nmi_callback(nmi_callback_t callback)
+nmi_callback_t set_nmi_callback(nmi_callback_t callback)
 {
+    nmi_callback_t old_nmi_callback = nmi_callback;
     nmi_callback = callback;
+    return old_nmi_callback;
 }
 
 void unset_nmi_callback(void)
diff --git a/xen/include/asm-x86/nmi.h b/xen/include/asm-x86/nmi.h
index 98b5e04..58cd9a1 100644
--- a/xen/include/asm-x86/nmi.h
+++ b/xen/include/asm-x86/nmi.h
@@ -15,9 +15,9 @@ typedef int (*nmi_callback_t)(struct cpu_user_regs *regs, int cpu);
  * set_nmi_callback
  *
  * Set a handler for an NMI. Only one handler may be
- * set. Return 1 if the NMI was handled.
+ * set. Return the old nmi callback handler.
  */
-void set_nmi_callback(nmi_callback_t callback);
+nmi_callback_t set_nmi_callback(nmi_callback_t callback);
  
 /** 
  * unset_nmi_callback
-- 
1.8.3.1