Re: [PATCH v2 3/5] x86: Make set_nmi_callback return the old nmi callback

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 29/05/2014 06:34, Feng Wu wrote:
> 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