xen/tracing: fix compile errors when tracing is disabled.

When CONFIG_FUNCTION_TRACER is disabled, compilation fails as follows:
  CC      arch/x86/xen/setup.o
In file included from arch/x86/include/asm/xen/hypercall.h:42,
                 from arch/x86/xen/setup.c:19:
include/trace/events/xen.h:31: warning: 'struct multicall_entry' declared inside parameter list
include/trace/events/xen.h:31: warning: its scope is only this definition or declaration, which is probably not what you want
include/trace/events/xen.h:31: warning: 'struct multicall_entry' declared inside parameter list
include/trace/events/xen.h:31: warning: 'struct multicall_entry' declared inside parameter list
include/trace/events/xen.h:31: warning: 'struct multicall_entry' declared inside parameter list
[...]
arch/x86/xen/trace.c:5: error: '__HYPERVISOR_set_trap_table' undeclared here (not in a function)
arch/x86/xen/trace.c:5: error: array index in initializer not of integer type
arch/x86/xen/trace.c:5: error: (near initialization for 'xen_hypercall_names')
arch/x86/xen/trace.c:6: error: '__HYPERVISOR_mmu_update' undeclared here (not in a function)
arch/x86/xen/trace.c:6: error: array index in initializer not of integer type
arch/x86/xen/trace.c:6: error: (near initialization for 'xen_hypercall_names')

Fix this by making sure struct multicall_entry has a declaration in
scope at all times, and don't bother compiling xen/trace.c when tracing
is disabled.

Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/trace/events/xen.h b/include/trace/events/xen.h
index 44d8decee09e..92f1a796829e 100644
--- a/include/trace/events/xen.h
+++ b/include/trace/events/xen.h
@@ -8,6 +8,8 @@
 #include <asm/paravirt_types.h>
 #include <asm/xen/trace_types.h>
 
+struct multicall_entry;
+
 /* Multicalls */
 DECLARE_EVENT_CLASS(xen_mc__batch,
 	    TP_PROTO(enum paravirt_lazy_mode mode),