[PATCH] tools: libxc: do not redefine evtchn_port_or_error_t in xc_evtchn_compat.c

[Ian Campbell <ian.campbell@citrix.com>]

This file stradles the xenevtchn and libxc evtchn_compat worlds, and
hence ends up with two evtchn_port_or_error_t typedefs which older
gcc's (and the C standard) do not like.

Avoid this by gating the compat definition on a gate provided by the
compat implementation.

Note that this would still be broken by an application which does:
    #define XC_WANT_COMPAT_EVTCHN_API
    #include <xenevtchn.h>
    #include <xenctrl.h>

Which effectively means that an application must be ported over to
xenevtchn in one go rather than incrementally (e.g. if it uses
evtchn's for multiple purposes). Since the port is actually fairly
mechanical I hope this is acceptable.

Reported-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
---
I'm not super happy about this approach, due to the caveat in the
second half of the commit message.

Other approaches:

rename the libxenevtchn type, e.g.  xenevtchn_port_or_error_t?

Some sort of skank based on the header guard #defines, but that's
awful (and fragile).
---
 tools/libxc/include/xenctrl_compat.h | 2 ++
 tools/libxc/xc_evtchn_compat.c       | 1 +
 2 files changed, 3 insertions(+)

diff --git a/tools/libxc/include/xenctrl_compat.h b/tools/libxc/include/xenctrl_compat.h
index 93ccadb..afc3d88 100644
--- a/tools/libxc/include/xenctrl_compat.h
+++ b/tools/libxc/include/xenctrl_compat.h
@@ -51,7 +51,9 @@ void *xc_map_foreign_bulk(xc_interface *xch, uint32_t dom, int prot,
 #ifdef XC_WANT_COMPAT_EVTCHN_API
 
 typedef struct xenevtchn_handle xc_evtchn;
+#ifndef XC_BUILDING_COMPAT_EVTCHN_API
 typedef xc_evtchn_port_or_error_t evtchn_port_or_error_t;
+#endif
 
 xc_evtchn *xc_evtchn_open(xentoollog_logger *logger,
                              unsigned open_flags);
diff --git a/tools/libxc/xc_evtchn_compat.c b/tools/libxc/xc_evtchn_compat.c
index 5d3e4ba..99da476 100644
--- a/tools/libxc/xc_evtchn_compat.c
+++ b/tools/libxc/xc_evtchn_compat.c
@@ -6,6 +6,7 @@
 #include <xenevtchn.h>
 
 #define XC_WANT_COMPAT_EVTCHN_API
+#define XC_BUILDING_COMPAT_EVTCHN_API
 #include "xenctrl.h"
 
 xc_evtchn *xc_evtchn_open(xentoollog_logger *logger,
-- 
2.1.4