GCC reports:

In file included from hvm.c:24:0:
/local/xen.git/xen/include/xen/trace.h: In function ‘tb_control’:
/local/xen.git/xen/include/xen/trace.h:60:13: error: ‘ENOSYS’
undeclared (first use in this function)
     return -ENOSYS;
             ^~~~~~

Include xen/errno.h to resolve the issue.  While tweaking this, add comments
to the #else and #endif, as they are a fair distance apart.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: George Dunlap <George.Dunlap@eu.citrix.com>
CC: Ian Jackson <ian.jackson@citrix.com>
CC: Jan Beulich <JBeulich@suse.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Tim Deegan <tim@xen.org>
CC: Wei Liu <wl@xen.org>
CC: Julien Grall <julien.grall@arm.com>
---
 xen/include/xen/trace.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/xen/include/xen/trace.h b/xen/include/xen/trace.h
index fad92c784a..e6a4ef93cc 100644
--- a/xen/include/xen/trace.h
+++ b/xen/include/xen/trace.h
@@ -53,7 +53,10 @@ static inline void trace_var(u32 event, int cycles, int extra,
 void __trace_hypercall(uint32_t event, unsigned long op,
                        const xen_ulong_t *args);
 
-#else
+#else /* CONFIG_TRACEBUFFER */
+
+#include <xen/errno.h>
+
 static inline void init_trace_bufs(void) {}
 static inline int tb_control(struct xen_sysctl_tbuf_op *tbc)
 {
@@ -71,7 +74,7 @@ static inline void __trace_var(uint32_t event, bool cycles, unsigned int extra,
                                const void *extra_data) {}
 static inline void __trace_hypercall(uint32_t event, unsigned long op,
                                      const xen_ulong_t *args) {}
-#endif
+#endif /* CONFIG_TRACEBUFFER */
 
 /* Convenience macros for calling the trace function. */
 #define TRACE_0D(_e)                            \
-- 
2.11.0


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On 18.07.2019 16:00, Andrew Cooper wrote:
> GCC reports:
> 
> In file included from hvm.c:24:0:
> /local/xen.git/xen/include/xen/trace.h: In function ‘tb_control’:
> /local/xen.git/xen/include/xen/trace.h:60:13: error: ‘ENOSYS’
> undeclared (first use in this function)
>       return -ENOSYS;
>               ^~~~~~
> 
> Include xen/errno.h to resolve the issue.  While tweaking this, add comments
> to the #else and #endif, as they are a fair distance apart.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Acked-by: Jan Beulich <jbeulich@suse.com>

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