[PATCH v4] xen/errno: Reduce complexity of inclusion

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

The inclusion rules conditions for errno.h were unnecesserily complicated, and
required the includer to jump through hoops if they wished to avoid getting
multiple namespaces worth of constants.

Simply the logic, and document what is going on.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Tim Deegan <tim@xen.org>
CC: Doug Goldstein <cardoe@cardoe.com>

v3:
 * Reinstate magic documentation comments
 * Provide assembly-suitable defaults if appropriate

v4:
 * Reintroduce broken #undef logic to be bug-compatible with the previous
   version.
---
 xen/include/public/errno.h | 41 ++++++++++++++++++++++++++++++++++-------
 xen/include/xen/errno.h    |  6 ++----
 2 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/xen/include/public/errno.h b/xen/include/public/errno.h
index dbac396..a0dd0cf 100644
--- a/xen/include/public/errno.h
+++ b/xen/include/public/errno.h
@@ -1,4 +1,31 @@
+/*
+ * There are two expected ways of including this header.
+ *
+ * 1) The "default" case (expected from tools etc).
+ *
+ * Simply #include <public/errno.h>
+ *
+ * In this circumstance, normal header guards apply and the includer shall get
+ * an enumeration in the XEN_xxx namespace, appropriate for C or assembly.
+ *
+ * 2) The special case where the includer provides a XEN_ERRNO() in scope.
+ *
+ * In this case, no inclusion guards apply and the caller is responsible for
+ * their XEN_ERRNO() being appropriate in the included context.  The header
+ * will unilaterally #undef XEN_ERRNO().
+ */
+
+#ifndef XEN_ERRNO
+
+/*
+ * Includer has not provided a custom XEN_ERRNO().  Arrange for normal header
+ * guards, an automatic enum (for C code) and constants in the XEN_xxx
+ * namespace.
+ */
 #ifndef __XEN_PUBLIC_ERRNO_H__
+#define __XEN_PUBLIC_ERRNO_H__
+
+#define XEN_ERRNO_DEFAULT_INCLUDE
 
 #ifndef __ASSEMBLY__
 
@@ -11,11 +38,12 @@ enum xen_errno {
 
 #endif /* __ASSEMBLY__ */
 
+#endif /* __XEN_PUBLIC_ERRNO_H__ */
+#endif /* !XEN_ERRNO */
+
 /* ` enum neg_errnoval {  [ -Efoo for each Efoo in the list below ]  } */
 /* ` enum errnoval { */
 
-#endif /* __XEN_PUBLIC_ERRNO_H__ */
-
 #ifdef XEN_ERRNO
 
 /*
@@ -84,14 +112,13 @@ XEN_ERRNO(ETIMEDOUT,	110)	/* Connection timed out */
 
 #undef XEN_ERRNO
 #endif /* XEN_ERRNO */
-
-#ifndef __XEN_PUBLIC_ERRNO_H__
-#define __XEN_PUBLIC_ERRNO_H__
-
 /* ` } */
 
+/* Clean up from a default include.  Close the enum (for C). */
+#ifdef XEN_ERRNO_DEFAULT_INCLUDE
+#undef XEN_ERRNO_DEFAULT_INCLUDE
 #ifndef __ASSEMBLY__
 };
 #endif
 
-#endif /*  __XEN_PUBLIC_ERRNO_H__ */
+#endif /* XEN_ERRNO_DEFAULT_INCLUDE */
diff --git a/xen/include/xen/errno.h b/xen/include/xen/errno.h
index 3178466..69b28dd 100644
--- a/xen/include/xen/errno.h
+++ b/xen/include/xen/errno.h
@@ -1,18 +1,16 @@
 #ifndef __XEN_ERRNO_H__
 #define __XEN_ERRNO_H__
 
-#include <public/errno.h>
-
 #ifndef __ASSEMBLY__
 
-#define XEN_ERRNO(name, value) name = XEN_##name,
+#define XEN_ERRNO(name, value) name = value,
 enum {
 #include <public/errno.h>
 };
 
 #else /* !__ASSEMBLY__ */
 
-#define XEN_ERRNO(name, value) .equ name, XEN_##name
+#define XEN_ERRNO(name, value) .equ name, value
 #include <public/errno.h>
 
 #endif /* __ASSEMBLY__ */
-- 
2.1.4


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