From: David Laight <[email protected]>
Autoterminating nested for() loops can be used inside #defines to
declare variables that are scoped to the statement that follows.
These are used by __scoped_user_access() but may have other uses
and the gory details are best separated from the use.
Using 'with (declaration)' and 'and_with (declaration)' seems to
read reasonably well and doesn't seem to collide with any existing
code.
As an example the scoped user access definition becomes:
with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size,
elbl)) \
/* Force modified pointer usage within the scope */
\
and_with (const auto uptr __cleanup(...) = _tmpptr)
Signed-off-by: David Laight <[email protected]>
---
include/linux/compiler.h | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index af16624b29fd..1098a91b5591 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -369,6 +369,32 @@ static inline void *offset_to_ptr(const int *off)
*/
#define prevent_tail_call_optimization() mb()
+/*
+ * Sometimes a #define needs to declare a variable that is scoped
+ * to the statement that follows without having mismatched {}.
+ * with (int x = expression) {
+ * statements
+ * }
+ * is the same as:
+ * {
+ * int x = expression;
+ * statements
+ * }
+ * but lets it all be hidden from the call site, eg:
+ * frobnicate(x, args) {
+ * statements
+ * }
+ * Only a single variable can be defined, and_with() allows extra ones
+ * without adding an additional outer loop.
+ *
+ * The controlled scope can be terminated using return, break, continue or
goto.
+ */
+#define with(declaration) \
+ for (bool _with_done = false; !_with_done; _with_done = true) \
+ and_with (declaration)
+#define and_with(declaration) \
+ for (declaration; !_with_done; _with_done = true)
+
#include <asm/rwonce.h>
#endif /* __LINUX_COMPILER_H */
--
2.39.5
