To avoid compilers complainig about ambigious else blocks when putting
an if condition into a for_each macro one needs to invert the
condition and add a dummy else. We have a nice little convenience
macro for that in drm headers, let's move it out. Subsequent patches
will roll it out to other places.
The issue the compilers complain about are nested if with an else
block and no {} to disambiguate which if the else belongs to. The C
standard is clear, but in practice people forget:
if (foo)
if (bar)
/* something */
else
/* something else
The same can happen in a for_each macro when it also contains an if
condition at the end, except the compiler message is now really
confusing since there's only 1 if:
for_each_something()
if (bar)
/* something */
else
/* something else
The for_each_if() macro, by inverting the condition and adding an
else, avoids the compiler warning.
Motivated by a discussion with Andy and Yisheng, who want to add
another for_each_macro which would benefit from for_each_if() instead
of hand-rolling it.
Cc: Gustavo Padovan <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Sean Paul <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: NeilBrown <[email protected]>
Cc: Wei Wang <[email protected]>
Cc: Stefan Agner <[email protected]>
Cc: Andrei Vagin <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Yisheng Xie <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
--
v2: Explain a bit better what this is good for, after the discussion
with Peter Z.
---
include/drm/drmP.h | 3 ---
include/linux/kernel.h | 3 +++
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index f7a19c2a7a80..05350424a4d3 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -110,7 +110,4 @@ static inline bool drm_can_sleep(void)
return true;
}
-/* helper for handling conditionals in various for_each macros */
-#define for_each_if(condition) if (!(condition)) {} else
-
#endif
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 941dc0a5a877..4cb95ab9a5bc 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -71,6 +71,9 @@
*/
#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
+/* helper for handling conditionals in various for_each macros */
+#define for_each_if(condition) if (!(condition)) {} else
+
#define u64_to_user_ptr(x) ( \
{ \
typecheck(u64, x); \
--
2.18.0
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