On Fri, Apr 05, 2019 at 06:04:21PM +0200, Peter Krempa wrote:
With the introduction of more and more internal data types which support VIR_AUTOPTR it's becoming common to see the following pattern: VIR_AUTOPTR(virSomething) some = NULL virSomethingPtr ret = NULL; ... (ret is not touched ) ... VIR_STEAL_PTR(ret, some); return ret; This patch introduces a macro named VIR_RETURN_PTR which returns the pointer directly without the need for an explicitly defined return variable and use of VIR_STEAL_PTR. Internally obviously a temporary pointer is created to allow setting the original pointer to NULL so that the VIR_AUTOPTR function does not free the memory which we want to actually return. The name of the temporary variable is deliberately long and complex to minimize the possibility of collision.
Both my gcc and clang warn in that case:
conf/domain_conf.c:2209:5: error: declaration shadows a local variable [-Werror,-Wshadow]
VIR_RETURN_PTR(virTemporaryReturnPointer);
^
./internal.h:292:21: note: expanded from macro 'VIR_RETURN_PTR'
typeof(ptr) virTemporaryReturnPointer = (ptr); \
^
conf/domain_conf.c:2199:26: note: previous declaration is here
virDomainVsockDefPtr virTemporaryReturnPointer = NULL;
^
Signed-off-by: Peter Krempa <pkrempa@xxxxxxxxxx>
---
src/internal.h | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/src/internal.h b/src/internal.h
index cf03a82105..5a868bb00c 100644
--- a/src/internal.h
+++ b/src/internal.h
@@ -279,6 +279,21 @@
(b) = NULL; \
} while (0)
+/**
+ * VIR_RETURN_PTR:
+ * @ret: pointer to return
+ *
+ * Returns value of @ret while clearing @ret. This ensures that pointers
+ * freed by using VIR_AUTOPTR can be easily passed back to the caller without
+ * any temporary variable. @ptr is evaluated more than once.
+ */
+# define VIR_RETURN_PTR(ptr) \
+ do { \
+ typeof(ptr) virTemporaryReturnPointer = (ptr); \
+ (ptr) = NULL; \
+ return virTemporaryReturnPointer; \
+ } while (0)
+
/**
Reviewed-by: Ján Tomko <jtomko@xxxxxxxxxx> Jano
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