[PATCH v2 5/5] mm: add the __must_check attribute to {gfn,mfn,dfn}_add()

[Roger Pau Monne <roger.pau@citrix.com>]

It's not obvious from just the function name whether the incremented value will
be stored in the parameter, or returned to the caller.  That has leads to bugs
in the past as callers may assume the incremented value is stored in the
parameter.

Add the __must_check attribute to the function to easily spot callers that
don't consume the returned value, which signals an error in the caller logic.

No functional change intended.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Julien Grall <jgrall@amazon.com>
---
Changes since v1:
 - Also add attribute to dfn_add().
---
 xen/include/xen/iommu.h    | 2 +-
 xen/include/xen/mm-frame.h | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
index 7aa6a7720977..9621459c63ee 100644
--- a/xen/include/xen/iommu.h
+++ b/xen/include/xen/iommu.h
@@ -42,7 +42,7 @@ TYPE_SAFE(uint64_t, dfn);
 #undef dfn_x
 #endif
 
-static inline dfn_t dfn_add(dfn_t dfn, unsigned long i)
+static inline dfn_t __must_check dfn_add(dfn_t dfn, unsigned long i)
 {
     return _dfn(dfn_x(dfn) + i);
 }
diff --git a/xen/include/xen/mm-frame.h b/xen/include/xen/mm-frame.h
index 922ae418807a..c25e836f255a 100644
--- a/xen/include/xen/mm-frame.h
+++ b/xen/include/xen/mm-frame.h
@@ -23,7 +23,7 @@ TYPE_SAFE(unsigned long, mfn);
 #undef mfn_x
 #endif
 
-static inline mfn_t mfn_add(mfn_t mfn, unsigned long i)
+static inline mfn_t __must_check mfn_add(mfn_t mfn, unsigned long i)
 {
     return _mfn(mfn_x(mfn) + i);
 }
@@ -62,7 +62,7 @@ TYPE_SAFE(unsigned long, gfn);
 #undef gfn_x
 #endif
 
-static inline gfn_t gfn_add(gfn_t gfn, unsigned long i)
+static inline gfn_t __must_check gfn_add(gfn_t gfn, unsigned long i)
 {
     return _gfn(gfn_x(gfn) + i);
 }
-- 
2.43.0