[PATCH RFC 1/7] watch_queue: Make watch_sizeof() check record size

[Gabriel Krisman Bertazi <krisman@collabora.com>]

From: David Howells <dhowells@redhat.com>

Make watch_sizeof() give a build error if the size of the struct won't fit
into the size field in the header.

Reported-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
[Rebase to 5.10]
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
---
 include/linux/watch_queue.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/watch_queue.h b/include/linux/watch_queue.h
index c994d1b2cdba..f1086d12cd03 100644
--- a/include/linux/watch_queue.h
+++ b/include/linux/watch_queue.h
@@ -120,7 +120,12 @@ static inline void remove_watch_list(struct watch_list *wlist, u64 id)
  * watch_sizeof - Calculate the information part of the size of a watch record,
  * given the structure size.
  */
-#define watch_sizeof(STRUCT) (sizeof(STRUCT) << WATCH_INFO_LENGTH__SHIFT)
+#define watch_sizeof(STRUCT) \
+	({								\
+		size_t max = WATCH_INFO_LENGTH >> WATCH_INFO_LENGTH__SHIFT; \
+		BUILD_BUG_ON(sizeof(STRUCT) > max);			\
+		sizeof(STRUCT) << WATCH_INFO_LENGTH__SHIFT;		\
+	})
 
 #else
 static inline int watch_queue_init(struct pipe_inode_info *pipe)
-- 
2.28.0