[PATCH][next] smb: smb2pdu.h: Use static_assert() to check struct sizes

[Gustavo A. R. Silva]

Commit 9f9bef9bc5c6 ("smb: smb2pdu.h: Avoid -Wflex-array-member-not-at-end
warnings") introduced tagged `struct create_context_hdr`. We want to
ensure that when new members need to be added to the flexible structure,
they are always included within this tagged struct.

So, we use `static_assert()` to ensure that the memory layout for
both the flexible structure and the tagged struct is the same after
any changes.

Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
---
 fs/smb/common/smb2pdu.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/smb/common/smb2pdu.h b/fs/smb/common/smb2pdu.h
index c3ee42188d25..c769f9dbc0b4 100644
--- a/fs/smb/common/smb2pdu.h
+++ b/fs/smb/common/smb2pdu.h
@@ -1216,6 +1216,8 @@ struct create_context {
 	);
 	__u8 Buffer[];
 } __packed;
+static_assert(offsetof(struct create_context, Buffer) == sizeof(struct create_context_hdr),
+	      "struct member likely outside of __struct_group()");
 
 struct smb2_create_req {
 	struct smb2_hdr hdr;
-- 
2.34.1