[PATCH RFC v4 3/6] virtio-net: assert header sizes

[Steffen Trumtrar]

The header is cast from skb->cb and from device buffers, so its layout
must not change silently. Add static_asserts for the offset of tstamp,
the total size, the alignment, and that the header fits into skb->cb.

Signed-off-by: Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx>
Assisted-by: Claude:claude-opus-5-5
---
 include/linux/virtio_net.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 2abd8a614a23f..e7776a37a486b 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -29,6 +29,17 @@ struct virtio_net_common_hdr {
 	__le16 tstamp[4];	/* le64 TAI receive time in ns, 0 if none */
 };
 
+/*
+ * The header is cast from skb->cb and from device buffers, the layout must not
+ * change silently.
+ */
+static_assert(offsetof(struct virtio_net_common_hdr, tstamp) == 32);
+static_assert(sizeof(struct virtio_net_common_hdr) ==
+	      offsetofend(struct virtio_net_common_hdr, tstamp));
+static_assert(__alignof__(struct virtio_net_common_hdr) == 2);
+/* virtio_net_common_hdr must fit into skb->cb */
+static_assert(sizeof(struct virtio_net_common_hdr) <= sizeof_field(struct sk_buff, cb));
+
 static inline bool virtio_net_hdr_match_proto(__be16 protocol, __u8 gso_type)
 {
 	switch (gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {

-- 
2.52.0