Re: [PATCH][next] net/smc: Use static_assert() to check struct sizes

[Jan Karcher]

On 09/08/2024 00:07, Gustavo A. R. Silva wrote:

Commit 9748dbc9f265 ("net/smc: Avoid -Wflex-array-member-not-at-end
warnings") introduced tagged `struct smc_clc_v2_extension_fixed` and
`struct smc_clc_smcd_v2_extension_fixed`. We want to ensure that when
new members need to be added to the flexible structures, they are
always included within these tagged structs.

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.

Read up what the macro does. I like it.
Compile tested on s390.

Reviewed-by: Jan Karcher <j...@linux.ibm.com>

Signed-off-by: Gustavo A. R. Silva <gustavo...@kernel.org>
---
  net/smc/smc_clc.h | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/net/smc/smc_clc.h b/net/smc/smc_clc.h
index 467effb50cd6..5625fda2960b 100644
--- a/net/smc/smc_clc.h
+++ b/net/smc/smc_clc.h
@@ -145,6 +145,8 @@ struct smc_clc_v2_extension {
        );
        u8 user_eids[][SMC_MAX_EID_LEN];
  };
+static_assert(offsetof(struct smc_clc_v2_extension, user_eids) == 
sizeof(struct smc_clc_v2_extension_fixed),
+             "struct member likely outside of struct_group_tagged()");

struct smc_clc_msg_proposal_prefix { /* prefix part of clc proposal message*/

        __be32 outgoing_subnet; /* subnet mask */
@@ -169,6 +171,8 @@ struct smc_clc_smcd_v2_extension {
        );
        struct smc_clc_smcd_gid_chid gidchid[];
  };
+static_assert(offsetof(struct smc_clc_smcd_v2_extension, gidchid) == 
sizeof(struct smc_clc_smcd_v2_extension_fixed),
+             "struct member likely outside of struct_group_tagged()");

struct smc_clc_msg_proposal { /* clc proposal message sent by Linux */

        struct smc_clc_msg_hdr hdr;