scsi: fc: Avoid -Wflex-array-member-not-at-end warnings

-Wflex-array-member-not-at-end has been introduced in GCC-14, and we are
getting ready to enable it, globally.

So, in order to avoid ending up with a flexible-array member in the
middle of multiple other structs, we use the '__struct_group()' helper
to create a new tagged 'struct fc_df_desc_fpin_reg_hdr'.  This structure
groups together all the members of the flexible 'struct
fc_df_desc_fpin_reg' except the flexible array.

As a result, the array is effectively separated from the rest of the
members without modifying the memory layout of the flexible structure.
We then change the type of the middle struct members currently causing
trouble from 'struct fc_df_desc_fpin_reg' to 'struct
fc_df_desc_fpin_reg_hdr'.

We also want to ensure that in case new members need to be added to the
flexible structure, they are always included within the newly created
tagged struct. For this, we use '_Static_assert()'. This ensures that
the memory layout for both the flexible structure and the new tagged
struct is the same after any changes.

This approach avoids having to implement 'struct fc_df_desc_fpin_reg_hdr'
as a completely separate structure, thus preventing having to maintain
two independent but basically identical structures, closing the door
to potential bugs in the future.

The above is also done for flexible structures 'struct fc_els_rdf' and
'struct fc_els_rdf_resp'

So, with these changes, fix the following warnings:
drivers/scsi/lpfc/lpfc_hw4.h:4936:41: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/scsi/lpfc/lpfc_hw4.h:4942:41: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/scsi/lpfc/lpfc_hw4.h:4947:41: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/aK6hbQLyQlvlySf8@kspp
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Justin Tee <justin.tee@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

2 files changed, 4 insertions, 4 deletions

diff --git a/drivers/scsi/lpfc/lpfc_els.c b/drivers/scsi/lpfc/lpfc_els.c
index fca81e0c7c2e..432761fb49de 100644
--- a/drivers/scsi/lpfc/lpfc_els.c
+++ b/drivers/scsi/lpfc/lpfc_els.c
@@ -3762,7 +3762,7 @@ lpfc_issue_els_rdf(struct lpfc_vport *vport, uint8_t retry)
 	memset(prdf, 0, cmdsize);
 	prdf->rdf.fpin_cmd = ELS_RDF;
 	prdf->rdf.desc_len = cpu_to_be32(sizeof(struct lpfc_els_rdf_req) -
-					 sizeof(struct fc_els_rdf));
+					 sizeof(struct fc_els_rdf_hdr));
 	prdf->reg_d1.reg_desc.desc_tag = cpu_to_be32(ELS_DTAG_FPIN_REGISTER);
 	prdf->reg_d1.reg_desc.desc_len = cpu_to_be32(
 				FC_TLV_DESC_LENGTH_FROM_SZ(prdf->reg_d1));
diff --git a/drivers/scsi/lpfc/lpfc_hw4.h b/drivers/scsi/lpfc/lpfc_hw4.h
index bc709786e6af..a7f7ed86d2b0 100644
--- a/drivers/scsi/lpfc/lpfc_hw4.h
+++ b/drivers/scsi/lpfc/lpfc_hw4.h
@@ -4909,18 +4909,18 @@ struct send_frame_wqe {
 
 #define ELS_RDF_REG_TAG_CNT		4
 struct lpfc_els_rdf_reg_desc {
-	struct fc_df_desc_fpin_reg	reg_desc;	/* descriptor header */
+	struct fc_df_desc_fpin_reg_hdr	reg_desc;	/* descriptor header */
 	__be32				desc_tags[ELS_RDF_REG_TAG_CNT];
 							/* tags in reg_desc */
 };
 
 struct lpfc_els_rdf_req {
-	struct fc_els_rdf		rdf;	   /* hdr up to descriptors */
+	struct fc_els_rdf_hdr		rdf;	   /* hdr up to descriptors */
 	struct lpfc_els_rdf_reg_desc	reg_d1;	/* 1st descriptor */
 };
 
 struct lpfc_els_rdf_rsp {
-	struct fc_els_rdf_resp		rdf_resp;  /* hdr up to descriptors */
+	struct fc_els_rdf_resp_hdr	rdf_resp;  /* hdr up to descriptors */
 	struct lpfc_els_rdf_reg_desc	reg_d1;	/* 1st descriptor */
 };