RDMA/srp: Apply the __packed attribute to members instead of structures

Applying the __packed attribute to an entire data structure results in
suboptimal code on architectures that do not support unaligned accesses.
Hence apply the __packed attribute only to those data members that are
not naturally aligned.

Link: https://lore.kernel.org/r/[email protected]
Cc: Nicolas Morey-Chaisemartin <[email protected]>
Signed-off-by: Bart Van Assche <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: bvanassche

include/scsi/srp.h

@@ -107,10 +107,10 @@ struct srp_direct_buf {
  * having the 20-byte structure padded to 24 bytes on 64-bit architectures.
  */
 struct srp_indirect_buf {
-	struct srp_direct_buf	table_desc;
+	struct srp_direct_buf	table_desc __packed __aligned(4);
 	__be32			len;
-	struct srp_direct_buf	desc_list[];
-} __attribute__((packed));
+	struct srp_direct_buf	desc_list[] __packed __aligned(4);
+};
 
 /* Immediate data buffer descriptor as defined in SRP2. */
 struct srp_imm_buf {
@@ -175,13 +175,13 @@ struct srp_login_rsp {
 	u8	opcode;
 	u8	reserved1[3];
 	__be32	req_lim_delta;
-	u64	tag;
+	u64	tag __packed __aligned(4);
 	__be32	max_it_iu_len;
 	__be32	max_ti_iu_len;
 	__be16	buf_fmt;
 	u8	rsp_flags;
 	u8	reserved2[25];
-} __attribute__((packed));
+};
 
 struct srp_login_rej {
 	u8	opcode;
@@ -207,10 +207,6 @@ struct srp_t_logout {
 	u64	tag;
 };
 
-/*
- * We need the packed attribute because the SRP spec only aligns the
- * 8-byte LUN field to 4 bytes.
- */
 struct srp_tsk_mgmt {
 	u8	opcode;
 	u8	sol_not;
@@ -225,10 +221,6 @@ struct srp_tsk_mgmt {
 	u8	reserved5[8];
 };
 
-/*
- * We need the packed attribute because the SRP spec only aligns the
- * 8-byte LUN field to 4 bytes.
- */
 struct srp_cmd {
 	u8	opcode;
 	u8	sol_not;
@@ -266,7 +258,7 @@ struct srp_rsp {
 	u8	sol_not;
 	u8	reserved1[2];
 	__be32	req_lim_delta;
-	u64	tag;
+	u64	tag __packed __aligned(4);
 	u8	reserved2[2];
 	u8	flags;
 	u8	status;
@@ -275,7 +267,7 @@ struct srp_rsp {
 	__be32	sense_data_len;
 	__be32	resp_data_len;
 	u8	data[];
-} __attribute__((packed));
+};
 
 struct srp_cred_req {
 	u8	opcode;
@@ -301,13 +293,13 @@ struct srp_aer_req {
 	u8	sol_not;
 	u8	reserved[2];
 	__be32	req_lim_delta;
-	u64	tag;
+	u64	tag __packed __aligned(4);
 	u32	reserved2;
 	struct scsi_lun	lun;
 	__be32	sense_data_len;
 	u32	reserved3;
 	u8	sense_data[];
-} __attribute__((packed));
+};
 
 struct srp_aer_rsp {
 	u8	opcode;