scsi: megaraid: Stop using the SCSI pointer

Set .cmd_size in the SCSI host template instead of using the SCSI pointer
from struct scsi_cmnd. This patch prepares for removal of the SCSI pointer
from struct scsi_cmnd.

Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Johannes Thumshirn <[e-mail]>
Reviewed-by: Himanshu Madhani <[e-mail]>
Signed-off-by: Bart Van Assche <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/megaraid.c

···
 static void
 mega_rundoneq (adapter_t *adapter)
 {
-	struct scsi_cmnd *cmd;
-	struct list_head *pos;
+	struct megaraid_cmd_priv *cmd_priv;
 
-	list_for_each(pos, &adapter->completed_list) {
-
-		struct scsi_pointer* spos = (struct scsi_pointer *)pos;
-
-		cmd = list_entry(spos, struct scsi_cmnd, SCp);
-		scsi_done(cmd);
-	}
+	list_for_each_entry(cmd_priv, &adapter->completed_list, entry)
+		scsi_done(megaraid_to_scsi_cmd(cmd_priv));
 
 	INIT_LIST_HEAD(&adapter->completed_list);
 }
···
 	.eh_bus_reset_handler		= megaraid_reset,
 	.eh_host_reset_handler		= megaraid_reset,
 	.no_write_same			= 1,
+	.cmd_size			= sizeof(struct megaraid_cmd_priv),
 };
 
 static int

drivers/scsi/megaraid.h

···
 
 #include <linux/spinlock.h>
 #include <linux/mutex.h>
+#include <scsi/scsi_cmnd.h>
 
 #define MEGARAID_VERSION	\
 	"v2.00.4 (Release Date: Thu Feb 9 08:51:30 EST 2006)\n"
···
 #define CACHED_IO		0
 #define DIRECT_IO		1
 
+struct megaraid_cmd_priv {
+	struct list_head entry;
+};
 
-#define SCSI_LIST(scp) ((struct list_head *)(&(scp)->SCp))
+#define SCSI_LIST(scp)							\
+	(&((struct megaraid_cmd_priv *)scsi_cmd_priv(scp))->entry)
+
+struct scsi_cmd_and_priv {
+	struct scsi_cmnd	 cmd;
+	struct megaraid_cmd_priv priv;
+};
+
+static inline struct scsi_cmnd *
+megaraid_to_scsi_cmd(struct megaraid_cmd_priv *cmd_priv)
+{
+	/* See also scsi_mq_setup_tags() */
+	BUILD_BUG_ON(sizeof(struct scsi_cmd_and_priv) !=
+		     sizeof(struct scsi_cmnd) +
+		     sizeof(struct megaraid_cmd_priv));
+
+	return &container_of(cmd_priv, struct scsi_cmd_and_priv, priv)->cmd;
+}
 
 /*
  * Each controller's soft state