Introduce the scsi_status union

Introduce the scsi_status union, a data structure that will be used in the
next patches to replace SCSI status codes represented as an integer. The
'combined' member makes it easy to convert existing SCSI code. The
'status', 'msg', 'host' and 'driver' enable access of individual SCSI
status fields in a type-safe fashion.

Change 'int result;' into the following to enable converting one driver at
a time:

	union {
		int result;
		union scsi_status status;
	};

A later patch will remove the outer union and 'int result;'.

Also to enable converting one driver at a time, make scsi_status_is_good(),
status_byte(), msg_byte(), host_byte() and driver_byte() accept an int or
union scsi_status as argument. A later patch will make this function and
these macros accept the scsi_status union only.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: John Garry <john.garry@huawei.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>

drivers/scsi/scsi.c

@@ -763,10 +763,20 @@ MODULE_LICENSE("GPL");
 module_param(scsi_logging_level, int, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(scsi_logging_level, "a bit mask of logging levels");
 
+#define TEST_STATUS ((union scsi_status){.b = {				\
+			.driver = 1, .host = 2, .msg = 3, .status = 8}})
+
 static int __init init_scsi(void)
 {
 	int error;
 
+	BUILD_BUG_ON(sizeof(union scsi_status) != 4);
+	BUILD_BUG_ON(TEST_STATUS.combined != 0x01020308);
+	BUILD_BUG_ON(driver_byte(TEST_STATUS) != 1);
+	BUILD_BUG_ON(host_byte(TEST_STATUS) != 2);
+	BUILD_BUG_ON(msg_byte(TEST_STATUS) != 3);
+	BUILD_BUG_ON(status_byte(TEST_STATUS) != 4);
+
 	error = scsi_init_procfs();
 	if (error)
 		goto cleanup_queue;

include/linux/bsg-lib.h

@@ -11,6 +11,7 @@
 
 #include <linux/blkdev.h>
 #include <scsi/scsi_request.h>
+#include <scsi/scsi_status.h>
 
 struct request;
 struct device;
@@ -52,7 +53,10 @@ struct bsg_job {
 	struct bsg_buffer request_payload;
 	struct bsg_buffer reply_payload;
 
-	int result;
+	union {
+		int		  result; /* do not use in new code */
+		union scsi_status status;
+	};
 	unsigned int reply_payload_rcv_len;
 
 	/* BIDI support */

include/scsi/scsi.h

@@ -39,7 +39,7 @@ enum scsi_timeouts {
  * This returns true for known good conditions that may be treated as
  * command completed normally
  */
-static inline int scsi_status_is_good(int status)
+static inline bool __scsi_status_is_good(int status)
 {
 	/*
 	 * FIXME: bit0 is listed as reserved in SCSI-2, but is
@@ -56,6 +56,20 @@ static inline int scsi_status_is_good(int status)
 		(status == SAM_STAT_COMMAND_TERMINATED));
 }
 
+/*
+ * If the 'status' argument has type int, unsigned int or union scsi_status,
+ * return the combined SCSI status. If the 'status' argument has another type,
+ * trigger a compiler error by passing a struct to a context where an integer
+ * is expected.
+ */
+#define scsi_status_to_int(status)			\
+	__builtin_choose_expr(sizeof(status) == 4,	\
+			      *(int32_t *)&(status),	\
+			      (union scsi_status){})
+
+#define scsi_status_is_good(status)				\
+	__scsi_status_is_good(scsi_status_to_int(status))
+
 
 /*
  * standard mode-select header prepended to all mode-select commands
@@ -133,10 +147,10 @@ enum scsi_disposition {
  *      host_byte   = set by low-level driver to indicate status.
  *      driver_byte = set by mid-level.
  */
-#define status_byte(result) (((result) >> 1) & 0x7f)
-#define msg_byte(result)    (((result) >> 8) & 0xff)
-#define host_byte(result)   (((result) >> 16) & 0xff)
-#define driver_byte(result) (((result) >> 24) & 0xff)
+#define status_byte(result) ((scsi_status_to_int((result)) >> 1) & 0x7f)
+#define msg_byte(result)    ((scsi_status_to_int((result)) >> 8) & 0xff)
+#define host_byte(result)   ((scsi_status_to_int((result)) >> 16) & 0xff)
+#define driver_byte(result) ((scsi_status_to_int((result)) >> 24) & 0xff)
 
 #define sense_class(sense)  (((sense) >> 4) & 0x7)
 #define sense_error(sense)  ((sense) & 0xf)

include/scsi/scsi_bsg_iscsi.h

@@ -13,6 +13,7 @@
  */
 
 #include <scsi/scsi.h>
+#include <scsi/scsi_status.h>
 
 /*
  * iSCSI Transport SGIO v4 BSG Message Support
@@ -82,7 +83,10 @@ struct iscsi_bsg_reply {
 	 * msg and status fields. The per-msgcode reply structure
 	 * will contain valid data.
 	 */
-	uint32_t result;
+	union {
+		uint32_t	  result; /* do not use in new code */
+		union scsi_status status;
+	};
 
 	/* If there was reply_payload, how much was recevied ? */
 	uint32_t reply_payload_rcv_len;

include/scsi/scsi_cmnd.h

@@ -140,7 +140,11 @@ struct scsi_cmnd {
 					 * obtained by scsi_malloc is guaranteed
 					 * to be at an address < 16Mb). */
 
-	int result;		/* Status code from lower level driver */
+	/* Status code from lower level driver */
+	union {
+		int		  result; /* do not use in new code. */
+		union scsi_status status;
+	};
 	int flags;		/* Command flags */
 	unsigned long state;	/* Command completion state */
 
@@ -317,23 +321,23 @@ static inline struct scsi_data_buffer *scsi_prot(struct scsi_cmnd *cmd)
 static inline void set_status_byte(struct scsi_cmnd *cmd,
 				   enum sam_status status)
 {
-	cmd->result = (cmd->result & 0xffffff00) | status;
+	cmd->status.b.status = status;
 }
 
 static inline void set_msg_byte(struct scsi_cmnd *cmd, enum msg_byte status)
 {
-	cmd->result = (cmd->result & 0xffff00ff) | (status << 8);
+	cmd->status.b.msg = status;
 }
 
 static inline void set_host_byte(struct scsi_cmnd *cmd, enum host_status status)
 {
-	cmd->result = (cmd->result & 0xff00ffff) | (status << 16);
+	cmd->status.b.host = status;
 }
 
 static inline void set_driver_byte(struct scsi_cmnd *cmd,
 				   enum driver_status status)
 {
-	cmd->result = (cmd->result & 0x00ffffff) | (status << 24);
+	cmd->status.b.driver = status;
 }
 
 static inline unsigned scsi_transfer_length(struct scsi_cmnd *scmd)

include/scsi/scsi_eh.h

@@ -6,6 +6,8 @@
 
 #include <scsi/scsi_cmnd.h>
 #include <scsi/scsi_common.h>
+#include <scsi/scsi_status.h>
+
 struct scsi_device;
 struct Scsi_Host;
 
@@ -31,7 +33,10 @@ extern int scsi_ioctl_reset(struct scsi_device *, int __user *);
 
 struct scsi_eh_save {
 	/* saved state */
-	int result;
+	union {
+		int		  result; /* do not use in new code */
+		union scsi_status status;
+	};
 	unsigned int resid_len;
 	int eh_eflags;
 	enum dma_data_direction data_direction;

include/scsi/scsi_request.h

@@ -3,14 +3,18 @@
 #define _SCSI_SCSI_REQUEST_H
 
 #include <linux/blk-mq.h>
+#include <scsi/scsi_status.h>
 
 #define BLK_MAX_CDB	16
 
 struct scsi_request {
 	unsigned char	__cmd[BLK_MAX_CDB];
 	unsigned char	*cmd;
 	unsigned short	cmd_len;
-	int		result;
+	union {
+		int		  result; /* do not use in new code */
+		union scsi_status status;
+	};
 	unsigned int	sense_len;
 	unsigned int	resid_len;	/* residual count */
 	int		retries;

include/scsi/scsi_status.h

@@ -3,6 +3,7 @@
 
 #include <linux/types.h>
 #include <linux/compiler_attributes.h>
+#include <asm/byteorder.h>
 #include <scsi/scsi_proto.h>
 
 /*
@@ -88,4 +89,32 @@ enum driver_status {
 	DRIVER_SENSE	= 0x08,
 } __packed;
 
+/**
+ * SCSI status passed by LLDs to the midlayer.
+ * @combined: One of the following:
+ *	- A (driver, host, msg, status) quadruplet encoded as a 32-bit integer.
+ *	- A negative Unix error code.
+ *	- In the IDE code, a positive value that represents an error code, an
+ *	  error counter or a bitfield.
+ * @b: SCSI status code.
+ */
+union scsi_status {
+	int32_t combined;
+	struct {
+#if defined(__BIG_ENDIAN)
+		enum driver_status driver;
+		enum host_status host;
+		enum msg_byte msg;
+		enum sam_status status;
+#elif defined(__LITTLE_ENDIAN)
+		enum sam_status status;
+		enum msg_byte msg;
+		enum host_status host;
+		enum driver_status driver;
+#else
+#error Endianness?
+#endif
+	} b;
+};
+
 #endif /* _SCSI_SCSI_STATUS_H */

include/uapi/scsi/scsi_bsg_fc.h

@@ -9,6 +9,9 @@
 #define SCSI_BSG_FC_H
 
 #include <linux/types.h>
+#ifdef __KERNEL__
+#include <scsi/scsi_status.h>
+#endif
 
 /*
  * This file intended to be included by both kernel and user space
@@ -291,7 +294,14 @@ struct fc_bsg_reply {
 	 *    msg and status fields. The per-msgcode reply structure
 	 *    will contain valid data.
 	 */
+#ifdef __KERNEL__
+	union {
+		__u32		  result; /* do not use in new kernel code */
+		union scsi_status status;
+	};
+#else
 	__u32 result;
+#endif
 
 	/* If there was reply_payload, how much was recevied ? */
 	__u32 reply_payload_rcv_len;

include/uapi/scsi/scsi_bsg_ufs.h

@@ -9,6 +9,10 @@
 #define SCSI_BSG_UFS_H
 
 #include <linux/types.h>
+#ifdef __KERNEL__
+#include <scsi/scsi_status.h>
+#endif
+
 /*
  * This file intended to be included by both kernel and user space
  */
@@ -95,7 +99,14 @@ struct ufs_bsg_reply {
 	 * msg and status fields. The per-msgcode reply structure
 	 * will contain valid data.
 	 */
+#ifdef __KERNEL__
+	union {
+		__u32		  result; /* do not use in new kernel code */
+		union scsi_status status;
+	};
+#else
 	__u32 result;
+#endif
 
 	/* If there was reply_payload, how much was received? */
 	__u32 reply_payload_rcv_len;