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[01/24] scsi: core: Make scsi_cmd_to_rq() accept const arguments

Message ID 20250403211937.2225615-2-bvanassche@acm.org
State New
Headers show
Series Optimize the hot path in the UFS driver | expand

Commit Message

Bart Van Assche April 3, 2025, 9:17 p.m. UTC 
Instead of requiring the caller to cast away constness, make
scsi_cmd_to_rq() accept const arguments.

Cc: Hannes Reinecke <hare@suse.de>
Cc: John Garry <john.g.garry@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/scsi_logging.c | 10 +++++-----
 include/scsi/scsi_cmnd.h    |  9 +++++----
 2 files changed, 10 insertions(+), 9 deletions(-)

Comments

Bart Van Assche April 4, 2025, 4:23 p.m. UTC | #1 
On 4/4/25 3:39 AM, John Garry wrote:
> On 03/04/2025 22:17, Bart Van Assche wrote:
>>   /* Variant of blk_mq_rq_from_pdu() that verifies the type of its 
>> argument. */
>> -static inline struct request *scsi_cmd_to_rq(struct scsi_cmnd *scmd)
>> -{
>> -    return blk_mq_rq_from_pdu(scmd);
>> -}
>> +#define scsi_cmd_to_rq(scmd)                                       \
>> +    _Generic(scmd,                                             \
>> +        const struct scsi_cmnd *: (const struct request *) \
>> +            blk_mq_rq_from_pdu((void *)scmd),          \
>> +        struct scsi_cmnd *: blk_mq_rq_from_pdu((void *)scmd))
>>   /*
> 
> Out of curiosity, how this that better than this:
> 
> static inline struct request *scsi_cmd_to_rq(const struct scsi_cmnd *scmd)
> {
>      return blk_mq_rq_from_pdu((void *)scmd);
> }

Yikes. With the inline function variant constness can be removed
silently as follows:

     const struct scsi_cmnd *scmd;
     struct request *rq = scsi_cmd_to_rq(scmd);

With patch 01/24, the compiler will issue a warning for the above code.

Bart.
diff mbox series

Patch

diff --git a/drivers/scsi/scsi_logging.c b/drivers/scsi/scsi_logging.c
index b02af340c2d3..5aaff629b999 100644
--- a/drivers/scsi/scsi_logging.c
+++ b/drivers/scsi/scsi_logging.c
@@ -28,7 +28,7 @@  static void scsi_log_release_buffer(char *bufptr)
 
 static inline const char *scmd_name(const struct scsi_cmnd *scmd)
 {
-	struct request *rq = scsi_cmd_to_rq((struct scsi_cmnd *)scmd);
+	const struct request *rq = scsi_cmd_to_rq(scmd);
 
 	if (!rq->q || !rq->q->disk)
 		return NULL;
@@ -94,7 +94,7 @@  void scmd_printk(const char *level, const struct scsi_cmnd *scmd,
 	if (!logbuf)
 		return;
 	off = sdev_format_header(logbuf, logbuf_len, scmd_name(scmd),
-				 scsi_cmd_to_rq((struct scsi_cmnd *)scmd)->tag);
+				 scsi_cmd_to_rq(scmd)->tag);
 	if (off < logbuf_len) {
 		va_start(args, fmt);
 		off += vscnprintf(logbuf + off, logbuf_len - off, fmt, args);
@@ -374,8 +374,8 @@  EXPORT_SYMBOL(__scsi_print_sense);
 void scsi_print_sense(const struct scsi_cmnd *cmd)
 {
 	scsi_log_print_sense(cmd->device, scmd_name(cmd),
-			     scsi_cmd_to_rq((struct scsi_cmnd *)cmd)->tag,
-			     cmd->sense_buffer, SCSI_SENSE_BUFFERSIZE);
+			     scsi_cmd_to_rq(cmd)->tag, cmd->sense_buffer,
+			     SCSI_SENSE_BUFFERSIZE);
 }
 EXPORT_SYMBOL(scsi_print_sense);
 
@@ -393,7 +393,7 @@  void scsi_print_result(const struct scsi_cmnd *cmd, const char *msg,
 		return;
 
 	off = sdev_format_header(logbuf, logbuf_len, scmd_name(cmd),
-				 scsi_cmd_to_rq((struct scsi_cmnd *)cmd)->tag);
+				 scsi_cmd_to_rq(cmd)->tag);
 
 	if (off >= logbuf_len)
 		goto out_printk;
diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index 8ecfb94049db..154fbb39ca0c 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -144,10 +144,11 @@  struct scsi_cmnd {
 };
 
 /* Variant of blk_mq_rq_from_pdu() that verifies the type of its argument. */
-static inline struct request *scsi_cmd_to_rq(struct scsi_cmnd *scmd)
-{
-	return blk_mq_rq_from_pdu(scmd);
-}
+#define scsi_cmd_to_rq(scmd)                                       \
+	_Generic(scmd,                                             \
+		const struct scsi_cmnd *: (const struct request *) \
+			blk_mq_rq_from_pdu((void *)scmd),          \
+		struct scsi_cmnd *: blk_mq_rq_from_pdu((void *)scmd))
 
 /*
  * Return the driver private allocation behind the command.