[PATCH] tracing: Fix handling of TRANSFER LENGTH == 0 for READ(6) and WRITE(6)

[Bart Van Assche <bvanassche@acm.org>]

According to SBC-2 a TRANSFER LENGTH field of zero means that 256 logical
blocks must be transferred. Make the SCSI tracing code follow SBC-2.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Fixes: bf8162354233 ("[SCSI] add scsi trace core functions and put trace points")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/scsi_trace.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/scsi_trace.c b/drivers/scsi/scsi_trace.c
index 784ed9a32a0d..ac35c301c792 100644
--- a/drivers/scsi/scsi_trace.c
+++ b/drivers/scsi/scsi_trace.c
@@ -18,15 +18,18 @@ static const char *
 scsi_trace_rw6(struct trace_seq *p, unsigned char *cdb, int len)
 {
 	const char *ret = trace_seq_buffer_ptr(p);
-	sector_t lba = 0, txlen = 0;
+	u32 lba = 0, txlen;
 
 	lba |= ((cdb[1] & 0x1F) << 16);
 	lba |=  (cdb[2] << 8);
 	lba |=   cdb[3];
-	txlen = cdb[4];
+	/*
+	 * From SBC-2: a TRANSFER LENGTH field set to zero specifies that 256
+	 * logical blocks shall be read (READ(6)) or written (WRITE(6)).
+	 */
+	txlen = cdb[4] ? cdb[4] : 256;
 
-	trace_seq_printf(p, "lba=%llu txlen=%llu",
-			 (unsigned long long)lba, (unsigned long long)txlen);
+	trace_seq_printf(p, "lba=%u txlen=%u", lba, txlen);
 	trace_seq_putc(p, 0);
 
 	return ret;
-- 
2.24.0.rc1.363.gb1bccd3e3d-goog