scsi_debug: simple short transfer injection

Add an option to only transfer half the data for every n-th command.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/scsi/scsi_debug.c

@@ -130,6 +130,7 @@ static const char * scsi_debug_version_date = "20100324";
 #define SCSI_DEBUG_OPT_DIF_ERR   32
 #define SCSI_DEBUG_OPT_DIX_ERR   64
 #define SCSI_DEBUG_OPT_MAC_TIMEOUT  128
+#define SCSI_DEBUG_OPT_SHORT_TRANSFER	256
 /* When "every_nth" > 0 then modulo "every_nth" commands:
  *   - a no response is simulated if SCSI_DEBUG_OPT_TIMEOUT is set
  *   - a RECOVERED_ERROR is simulated on successful read and write
@@ -3583,6 +3584,7 @@ int scsi_debug_queuecommand_lck(struct scsi_cmnd *SCpnt, done_funct_t done)
 	int inj_transport = 0;
 	int inj_dif = 0;
 	int inj_dix = 0;
+	int inj_short = 0;
 	int delay_override = 0;
 	int unmap = 0;
 
@@ -3628,6 +3630,8 @@ int scsi_debug_queuecommand_lck(struct scsi_cmnd *SCpnt, done_funct_t done)
 			inj_dif = 1; /* to reads and writes below */
 		else if (SCSI_DEBUG_OPT_DIX_ERR & scsi_debug_opts)
 			inj_dix = 1; /* to reads and writes below */
+		else if (SCSI_DEBUG_OPT_SHORT_TRANSFER & scsi_debug_opts)
+			inj_short = 1;
 	}
 
 	if (devip->wlun) {
@@ -3744,6 +3748,10 @@ int scsi_debug_queuecommand_lck(struct scsi_cmnd *SCpnt, done_funct_t done)
 		if (scsi_debug_fake_rw)
 			break;
 		get_data_transfer_info(cmd, &lba, &num, &ei_lba);
+
+		if (inj_short)
+			num /= 2;
+
 		errsts = resp_read(SCpnt, lba, num, devip, ei_lba);
 		if (inj_recovered && (0 == errsts)) {
 			mk_sense_buffer(devip, RECOVERED_ERROR,