[SCSI] st: add st_scsi_kern_execute helper function

st_scsi_kern_execute is a helper function to perform SCSI commands
synchronously. It supports data transfer with a liner in-kernel buffer
(not scatter gather). st_scsi_kern_execute internally uses
scsi_execute().

The majority of st_do_scsi can be replaced with
st_scsi_kern_execute. This is a preparation for rewriting st_do_scsi
to remove obsolete scsi_execute_async().

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/st.c

@@ -533,6 +533,28 @@ st_do_scsi(struct st_request * SRpnt, struct scsi_tape * STp, unsigned char *cmd
 	return SRpnt;
 }
 
+static int st_scsi_kern_execute(struct st_request *streq,
+				const unsigned char *cmd, int data_direction,
+				void *buffer, unsigned bufflen, int timeout,
+				int retries)
+{
+	struct scsi_tape *stp = streq->stp;
+	int ret, resid;
+
+	stp->buffer->cmdstat.have_sense = 0;
+	memcpy(streq->cmd, cmd, sizeof(streq->cmd));
+
+	ret = scsi_execute(stp->device, cmd, data_direction, buffer, bufflen,
+			   streq->sense, timeout, retries, 0, &resid);
+	if (driver_byte(ret) & DRIVER_ERROR)
+		return -EBUSY;
+
+	stp->buffer->cmdstat.midlevel_result = streq->result = ret;
+	stp->buffer->cmdstat.residual = resid;
+	stp->buffer->syscall_result = st_chk_result(stp, streq);
+
+	return 0;
+}
 
 /* Handle the write-behind checking (waits for completion). Returns -ENOSPC if
    write has been correct but EOM early warning reached, -EIO if write ended in