[SCSI] st: show options currently set in sysfs

Show the current binary tape driver and mode options is sysfs. A file
(options) is created in each directory in /sys/class/scsi_tape. The files
contain masks showing the options. The mask bit definitions are the same as
used when setting the options using the MTSETDRVBUFFER function in the
MTIOCTOP ioctl (defined in include/linux/mtio.h). For example:
> cat /sys/class/scsi_tape/nst0/options
0x00000d07

[jejb: updated doc with correction from Randy Dunlap]
Signed-off-by: Kai Makisara <kai.makisara@kolumbus.fi>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

Documentation/scsi/st.txt

@@ -2,7 +2,7 @@ This file contains brief information about the SCSI tape driver.
 The driver is currently maintained by Kai Mäkisara (email
 Kai.Makisara@kolumbus.fi)
 
-Last modified: Thu Feb 21 21:54:16 2008 by kai.makisara
+Last modified: Sun Feb 24 21:59:07 2008 by kai.makisara
 
 
 BASICS
@@ -133,6 +133,11 @@ the defaults set by the user. The value -1 means the default is not set. The
 file 'dev' contains the device numbers corresponding to this device. The links
 'device' and 'driver' point to the SCSI device and driver entries.
 
+Each directory also contains the entry 'options' which shows the currently
+enabled driver and mode options. The value in the file is a bit mask where the
+bit definitions are the same as those used with MTSETDRVBUFFER in setting the
+options.
+
 A link named 'tape' is made from the SCSI device directory to the class
 directory corresponding to the mode 0 auto-rewind device (e.g., st0). 
 

drivers/scsi/st.c

@@ -4365,6 +4365,46 @@ static ssize_t st_defcompression_show(struct class_device *class_dev, char *buf)
 
 CLASS_DEVICE_ATTR(default_compression, S_IRUGO, st_defcompression_show, NULL);
 
+static ssize_t st_options_show(struct class_device *class_dev, char *buf)
+{
+	struct st_modedef *STm = (struct st_modedef *)class_get_devdata(class_dev);
+	struct scsi_tape *STp;
+	int i, j, options;
+	ssize_t l = 0;
+
+	for (i=0; i < st_dev_max; i++) {
+		for (j=0; j < ST_NBR_MODES; j++)
+			if (&scsi_tapes[i]->modes[j] == STm)
+				break;
+		if (j < ST_NBR_MODES)
+			break;
+	}
+	if (i == st_dev_max)
+		return 0;  /* should never happen */
+
+	STp = scsi_tapes[i];
+
+	options = STm->do_buffer_writes ? MT_ST_BUFFER_WRITES : 0;
+	options |= STm->do_async_writes ? MT_ST_ASYNC_WRITES : 0;
+	options |= STm->do_read_ahead ? MT_ST_READ_AHEAD : 0;
+	DEB( options |= debugging ? MT_ST_DEBUGGING : 0 );
+	options |= STp->two_fm ? MT_ST_TWO_FM : 0;
+	options |= STp->fast_mteom ? MT_ST_FAST_MTEOM : 0;
+	options |= STm->defaults_for_writes ? MT_ST_DEF_WRITES : 0;
+	options |= STp->can_bsr ? MT_ST_CAN_BSR : 0;
+	options |= STp->omit_blklims ? MT_ST_NO_BLKLIMS : 0;
+	options |= STp->can_partitions ? MT_ST_CAN_PARTITIONS : 0;
+	options |= STp->scsi2_logical ? MT_ST_SCSI2LOGICAL : 0;
+	options |= STm->sysv ? MT_ST_SYSV : 0;
+	options |= STp->immediate ? MT_ST_NOWAIT : 0;
+	options |= STp->sili ? MT_ST_SILI : 0;
+
+	l = snprintf(buf, PAGE_SIZE, "0x%08x\n", options);
+	return l;
+}
+
+CLASS_DEVICE_ATTR(options, S_IRUGO, st_options_show, NULL);
+
 static int do_create_class_files(struct scsi_tape *STp, int dev_num, int mode)
 {
 	int i, rew, error;
@@ -4402,6 +4442,9 @@ static int do_create_class_files(struct scsi_tape *STp, int dev_num, int mode)
 		error = class_device_create_file(st_class_member,
 				        &class_device_attr_default_compression);
 		if (error) goto out;
+		error = class_device_create_file(st_class_member,
+				        &class_device_attr_options);
+		if (error) goto out;
 
 		if (mode == 0 && rew == 0) {
 			error = sysfs_create_link(&STp->device->sdev_gendev.kobj,