From: Tom Coughlan <coughlan@redhat.com>
Date: Tue, 1 Dec 2009 16:17:53 -0500
Subject: [scsi] st: display current settings of option bits
Message-id: <1259684273.3963.26.camel@localhost.localdomain>
Patchwork-id: 21570
O-Subject: Re: [RHEL5.5 PATCH] st: display current settings of the st driver
	option bits
Bugzilla: 501030
RH-Acked-by: Prarit Bhargava <prarit@redhat.com>
RH-Acked-by: Tomas Henzl <thenzl@redhat.com>

To fix BZ https://bugzilla.redhat.com/show_bug.cgi?id=501030

The SCSI tape driver (st) has numerous option bits that can be set by
ioclt or by the mt-st utility.

buffer-writes  buffered writes enabled
async-writes   asynchronous writes enabled
read-ahead     read-ahead for fixed block size
debug          debugging (if compiled into driver)
two-fms        write two filemarks when file closed
fast-eod       space directly to eod (and lose file number)
no-wait        dont wait until rewind, etc. complete
auto-lock      automatically lock/unlock drive door
def-writes     the block size and density are for writes
can-bsr        drive can space backwards as well
no-blklimits   drive doesnt support read block limits
can-partitions drive can handle partitioned tapes
scsi2logical   seek and tell use SCSI-2 logical block addresses instead
of
               device dependent addresses
sysv           enable the System V semantics

and the new bit we added in 5.4:

sili           suppress incorrect length indicator (see BZ 457970).

There is no easy way to determine the current settings of these option
bits.

The following upstream commit makes this information available in
sysfs:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=b174be02f3634460ac215d249617dee5ae446ae1

This capability should be added to RHEL 5, to make system management and
support easier.

Brew build:
https://brewweb.devel.redhat.com/taskinfo?taskID=2109990

I tested this on a DLT8000 drive. I wrote the option bits with mt:

mt -f /dev/st0 stoptions 0x4fa3

and read them with sysfs:

cat /sys/class/scsi_tape/st0/options
0x00004fa3

A newer version of the mt-st management utility also formats and
displays this information nicely. This is under consideration for a
future RHEL 5 update as well (BZ 501014).

Signed-off-by: Don Zickus <dzickus@redhat.com>

diff --git a/Documentation/scsi/st.txt b/Documentation/scsi/st.txt
index 00815c0..eb02cf0 100644
--- a/Documentation/scsi/st.txt
+++ b/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). 
 
diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index f50405f..2db8709 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -4325,6 +4325,46 @@ 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 void do_create_class_files(struct scsi_tape *STp, int dev_num, int mode)
 {
 	int i, rew, error;
@@ -4360,6 +4400,8 @@ static void do_create_class_files(struct scsi_tape *STp, int dev_num, int mode)
 					 &class_device_attr_default_density);
 		class_device_create_file(st_class_member,
 					 &class_device_attr_default_compression);
+		class_device_create_file(st_class_member,
+				        &class_device_attr_options);
 		if (mode == 0 && rew == 0) {
 			error = sysfs_create_link(&STp->device->sdev_gendev.kobj,
 						  &st_class_member->kobj,