scsi: sd: Add zoned capabilities device attribute

Export through sysfs as a scsi_disk attribute the zoned capabilities of a
disk ("zoned_cap" attribute file). This new attribute indicates in human
readable form (i.e. a string) the zoned block capabilities implemented by
the disk as found in the ZONED field of the disk block device
characteristics VPD page. The possible values are:

 - "none": ZONED=00b (not reported), regular disk

 - "host-aware": ZONED=01b, host-aware ZBC disk

 - "drive-managed": ZONED=10b, drive-managed ZBC disk (regular disk
   interface)

For completeness, also add the following value which is detected using the
device type rather than the ZONED field:

 - "host-managed": device type = 0x14 (TYPE_ZBC), host-managed ZBC disk

This new sysfs attribute is purely informational and complementary to the
"zoned" device request queue sysfs attribute as it allows applications and
user daemons (e.g.  udev) to easily differentiate regular disks from
drive-managed SMR disks without the need for direct access tools such as
provided by sg3utils.

Link: https://lore.kernel.org/r/20200515054856.1408575-1-damien.lemoal@wdc.comReviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sd.c

@@ -528,6 +528,21 @@ max_write_same_blocks_store(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RW(max_write_same_blocks);
 
+static ssize_t
+zoned_cap_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct scsi_disk *sdkp = to_scsi_disk(dev);
+
+	if (sdkp->device->type == TYPE_ZBC)
+		return sprintf(buf, "host-managed\n");
+	if (sdkp->zoned == 1)
+		return sprintf(buf, "host-aware\n");
+	if (sdkp->zoned == 2)
+		return sprintf(buf, "drive-managed\n");
+	return sprintf(buf, "none\n");
+}
+static DEVICE_ATTR_RO(zoned_cap);
+
 static struct attribute *sd_disk_attrs[] = {
 	&dev_attr_cache_type.attr,
 	&dev_attr_FUA.attr,
@@ -541,6 +556,7 @@ static struct attribute *sd_disk_attrs[] = {
 	&dev_attr_zeroing_mode.attr,
 	&dev_attr_max_write_same_blocks.attr,
 	&dev_attr_max_medium_access_timeouts.attr,
+	&dev_attr_zoned_cap.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(sd_disk);