block: export 'ro' sysfs attribute for partitions

We already export 'ro' for the disk. This adds the same attribute
for partitions.

Cc: Karel Zak <kzak@redhat.com>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

fs/partitions/check.c

@@ -237,6 +237,13 @@ ssize_t part_size_show(struct device *dev,
 	return sprintf(buf, "%llu\n",(unsigned long long)p->nr_sects);
 }
 
+ssize_t part_ro_show(struct device *dev,
+		       struct device_attribute *attr, char *buf)
+{
+	struct hd_struct *p = dev_to_part(dev);
+	return sprintf(buf, "%d\n", p->policy ? 1 : 0);
+}
+
 ssize_t part_alignment_offset_show(struct device *dev,
 				   struct device_attribute *attr, char *buf)
 {
@@ -312,6 +319,7 @@ ssize_t part_fail_store(struct device *dev,
 static DEVICE_ATTR(partition, S_IRUGO, part_partition_show, NULL);
 static DEVICE_ATTR(start, S_IRUGO, part_start_show, NULL);
 static DEVICE_ATTR(size, S_IRUGO, part_size_show, NULL);
+static DEVICE_ATTR(ro, S_IRUGO, part_ro_show, NULL);
 static DEVICE_ATTR(alignment_offset, S_IRUGO, part_alignment_offset_show, NULL);
 static DEVICE_ATTR(discard_alignment, S_IRUGO, part_discard_alignment_show,
 		   NULL);
@@ -326,6 +334,7 @@ static struct attribute *part_attrs[] = {
 	&dev_attr_partition.attr,
 	&dev_attr_start.attr,
 	&dev_attr_size.attr,
+	&dev_attr_ro.attr,
 	&dev_attr_alignment_offset.attr,
 	&dev_attr_discard_alignment.attr,
 	&dev_attr_stat.attr,