md/raid5: support config stripe_size by sysfs entry

Adding a new 'stripe_size' sysfs entry to set and show stripe_size.
stripe_size should not be bigger than PAGE_SIZE, and it requires to
be multiple of 4096. We can adjust stripe_size by writing value into
sysfs entry, likely, set stripe_size as 16KB:

          echo 16384 > /sys/block/md1/md/stripe_size

Show current stripe_size value:

          cat /sys/block/md1/md/stripe_size

For PAGE_SIZE is equal to 4096, 'stripe_size' can just be read.
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Song Liu <songliubraving@fb.com>

drivers/md/raid5.c

@@ -6503,6 +6503,77 @@ raid5_rmw_level = __ATTR(rmw_level, S_IRUGO | S_IWUSR,
 			 raid5_show_rmw_level,
 			 raid5_store_rmw_level);
 
+static ssize_t
+raid5_show_stripe_size(struct mddev  *mddev, char *page)
+{
+	struct r5conf *conf;
+	int ret = 0;
+
+	spin_lock(&mddev->lock);
+	conf = mddev->private;
+	if (conf)
+		ret = sprintf(page, "%lu\n", RAID5_STRIPE_SIZE(conf));
+	spin_unlock(&mddev->lock);
+	return ret;
+}
+
+#if PAGE_SIZE != DEFAULT_STRIPE_SIZE
+static ssize_t
+raid5_store_stripe_size(struct mddev  *mddev, const char *page, size_t len)
+{
+	struct r5conf *conf;
+	unsigned long new;
+	int err;
+
+	if (len >= PAGE_SIZE)
+		return -EINVAL;
+	if (kstrtoul(page, 10, &new))
+		return -EINVAL;
+
+	/*
+	 * The value should not be bigger than PAGE_SIZE. It requires to
+	 * be multiple of DEFAULT_STRIPE_SIZE.
+	 */
+	if (new % DEFAULT_STRIPE_SIZE != 0 || new > PAGE_SIZE || new == 0)
+		return -EINVAL;
+
+	err = mddev_lock(mddev);
+	if (err)
+		return err;
+
+	conf = mddev->private;
+	if (!conf) {
+		err = -ENODEV;
+		goto out_unlock;
+	}
+
+	if (new == conf->stripe_size)
+		goto out_unlock;
+
+	pr_debug("md/raid: change stripe_size from %lu to %lu\n",
+			conf->stripe_size, new);
+
+	mddev_suspend(mddev);
+	conf->stripe_size = new;
+	conf->stripe_shift = ilog2(new) - 9;
+	conf->stripe_sectors = new >> 9;
+	mddev_resume(mddev);
+
+out_unlock:
+	mddev_unlock(mddev);
+	return err ?: len;
+}
+
+static struct md_sysfs_entry
+raid5_stripe_size = __ATTR(stripe_size, 0644,
+			 raid5_show_stripe_size,
+			 raid5_store_stripe_size);
+#else
+static struct md_sysfs_entry
+raid5_stripe_size = __ATTR(stripe_size, 0444,
+			 raid5_show_stripe_size,
+			 NULL);
+#endif
 
 static ssize_t
 raid5_show_preread_threshold(struct mddev *mddev, char *page)
@@ -6691,6 +6762,7 @@ static struct attribute *raid5_attrs[] =  {
 	&raid5_group_thread_cnt.attr,
 	&raid5_skip_copy.attr,
 	&raid5_rmw_level.attr,
+	&raid5_stripe_size.attr,
 	&r5c_journal_mode.attr,
 	&ppl_write_hint.attr,
 	NULL,