nullb: badbblocks support

Sometime disk could have tracks broken and data there is inaccessable,
but data in other parts can be accessed in normal way. MD RAID supports
such disks. But we don't have a good way to test it, because we can't
control which part of a physical disk is bad. For a virtual disk, this
can be easily controlled.

This patch adds a new 'badblock' attribute. Configure it in this way:
echo "+1-100" > xxx/badblock, this will make sector [1-100] as bad
blocks.
echo "-20-30" > xxx/badblock, this will make sector [20-30] good

If badblocks are accessed, the nullb disk will return IO error. Other
parts of the disk can accessed in normal way.
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/null_blk.c

@@ -14,6 +14,7 @@
 #include <linux/hrtimer.h>
 #include <linux/lightnvm.h>
 #include <linux/configfs.h>
+#include <linux/badblocks.h>
 
 #define SECTOR_SHIFT		9
 #define PAGE_SECTORS_SHIFT	(PAGE_SHIFT - SECTOR_SHIFT)
@@ -93,6 +94,7 @@ struct nullb_device {
 	struct radix_tree_root cache; /* disk cache data */
 	unsigned long flags; /* device flags */
 	unsigned int curr_cache;
+	struct badblocks badblocks;
 
 	unsigned long size; /* device size in MB */
 	unsigned long completion_nsec; /* time in ns to complete a request */
@@ -386,6 +388,59 @@ static ssize_t nullb_device_power_store(struct config_item *item,
 
 CONFIGFS_ATTR(nullb_device_, power);
 
+static ssize_t nullb_device_badblocks_show(struct config_item *item, char *page)
+{
+	struct nullb_device *t_dev = to_nullb_device(item);
+
+	return badblocks_show(&t_dev->badblocks, page, 0);
+}
+
+static ssize_t nullb_device_badblocks_store(struct config_item *item,
+				     const char *page, size_t count)
+{
+	struct nullb_device *t_dev = to_nullb_device(item);
+	char *orig, *buf, *tmp;
+	u64 start, end;
+	int ret;
+
+	orig = kstrndup(page, count, GFP_KERNEL);
+	if (!orig)
+		return -ENOMEM;
+
+	buf = strstrip(orig);
+
+	ret = -EINVAL;
+	if (buf[0] != '+' && buf[0] != '-')
+		goto out;
+	tmp = strchr(&buf[1], '-');
+	if (!tmp)
+		goto out;
+	*tmp = '\0';
+	ret = kstrtoull(buf + 1, 0, &start);
+	if (ret)
+		goto out;
+	ret = kstrtoull(tmp + 1, 0, &end);
+	if (ret)
+		goto out;
+	ret = -EINVAL;
+	if (start > end)
+		goto out;
+	/* enable badblocks */
+	cmpxchg(&t_dev->badblocks.shift, -1, 0);
+	if (buf[0] == '+')
+		ret = badblocks_set(&t_dev->badblocks, start,
+			end - start + 1, 1);
+	else
+		ret = badblocks_clear(&t_dev->badblocks, start,
+			end - start + 1);
+	if (ret == 0)
+		ret = count;
+out:
+	kfree(orig);
+	return ret;
+}
+CONFIGFS_ATTR(nullb_device_, badblocks);
+
 static struct configfs_attribute *nullb_device_attrs[] = {
 	&nullb_device_attr_size,
 	&nullb_device_attr_completion_nsec,
@@ -404,6 +459,7 @@ static struct configfs_attribute *nullb_device_attrs[] = {
 	&nullb_device_attr_discard,
 	&nullb_device_attr_mbps,
 	&nullb_device_attr_cache_size,
+	&nullb_device_attr_badblocks,
 	NULL,
 };
 
@@ -411,6 +467,7 @@ static void nullb_device_release(struct config_item *item)
 {
 	struct nullb_device *dev = to_nullb_device(item);
 
+	badblocks_exit(&dev->badblocks);
 	null_free_device_storage(dev, false);
 	null_free_dev(dev);
 }
@@ -456,7 +513,7 @@ nullb_group_drop_item(struct config_group *group, struct config_item *item)
 
 static ssize_t memb_group_features_show(struct config_item *item, char *page)
 {
-	return snprintf(page, PAGE_SIZE, "memory_backed,discard,bandwidth,cache\n");
+	return snprintf(page, PAGE_SIZE, "memory_backed,discard,bandwidth,cache,badblocks\n");
 }
 
 CONFIGFS_ATTR_RO(memb_group_, features);
@@ -500,6 +557,11 @@ static struct nullb_device *null_alloc_dev(void)
 		return NULL;
 	INIT_RADIX_TREE(&dev->data, GFP_ATOMIC);
 	INIT_RADIX_TREE(&dev->cache, GFP_ATOMIC);
+	if (badblocks_init(&dev->badblocks, 0)) {
+		kfree(dev);
+		return NULL;
+	}
+
 	dev->size = g_gb * 1024;
 	dev->completion_nsec = g_completion_nsec;
 	dev->submit_queues = g_submit_queues;
@@ -1166,6 +1228,30 @@ static blk_status_t null_handle_cmd(struct nullb_cmd *cmd)
 		}
 	}
 
+	if (nullb->dev->badblocks.shift != -1) {
+		int bad_sectors;
+		sector_t sector, size, first_bad;
+		bool is_flush = true;
+
+		if (dev->queue_mode == NULL_Q_BIO &&
+				bio_op(cmd->bio) != REQ_OP_FLUSH) {
+			is_flush = false;
+			sector = cmd->bio->bi_iter.bi_sector;
+			size = bio_sectors(cmd->bio);
+		}
+		if (dev->queue_mode != NULL_Q_BIO &&
+				req_op(cmd->rq) != REQ_OP_FLUSH) {
+			is_flush = false;
+			sector = blk_rq_pos(cmd->rq);
+			size = blk_rq_sectors(cmd->rq);
+		}
+		if (!is_flush && badblocks_check(&nullb->dev->badblocks, sector,
+				size, &first_bad, &bad_sectors)) {
+			cmd->error = BLK_STS_IOERR;
+			goto out;
+		}
+	}
+
 	if (dev->memory_backed) {
 		if (dev->queue_mode == NULL_Q_BIO) {
 			if (bio_op(cmd->bio) == REQ_OP_FLUSH)
@@ -1180,6 +1266,7 @@ static blk_status_t null_handle_cmd(struct nullb_cmd *cmd)
 		}
 	}
 	cmd->error = errno_to_blk_status(err);
+out:
 	/* Complete IO by inline, softirq or timer */
 	switch (dev->irqmode) {
 	case NULL_IRQ_SOFTIRQ: