[PATCH 2/6] null_blk: allow write zeores on membacked

[Chaitanya Kulkarni]

Add a helper functions to enable the REQ_OP_WRITE_ZEROES operations
when null_blk is configured with the membacked mode.

Since write-zeroes is a non-trivial I/O operation we need this to
add a blktest so we can test the non-trivial I/O path from the
application to the block layer.

Signed-off-by: Chaitanya Kulkarni <kch@xxxxxxxxxx>
---
 drivers/block/null_blk/main.c | 46 ++++++++++++++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index fc3e883f7b84..2d592b4eb815 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -420,6 +420,7 @@ NULLB_DEVICE_ATTR(blocking, bool, NULL);
 NULLB_DEVICE_ATTR(use_per_node_hctx, bool, NULL);
 NULLB_DEVICE_ATTR(memory_backed, bool, NULL);
 NULLB_DEVICE_ATTR(discard, bool, NULL);
+NULLB_DEVICE_ATTR(write_zeroes, bool, NULL);
 NULLB_DEVICE_ATTR(mbps, uint, NULL);
 NULLB_DEVICE_ATTR(cache_size, ulong, NULL);
 NULLB_DEVICE_ATTR(zoned, bool, NULL);
@@ -544,6 +545,7 @@ static struct configfs_attribute *nullb_device_attrs[] = {
 	&nullb_device_attr_power,
 	&nullb_device_attr_memory_backed,
 	&nullb_device_attr_discard,
+	&nullb_device_attr_write_zeroes,
 	&nullb_device_attr_mbps,
 	&nullb_device_attr_cache_size,
 	&nullb_device_attr_badblocks,
@@ -618,7 +620,7 @@ static ssize_t memb_group_features_show(struct config_item *item, char *page)
 			"poll_queues,power,queue_mode,shared_tag_bitmap,size,"
 			"submit_queues,use_per_node_hctx,virt_boundary,zoned,"
 			"zone_capacity,zone_max_active,zone_max_open,"
-			"zone_nr_conv,zone_size\n");
+			"zone_nr_conv,zone_size,write_zeroes\n");
 }
 
 CONFIGFS_ATTR_RO(memb_group_, features);
@@ -875,6 +877,24 @@ static void null_free_sector(struct nullb *nullb, sector_t sector,
 	}
 }
 
+static void null_zero_sector(struct nullb_device *d, sector_t sect,
+			     sector_t nr_sects, bool cache)
+{
+	struct radix_tree_root *root = cache ? &d->cache : &d->data;
+	struct nullb_page *t_page;
+	unsigned int offset;
+	void *dest;
+
+	t_page = radix_tree_lookup(root, sect >> PAGE_SECTORS_SHIFT);
+	if (!t_page)
+		return;
+
+	offset = (sect & SECTOR_MASK) << SECTOR_SHIFT;
+	dest = kmap_atomic(t_page->page);
+	memset(dest + offset, 0, SECTOR_SIZE * nr_sects);
+	kunmap_atomic(dest);
+}
+
 static struct nullb_page *null_radix_tree_insert(struct nullb *nullb, u64 idx,
 	struct nullb_page *t_page, bool is_cache)
 {
@@ -1191,6 +1211,27 @@ blk_status_t null_handle_discard(struct nullb_device *dev,
 	return BLK_STS_OK;
 }
 
+static blk_status_t null_handle_write_zeroes(struct nullb_device *dev,
+					     sector_t sector, sector_t nr_sectors)
+{
+	unsigned int bytes_left = nr_sectors << 9;
+	struct nullb *nullb = dev->nullb;
+	size_t curr_bytes;
+
+	spin_lock_irq(&nullb->lock);
+	while (bytes_left > 0) {
+		curr_bytes = min_t(size_t, bytes_left, nullb->dev->blocksize);
+		nr_sectors = curr_bytes >> SECTOR_SHIFT;
+		null_zero_sector(nullb->dev, sector, nr_sectors, false);
+		if (null_cache_active(nullb))
+			null_zero_sector(nullb->dev, sector, nr_sectors, true);
+		sector += nr_sectors;
+		bytes_left -= curr_bytes;
+	}
+	spin_unlock_irq(&nullb->lock);
+	return BLK_STS_OK;
+}
+
 static int null_handle_flush(struct nullb *nullb)
 {
 	int err;
@@ -1357,6 +1398,9 @@ static inline blk_status_t null_handle_memory_backed(struct nullb_cmd *cmd,
 	if (op == REQ_OP_DISCARD)
 		return null_handle_discard(dev, sector, nr_sectors);
 
+	if (op == REQ_OP_WRITE_ZEROES)
+		return null_handle_write_zeroes(dev, sector, nr_sectors);
+
 	if (dev->queue_mode == NULL_Q_BIO)
 		err = null_handle_bio(cmd);
 	else
-- 
2.29.0