null_blk: return fixed zoned reads > write pointer

A zoned block device maintains a write pointer within a zone, and reads
beyond the write pointer are undefined. Fill data buffer returned above
the write pointer with 0xFF.
Signed-off-by: Ajay Joshi <ajay.joshi@wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Matias Bjørling <matias.bjorling@wdc.com>
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/null_blk.h

@@ -96,6 +96,8 @@ int null_zone_report(struct gendisk *disk, sector_t sector,
 blk_status_t null_handle_zoned(struct nullb_cmd *cmd,
 				enum req_opf op, sector_t sector,
 				sector_t nr_sectors);
+size_t null_zone_valid_read_len(struct nullb *nullb,
+				sector_t sector, unsigned int len);
 #else
 static inline int null_zone_init(struct nullb_device *dev)
 {
@@ -115,5 +117,11 @@ static inline blk_status_t null_handle_zoned(struct nullb_cmd *cmd,
 {
 	return BLK_STS_NOTSUPP;
 }
+static inline size_t null_zone_valid_read_len(struct nullb *nullb,
+					      sector_t sector,
+					      unsigned int len)
+{
+	return len;
+}
 #endif /* CONFIG_BLK_DEV_ZONED */
 #endif /* __NULL_BLK_H */

drivers/block/null_blk_main.c

@@ -1022,6 +1022,16 @@ static int copy_from_nullb(struct nullb *nullb, struct page *dest,
 	return 0;
 }
 
+static void nullb_fill_pattern(struct nullb *nullb, struct page *page,
+			       unsigned int len, unsigned int off)
+{
+	void *dst;
+
+	dst = kmap_atomic(page);
+	memset(dst + off, 0xFF, len);
+	kunmap_atomic(dst);
+}
+
 static void null_handle_discard(struct nullb *nullb, sector_t sector, size_t n)
 {
 	size_t temp;
@@ -1062,10 +1072,24 @@ static int null_transfer(struct nullb *nullb, struct page *page,
 	unsigned int len, unsigned int off, bool is_write, sector_t sector,
 	bool is_fua)
 {
+	struct nullb_device *dev = nullb->dev;
+	unsigned int valid_len = len;
 	int err = 0;
 
 	if (!is_write) {
-		err = copy_from_nullb(nullb, page, off, sector, len);
+		if (dev->zoned)
+			valid_len = null_zone_valid_read_len(nullb,
+				sector, len);
+
+		if (valid_len) {
+			err = copy_from_nullb(nullb, page, off,
+				sector, valid_len);
+			off += valid_len;
+			len -= valid_len;
+		}
+
+		if (len)
+			nullb_fill_pattern(nullb, page, len, off);
 		flush_dcache_page(page);
 	} else {
 		flush_dcache_page(page);

drivers/block/null_blk_zoned.c

@@ -84,6 +84,24 @@ int null_zone_report(struct gendisk *disk, sector_t sector,
 	return 0;
 }
 
+size_t null_zone_valid_read_len(struct nullb *nullb,
+				sector_t sector, unsigned int len)
+{
+	struct nullb_device *dev = nullb->dev;
+	struct blk_zone *zone = &dev->zones[null_zone_no(dev, sector)];
+	unsigned int nr_sectors = len >> SECTOR_SHIFT;
+
+	/* Read must be below the write pointer position */
+	if (zone->type == BLK_ZONE_TYPE_CONVENTIONAL ||
+	    sector + nr_sectors <= zone->wp)
+		return len;
+
+	if (sector > zone->wp)
+		return 0;
+
+	return (zone->wp - sector) << SECTOR_SHIFT;
+}
+
 static blk_status_t null_zone_write(struct nullb_cmd *cmd, sector_t sector,
 		     unsigned int nr_sectors)
 {
@@ -121,8 +139,7 @@ static blk_status_t null_zone_write(struct nullb_cmd *cmd, sector_t sector,
 static blk_status_t null_zone_reset(struct nullb_cmd *cmd, sector_t sector)
 {
 	struct nullb_device *dev = cmd->nq->dev;
-	unsigned int zno = null_zone_no(dev, sector);
-	struct blk_zone *zone = &dev->zones[zno];
+	struct blk_zone *zone = &dev->zones[null_zone_no(dev, sector)];
 	size_t i;
 
 	switch (req_op(cmd->rq)) {