[PATCH] null_blk: return fixed data for reads greater than zone write pointer

[Ajay Joshi]

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@xxxxxxx>
Reviewed-by: Damien Le Moal <damien.lemoal@xxxxxxx>
Reviewed-by: Matias BjÃrling <matias.bjorling@xxxxxxx>
---
 drivers/block/null_blk.h       |  7 +++++++
 drivers/block/null_blk_main.c  | 26 +++++++++++++++++++++++++-
 drivers/block/null_blk_zoned.c | 18 ++++++++++++++++++
 3 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/drivers/block/null_blk.h b/drivers/block/null_blk.h
index 34b22d6523ba..fa82c4d96c8a 100644
--- a/drivers/block/null_blk.h
+++ b/drivers/block/null_blk.h
@@ -94,6 +94,8 @@ int null_zone_report(struct gendisk *disk, sector_t sector,
 void null_zone_write(struct nullb_cmd *cmd, sector_t sector,
 			unsigned int nr_sectors);
 void null_zone_reset(struct nullb_cmd *cmd, sector_t sector);
+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)
 {
@@ -112,5 +114,10 @@ static inline void null_zone_write(struct nullb_cmd *cmd, sector_t sector,
 {
 }
 static inline void null_zone_reset(struct nullb_cmd *cmd, sector_t sector) {}
+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 */
diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c
index 99328ded60d1..ce66f4e6268a 100644
--- a/drivers/block/null_blk_main.c
+++ b/drivers/block/null_blk_main.c
@@ -996,6 +996,16 @@ 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;
@@ -1037,9 +1047,23 @@ static int null_transfer(struct nullb *nullb, struct page *page,
 	bool is_fua)
 {
 	int err = 0;
+	struct nullb_device *dev = nullb->dev;
+	unsigned int valid_len = len;
 
 	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);
diff --git a/drivers/block/null_blk_zoned.c b/drivers/block/null_blk_zoned.c
index fca0c97ff1aa..20a3c08e628c 100644
--- a/drivers/block/null_blk_zoned.c
+++ b/drivers/block/null_blk_zoned.c
@@ -85,6 +85,24 @@ 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;
+}
+
 void null_zone_write(struct nullb_cmd *cmd, sector_t sector,
 		     unsigned int nr_sectors)
 {
-- 
2.19.1